DEV Community: ROHIT KUMAR

For Loop & For-Each Loop

ROHIT KUMAR — Fri, 15 Oct 2021 21:41:50 +0000

What is LOOP

Loops in JAVA are used to automate some particular task which is repeated for no.s of times.
Suppose that, you’re creating a program that print the fist five natural number its very easy to just write print statement five time,

BUT

What if you want to print the first 1000 natural number .
Its not feasible to just write 1000 lines of code which just do similar task here you will use a loop to automate the task
That will also reduces the line of code and increase readbility.

Java provides different types of loops,
Here we will see about For loop and For-each loop, with reference to a few examples and Java programs.

`1️⃣.FOR LOOP`

It is used to iterate a part of the program several times if the number of iteration is fixed.

SYNTAX:-

for (initialization;condition;updation)
{
     // body of the loop;
}

Initialization is used to initialize a variable that keeps track of how many times the loop has executed.
Condition is a boolean expression whose condition is either true or false
1. If its true then executes the body of the loop.
2. If its false then its exit the loop.
Body of the loop Its the main code which needs to be repeated written inside the curly bracket which is called block of loop.
Updation is executed after the body of the loop and updates the initialization variable.

FLOWCHART:-

EXAMPLE 1:-

You need to print the first 10000 natural nos

class For{
  public static void main (String[]args){
    for(Int i =1;i<=10000;i++){
      System.out.print(i);
    }
  }
}

OUTPUT:

1
2
3
4
5
...so on

EXAMPLE 2:-

You are given the Array of students mark you need to find the maximum mark obtained using for loop

class Foreg 
{
    public static void main(String[] args)
    {
            int[] marks = { 400, 790, 600, 895 ,790 ,450, 670, 200,890  };

            int max=-1;
            // for each loop
            for (int i=0;i<marks.length();i++)
            {
            if (marks[i] > max)
             {
                max = marks[i];
             }
            }
            System.out.println("The Maximum mark is: " + max) ;
    }
}

OUTPUT:

The Maximum marks is: 895

`2️⃣.FOR EACH LOOP`

Java for-each loop or enhanced for loop introduced in Java 5.
Its more simpler way to iterate through the elements of a collection or array.
Its used when we dont need know the index of the current array and its iterate through the elements in sequentail order

Note:

SYNTAX:-

for (dataType item : collection obj/array) {
    // Body of the loop
}

DataType is the type of data our item uses.
Item is a variable which stores each value of the Collection as we iterate through the loop.
Collection is an array or collection variable through which the for loop will iterate.

HOW ITS WORK:-

WE declare the variable(item) which is of same type as the base type of array/collection, followed by a colon, which is then followed by the array/collection name.
Now we use the our item variable instead of indexed variable of array to loop traverses the array until the last element one by one in increasing order.
It stores each item in the item variable, then executes the code stored within the loop body.

FLOWCHART:-

ADVANTAGE:-

It makes the code more readable.
It reduces the possibilty of bug.

DRAWBACK:-

You cant modify the array element because the object/variable is immutable when enhanced for loop is used.
It can only move single steps forward.
Do not keep track of index. So we can not obtain array index using For-Each loop
It cant traverse in the reverse order

EXAMPLE 1:-

You are given the Array of students mark you need to find the maximum mark obtained by using Enhanced For Loop

class ForEacheg 
{
    public static void main(String[] arg)
    {
            int[] marks = { 400, 790, 600, 895 ,790 ,450, 670, 200,890  };

            int max=-1;
            // for each loop
            for (int num : marks)
            {
            if (num > max)
             {
                max = num;
             }
            }
            System.out.println("The Maximum mark is: " + max);
    }
}

OUTPUT:

The Maximum marks is: 895

EXAMPLE 2:-

You are need to print the all the menu item of coffee shop stored in the ArrayList


public class ForEach_Collection {

    public static void main(String[] args) {

        ArrayList<String> menu = new ArrayList<String>();

        menu.add("Cafe latte");
        menu.add("Cold Coffee");
        menu.add("Cappuccino");
        menu.add("Espresso")
        menu.add("Macchiato")

        // for-each loop
        for (String item : menu) {
        System.out.println(item);
        }
    }
}

OUTPUT

Cafe latte
Cold Coffee
Cappuccino
Espresso
Macchiato

REFERENCE 1,2

IMAGE SOURCE 1,2

Thank You! 😊

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Common Android Views Cheat Sheet

ROHIT KUMAR — Sun, 15 Aug 2021 04:02:07 +0000

Here I am providing the list of some common android View cheatsheet used for building UI that we see on our devices

It helps you with -
- Know Code Syntax for each View
- I have provided a Link referring to Android documentation for each view
- A note on each View describing briefly about it

1. TextView

Shows text

<TextView
 android:id="@+id/title_text_view"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content" 
 android:text="@string/my_photos"
 android:textAppearance="?android:textAppearanceLarge"
 android:textColor="#4689C8"
 android:textStyle="bold" />

2. ImageView

Shows Image

<ImageView
 android:id="@+id/photo_image_view"
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 android:scaleType="centerCrop"
 android:src="@drawable/beach" />

3. Button

Use for user interaction do some specific task on Click

<Button
 android:id="@+id/next_button"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:text="@string/next" />

4. View

Plain rectangle (can be used as a divider)

<View
 android:layout_width="match_parent"
 android:layout_height="100dp"
 android:background="#4E4B4F" />

5. EditText

Text field that you can use to take user input

<EditText
 android:id="@+id/album_description_view"
 android:layout_width="match_parent"
 android:layout_height="wrap_content"
 android:hint="@string/album_description"
 android:inputType="textMultiLine" />

6. Spinner

Click on it to show a list of dropdown options

<Spinner
 android:id="@+id/sort_by_spinner"
 android:layout_width="match_parent"
 android:layout_height="wrap_content" />

7. CheckBox

Checkbox with text label used to check or uncheck some option

<CheckBox
 android:id="@+id/notify_me_checkbox"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content" 
 android:text="@string/notify_me"
 android:textAppearance="?android:textAppearanceMedium" />

8. RadioButton

Radio button (where you can select one out of a group of
radio buttons)

<RadioGroup
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:orientation="vertical">
 <RadioButton
 android:id="@+id/yes_radio_button"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:text="@string/yes"
 android:textAppearance="?android:textAppearanceMedium" />
 <RadioButton
 android:id="@+id/no_radio_button"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:text="@string/no"
 android:textAppearance="?android:textAppearanceMedium" />
</RadioGroup>

9. RatingBar

Star rating

<RatingBar
 android:id="@+id/rating_bar"
 style="?android:attr/ratingBarStyleSmall"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content" 
 android:numStars="5"
 android:rating="2.5"
 android:stepSize="0.5" />

10. Switch

On / off switch that you can drag right or left (or just tap to toggle the state)

<Switch
 android:id="@+id/backup_photos_switch"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content" 
 android:text="@string/auto_backup_photos"
 android:textAppearance="?android:textAppearanceSmall" />

11. SeekBar

Displays progress and allows you
to drag the handle anywhere in
the bar (i.e. for music or video
player)

<SeekBar
 android:id="@+id/seek_bar"
 android:layout_width="match_parent"
 android:layout_height="wrap_content" 
 android:max="100"
 android:progress="20" />

12. SearchView

A search field that you can type
a query into

<SearchView
 android:id="@+id/search_viewr"
 android:layout_width="match_parent"
 android:layout_height="wrap_content" 
 android:iconifiedByDefault="false"
 android:queryHint="@string/search_photos" />

13. ProgressBar

Loading spinner

<ProgressBar
 android:id="@+id/loading_spinner"
 style="@style/Widget.AppCompat.ProgressBar"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content" />

14. ProgressBar

Horizontal loading indicator

<ProgressBar
android:id="@+id/progress_bar"
 style="@style/Widget.AppCompat.ProgressBar.Horizontal"
 android:layout_width="match_parent"
 android:layout_height="wrap_content" 
 android:indeterminate="false"
 android:max="100"
 android:progress="40"/>
ProgressBar

That's all for today!

References:

https://s3.amazonaws.com/video.udacity-data.com/topher/2017/July/595ab9de_common-android-views-cheat-sheet/common-android-views-cheat-sheet.pdf

I referred from here because I found this valuable and reliable, as it's from Google and uses it in there courses provided by them
This article will help you directly use the gist, from here

If you liked it, plz do share
Also if you got any questions or suggestions feel free to comment down below.

If you are thinking of starting an Android Development you can check this blog,

What to Learn to get started with Android App Development?

ROHIT KUMAR ・ Jul 12 '21

#beginners #android #kotlin #java

Thank You! 😊

You can follow me on
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Android Basics: Using Relative layout

ROHIT KUMAR — Sat, 07 Aug 2021 13:29:04 +0000

In this article,

We will make a non-interactive app with just using Relative Layout ViewGroup and no line of extra java code
and also learn along the way about Relative Layout .

The entire content is inspired by,
Google's udacity course Android Basics: User Interface. It's the first part of the five parts Android Basics Nanodegree Program series, This course is for basics of Android and Java programming .
So I would be writing a blog series and this is my second blog in this series.

UI design of our app would look like this,

What is Relative Layout❓

A View is a rectangular area on the screen.
A ViewGroup is a big View that can contain smaller Views inside of it. The smaller Views are called the children of the ViewGroup and ViewGroup is called the parent of its children.
Basically, it is used to display more views neatly on the screen.

A RelativeLayout is a common type of ViewGroup that lets us position child views relative to sibling elements (such as to the left-of or below another view) or relative to the parent RelativeLayout area (such as aligned to the bottom, left or center).

Positioning Views

By default, all child views are drawn at the top-left of the layout , so you must define the position of each view using the various layout properties available from RelativeLayout.LayoutParams.

RelativeLayout.LayoutParams

The View within the relative layout, uses the value of these Relative layout parameters to determine where to position the view on the screen.
The value for each layout property is either a boolean to enable a layout position relative to the parent RelativeLayout or an ID that references another view in the layout against which the view should be positioned.

The following are the major attributes in RelativeLayout available to its view.
They lay across four different categories:

1️⃣Align by the parent view

These types of attributes make the view be fixed to any side of the parent view.
Its attributes have two values either true or false boolean value.

XML Attributes	Description
android:layout_alignParentBottom	If true, make the bottom edge of this view match the bottom edge of the parent.
android:layout_alignParentEnd	If true, makes the end edge of this view match the end edge of the parent.
android:layout_alignParentLeft	If true, make the left edge of this view match the left edge of the parent.
android:layout_alignParentRight	If true, make the right edge of this view match the right edge of the parent.
android:layout_alignParentStart	If true, make the start edge of this view match the start edge of the parent.
android:layout_alignParentTop	If true, make the top edge of this view match the top edge of the parent

Examples.

2️⃣Center relative to Parent View

Its attributes have two values either true or false boolean value.
When you want to place your Views in the center relative to the parent, you can use the following 3 attributes:

XML Attributes	Description
android:layout_centerHorizontal	If true, centers this child horizontally within its parent.
android:layout_centerInParent	If true, centers this child horizontally and vertically within its parent.
android:layout_centerVertical	If true, centers this child vertically within its parent.

Examples.

3️⃣Relative to Child View

We can position the new views relative to other existing views.
We just need to create the id of the Anchor view(the main child view its position should be fixed ) using the attributes android:id .
Now, these attributes value is the same ID that refers to the anchor view against which the view should be positioned.
For eg.
android:layout_toLeftOf="@id/name_of_anchorView"

Following attributes can be used for doing so.

XML Attributes	Description
android:layout_above	Positions the bottom edge of this view above the given anchor view ID.
android:layout_below	Positions the top edge of this view below the given anchor view ID.
android:layout_toEndOf	Positions the start edge of this view to the end of the given anchor view ID.
android:layout_toLeftOf	Positions the right edge of this view to the left of the given anchor view ID.
android:layout_toRightOf	Positions the left edge of this view to the right of the given anchor view ID.
android:layout_toStartOf	Positions the end edge of this view to the start of the given anchor view ID.

Examples.

4️⃣Align View relative to Child View

If you want to align the new view relative to any existing view, then you can use the following attributes.
Here also these attributes value will be id which refers to anchor View

XML Attributes	Description
android:layout_alignBaseline	Positions the baseline of this view on the baseline of the given anchor view ID.
android:layout_alignBottom	Makes the bottom edge of this view match the bottom edge of the given anchor view ID.
android:layout_alignEnd	Makes the end edge of this view match the end edge of the given anchor view ID.
android:layout_alignLeft	Makes the left edge of this view match the left edge of the given anchor view ID.
android:layout_alignRight	Makes the right edge of this view match the right edge of the given anchor view ID.
android:layout_alignStart	Makes the start edge of this view match the start edge of the given anchor view ID.
android:layout_alignTop	Makes the top edge of this view match the top edge of the given anchor view ID.

Examples.

Now,

We will make a Birthday Card app which will basically be non-interactive i.e. no line of extra java code just an XML code to design the UI of our app, by using Relative Layout.

Whenever ,we write the code of XML Layout ,think of 3 step in mind

Step 1->Select the Views

Step 2->Position the Views

Step 3->Styles the Views

Step 1:Select the View

Before writing the code for the UI, we must design or think about how our layout would look so either make the design or diagram of the UI page, then think about how to make it to code.

Our layout would look like this,

Looking at the image it's clear that,

We will be using 2 TextView 1 ImageView ss, we see there is an image in the background on the image and their Text written at two different places.

Step 2:Position the Views

Now to choose, which ViewGroup we should use to position the views, as we see two TextView are overlapping over the ImageView hence, Relative Layout is perfect for this situation, help in positioning the two text view as they are positioned.

Overlapping View

In Relative Layout ,the Views overlap and stack up from top to down manner correspondingly as written in XML

Insert an image

Save the image in drawable folder and use an attributes android:src to show image
Here we should also centre crop to image so that it will scale up the image and encrop it , to make a full bleed image, and give a nice immersive feel, and its width and height to match_parent so that ,image take whole space of the screen size

    <ImageView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:scaleType="centerCrop"
        android:src="@drawable/happybirthday" />

Positioning the TextView

Now as we choosed Relative Layout , so think about how to align and position views with respect to other.

<TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="HAPPY BIRTHDAY" />
<TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentEnd="true"
        android:layout_alignParentBottom="true"
        android:text="  ROHIT.K 🎊 " />

HAPPY BIRTHDAY TextView will by default be placed at top right corner we don't need to add any layout parameter to position view
ROHIT.K TextView needed to be positioned at the bottom-right corner we will use two attributes as shown above and make that value be true
height and width should be set to wrap_content as we need to be flexible with the amount of text written

Now the with this code, the layout would look like this...

Step 3: Style the Views

We need to add or change some more attributes, to add some style and make our UI look better.
So add style, to make the UI more beautiful and for better user experience

For styling, we can change the size, front & color of the text, according to the situation.
We can also change the color of the background color of the TextView.
And best is to also add padding or margin so that makes it more readable & not smushed at the corner.

For making Text Larger

Make the size of text 36sp using attributes,
android:textSize

Setting the Font

Set the Text font to sans-serif-light using attributes,
android:fontFamily

Setting the color

use the attributes android:textColor

Background of textView

for changing background color we will attributes android:background

Add padding and margin

we will use the attributes android:padding and android:layout_marginwe can use either of the both or both as per situation.

Styling depends upon how better we can think, to make our app look better and give an aesthetic look
It totally depends upon the experience and our creativity

THIS Image of our app, how it will look like after writing these codes in XML

Code to write in activity_main.xml inside Android Studio
located inside res folder

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <ImageView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:contentDescription="@null"
        android:scaleType="centerCrop"
        android:src="@drawable/happybirthday" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="20dp"
        android:background="#9E03DAC5"
        android:fontFamily="sans-serif-light"
        android:padding="30dp"
        android:text="HAPPY BIRTHDAY"
        android:textColor="@android:color/white"
        android:textSize="36sp" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentEnd="true"
        android:layout_alignParentBottom="true"
        android:background="#C8FFFFFF"
        android:fontFamily="sans-serif-light"
        android:padding="10dp"
        android:layout_margin="30dp"
        android:text="  ROHIT.K 🎊 "
        android:textColor="@color/teal_200"
        android:textSize="36sp" />

</RelativeLayout>

That's all for today!

References:

If you liked my content, plz do share
Also if you got any questions or suggestions feel free to comment down below .

If you are thinking of starting an Android Development you can check this blog,

What to Learn to get started with Android App Development?

ROHIT KUMAR ・ Jul 12 '21

#beginners #android #kotlin #java

Thank You! 😊

You can follow me on
Linkedin
Twitter

Android Basics: UI Layouts

ROHIT KUMAR — Tue, 27 Jul 2021 06:09:28 +0000

The entire content is inspired by ,
Google's udacity course Android Basics: User Interface. Its first part of the five parts Android Basics Nanodegree Program series , This course is for basics of Android and Java programming as , and take the first step on your journey to becoming an Android developer, you can learn more about this here.
So I would be writing a Blog series where I will cover everything that I have learned ,and explain it in easy way.

If you are thinking of starting an Android Development you can check this blog,

What to Learn to get started with Android App Development?

ROHIT KUMAR ・ Jul 12 '21

#beginners #android #kotlin #java

In this article,

We cover about the basic knowledge of how to place the layouts on the page to create image, text , button on the phone screen.

So without much late, let's get into topic..

We use XML (Xtensible Markup Language) to build Layout or define an UI in the Android app ,like TextView how to place and where to place something
This resource are always maintained separately in various sub-directories under res/ directory of the project.

What is Layout🤔

Every individual view make up what we call layout of the app of what the user sees on the screen.

The basic building block for user interface is a View object which is created from the View class and occupies a rectangular area on the screen and is responsible for drawing and event handling. View is the base class for widgets, which are used to create interactive UI components.

The ViewGroup is a subclass of View and provides invisible container that hold other Views or other ViewGroups and define their layout properties.

View

A rectangle on the screen that shows up in a piece of information or some content
It can be image text buttonor anything a app can display

⭕Some View attributes

android:id

View object may have a unique ID assigned to it which will identify the View uniquely. The syntax for an ID, inside an XML tag is
For assigning the View ID name

android:id="@+id/text_id"

For using its id name to as a reference

android:id="@id/text_id"

layout_width & layout_height

These are ViewGroup Layout Params
Its specifies the basic width & height of the view respectively.This is a required attribute for any view inside of a containing layout manager.

This is actually an attributes of ViewGroup and used by the view to tell there parent view how they want to be set

The attributes value may be a dimension (such as "12dp") which is hardcoded value or one of the special constants..

Attributes Value	Description
Hardcoded values	`px` (pixels), `dp` (density-independent pixels), `sp`(scaled pixels based on preferred font size), `in` (inches), and `mm` (millimeters)
MATCH_PARENT	which means the view wants to be as big as its parent (minus padding)
WRAP_CONTENT	which means that the view wants to be just big enough to enclose its content (plus padding)

     android:layout_width="match_parent"
     android:layout_height="wrap_content"

Density Independent Pixel (dp)

First lets know about what is Pixel❓

The one small dot or illuminated area on screen is called 1 pixel
Screens are made up of rows and columns of 1000' of these pixel.
Now,
Device can range in screen density which is numbers of pixel per inch are on the screen , Hences devices with are varies in low,medium, high and extra high resolution.
If we use pixel(px) as a unit it would appear very smaller on high resolution device as there screen density is more

So its better to use density independent pixel which is also a unit and are independent of pixel ,to achieve same physical size of Views , across of different screen densites .

Hardcoding❓

Its set if instructions given into the app we use to give the fixed value to the View attributes.
Its disadvantages is, its fixed we have to keep on updating according to the content .
Hence we should use some special constant like match_parent wrap_content which is flexible and set accordingly .

⭕Android UI Controls

There are number of UI controls provided by Android that allow you to build the graphical user interface for your app.

Sr.No.	UI Control	Description
1	TextView	This control is used to display text to the user
2	EditText	Its includes rich editing capabilities
3	AutoCompleteTextView	Its similar to `EditText` and shows a suggestions while the user is typing.
4	ImageView	To display image inside the view
5	Button	It clicked by the user to perform an action .
6	ImageButton	This shows a button with an image (instead of text) that can be pressed or clicked by the user.
7	CheckBox	An on/off switch that can be toggled by the user
8	ToggleButton	An on/off button with a light indicator.
9	RadioButton	The `RadioButton` has two states: either checked or unchecked.
10	RadioGroup	A `Radiogroup` is used to group together one or more `RadioButtons`.
11	TimePicker	Its enables users to select a time of the day, in either 24-hour mode or AM/PM mode.
12	DatePicker	Its enables users to select a date of the day
	And many more....

🔘 Now we will learn abouts some important Views and there attributes

1.TextView Attributes

android:text
Text to display.
android:textAllCaps
Present the text in ALL CAPS. Possible value either "true" or "false".
android:textSize

Size of the text. Recommended dimension type for text is "sp" for scaled-pixels (example: 15sp).

We use attributes values unit as sp here because its changes to with the preference of user for the font size, which is setting app of the Android devices

android:textStyle

Style (bold, italic, bolditalic) for the text. You can use or more of the following values separated by '|'.

normal - 0
bold - 1
italic - 2

android:password
Whether the characters of the field are displayed as password dots instead of themselves. Possible value either "true" or "false".
android:textColor
For setting the color of color of the text .

HexColor Code

Android has set of color defined byt not all ,hence from material design we can use color code called hex color code is given a specific hexadecimal digits start with "#" sign.
Eg:- #FF0000-> Red
#000000-> Black
#FFFFFF-> White ,etc

Similarly many more attributes you can check on documentation

<TextView
      android:id="@+id/text_id"
      android:layout_width="300dp"
      android:layout_height="wrap_content"
      android:text="Hello_world" 
      android:textAllCaps="true"
      android:textColor="@android:color/holo_blue_dark
      android:textSize="50sp"/>

2.ImageView Attributes

android:src Sets a drawable as the content of this ImageView. How to insert and image file ❓
- First of all download an image , save it somewhere in local
- Now, in the directories app/res/drawable ,we put here every images used in the app
- For placing here we have to right click on drawable folder, click on reveal in explorer
- Now, just drag and drop the image file here in the drawable folder
- Inside the ImageView use this attributes android:src to refer our image in the drawable folder
- @ is used for the referencing a resource in an android app, here drawable is the resource type, and then we write the filename of the specific image

android:src="@ drawable/image_name

There are many various other resources like static content that your code uses, such as bitmaps, colors, layout definitions, user interface strings, animation instructions, and more. These resources are always maintained separately in various sub-directories under res/ directory of the project.

 MyProject/
   app/
      manifest/
         AndroidManifest.xml
   java/
      MyActivity.java  
      res/
         drawable/  
            image_name.png  
         layout/  
            activity_main.xml
            info.xml
         values/  
            strings.xml

android:scaleType Controls how the image should be resized or moved to match the size of this ImageView. It has some constant attributes values Lets check some of its ,
- center Center the image in the view, but perform no scaling.
- centerCrop Its scales the image to fit, the bounds of the view And it also maintain the aspect ratio of the image so that it didn't get distorted and then it crop of the edges and centres the image .
Similarly Many more attributes you can check onDocumentation

 <ImageView
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
         android:scaleType="centerCrop"
         android:src="@drawable/image_name />

3.Button Attributes

Button, is a component which can be pressed or clicked by the user to perform an action. It has the same properties as a TextView, with a few Button specific properties. The main usage of the Button view is that whenever we click a button, we can set a method that will handle that specific button request and will carry out the necessary action.

Below there is XML, how to define a button view in your android application:

<Button
    android:id="@+id/button_id"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="Click me"
    android:textColor="@android:color/holo_blue_dark" />

public class MyActivity extends Activity {
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);

         setContentView(R.layout.content_layout_id);

         final Button button = findViewById(R.id.button_id);
         button.setOnClickListener(new View.OnClickListener() {
             public void onClick(View v) {
                 // Code Perform action on click
             }
         });
     }
 }

The above code is in activity class its creates an instance of View.OnClickListener and wires the listener to the button using setOnClickListener .

Therefore, whenever we press the button with id button_id, the above method is called which executes the code written in onClick(View) method

Using android:onClick attributes

We can also assign a method directly in the layout XML while defining the button using, android:onClick attribute

<Button
    android:id="@+id/button_id"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:text="Click Me"
    android:textColor="@android:color/holo_blue_dark"
    android:onClick="study" />

When user will click on the Button defined in the above layout xml file, then Android system will call study(View) method, defined in MainActivity.java file. In order for this to work, the method must be public and accept a View type as its only parameter.

public void study(View view) {

    //Perform action on click   
}

Similarly many more attributes you can check on documentation

ViewGroup

It is a root view ,but that big as it contain the other view inside itself .
It's called the parent view and the view inside its are called its child view of the view group ,can be TextView , Button , ImageView,etc.
The ViewGroup has also attributes ,such as layout_height, layout_width, background color ,etc.
We call it as a containers for the other views .

Types of ViewGroup

There are number of Layouts provided by Android which you will use in almost all the Android applications to provide different view, look and feel.
Some of them are ,

Linear Layout
LinearLayout is a view group that aligns all children in a single direction, vertically or horizontally.
Relative Layout
RelativeLayout is a view group that displays child views in relative to the parent or the other child view.
Table Layout
TableLayout is a view that groups views into rows and columns.
Frame Layout
The FrameLayout is a placeholder on screen that you can use to display a single view.
Constraint Layout
Constraint Layout allows us to create large and complex layouts with a flat view hierarchy, and also allows you to position and size widgets in a very flexible way.

That's all for today!

If you liked my content, plz do share
Also if you got any questions feel free to comment below .

If there was any mistake please do let me know, I'll correct it immediately.

Thank You! 😊

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What to Learn to get started with Android App Development?

ROHIT KUMAR — Mon, 12 Jul 2021 06:13:44 +0000

Yes!🤔 This question might confuse every beginner whenever they are thinking of to starting a new journey here.
So, if you’re one of those enthusiasts here's my article to help you getting started with android app development.

Choose a Platform

Mobile development is a broad field and therefore this means there are multiple ways to develop an application i.e this question has more than one answers. Basically the whole mobile development community works on two fronts, one is Native development and Cross-Platform development

Android development -> using Kotlin and Java
IOS development -> using Objective C and Swift
Cross-Platform -> using Flutter,Ionic,Xamarin,React-Native,etc
First two points is an example for Native and the Third one for Hybrid

By Native Development it means that is built for one specific platform. Hence written in languages compatible with the platform For instance, native Android app run on Android OS only Whereas native iOS apps run on iOS only.
With Cross-platform Development one's can write code once and run on different platforms. Hence specialized tools are taken into service, can run on both iOS and Android platforms.

For someone new to mobile development, its better to learn native first then move to cross-platform technologies( if you want to ),
As of now better hybrid technologies are React-Native and Flutter and to my understanding that to be good in these we need a pretty strong understanding on native mobile development.

So, keep this Native vs Cross-Platform for some others day topic
However this blog is focused in Native way of Android development

Learn a LANGUAGE

For the languages, you can develop android apps either by using Kotlin or Java, Hence another confusing part for beginners.
You need to learn basic of any programming language before getting started with android such as OOPS and other such underlying concepts

1.JAVA

Java was the first official programming language that is used to develop android apps.
The support community and user base is more in Java its older than Kotlin.
Android is the framework written in Java, so to code android android application you need to learn java and make yourself familiar with the syntax

2.KOTLIN

Launched by JetBrains, who created IntelliJ IDE and it too runs on JVM
Google in May 2017 announced Kotlin as the official language of Android App Development
Kotlin made android app development much easy as the length of the code had decreased than Java , and other such features
For a android developer Kotlin should be the language of choice nowadays

As time is changing the companies are shifting to Kotlin. Hence its most preferred since it offers a lot as compared to Java. Google also offers a lot of support to Kotlin, like many new Jetpack APIs and features will be offered first in Kotlin.

BUT for beginners in android with no experience with any line of codes or any other programming language first learn Android development inJava, then switch to Kotlin.

3.XML(Extensible Markup Language)

XML is important used to design UI/UX of an app its, presentation, layouts,etc
Since its markup language its work is to describes data and introducing elements like sets the layout of things like buttons and images, and defines the font, color, and any text.

To recap, XML describes the views in layout, and Java/Kotlin tells them how to behave.
Its not needed to learn in depth beforehand you can learn along the way.

ANDROID SDK

Android SDK stands for Android Software Development Kit which is developed by Google for Android Platform.
Android SDK is a collection of libraries and Software Development tools helps to create android Apps easily.
Its includes necessary utilities to help Android developers calling different APIs developed by Google both for controlling the device's functions and for integrating services
Component of the Android SDK such as Gradle,emulator,build tool,platform tool ,etc.

Using an IDE Android Studio

There are many IDE available for development,but
It’s unquestionably the best IDE (Integrated Development Environment) for Android
Android Studio is a must have for both the beginner and experienced Android developer.

Built on top of IntelliJ IDE,developed by Google for android application development.
Google on 16th May 2013 announced as a official IDE for Android app development.
Its comes with great out-of-the-box support for many of the most common Android SDKs.
It has advanced tools like memory monitors,CPU monitors,Code debuggers,Code completion,etc helping developers make sure their code will maintain high performance on a mobile device.

Start with android

After just understanding the basics of the above listed ,it is now time to get your hand dirty. Hence just install Android Studio and start developing an app, As Practice together along with theory is one of the best ways of learning.

One of the important skill as an android developer is of reading and searching for answer ,For development Android provides the most important and incredible documentation:-
Android Documentation

You won’t understand and remember everything for the first time, ones has to browse this sites millions time and each time you will become one step better version from your previous

Here's the link of bunch of resources you can go through
1.Android basics in Kotlin-Free course by Google , you'll learn the basics of building Android apps with the Kotlin.
2.Developing Android Apps with Kotlin - Its an Udacity course by
Google.
3.Android Basics: User Interface -Learn the basics of Android and Java programming this courses doesn't require any prior knowledge in coding. One with no experience with any lines of code can also start here
4.Android codelabs - Its practical codelabs course by Google,finds a lot of helpful examples.

SOMETHING MORE

NOW ,this section is once you have started Android development and getting familiar, too with some Techincal terms
List of some important terms which you will find along the way -

1.Understand Material Designs

Google has released a set of forward-thinking interface guidelines and standards called Material Design, to help build consistent and high quality app UI and give aesthetic look .
These standards include tips for how to layer various elements on the screen and use specific styles and highlights the best practices for we can use
Try to feel it. Be the material. Think like material. Behave like material. You shouldn’t miss this point while getting started with Android.

2.Gradle build

Gradle is another build system that takes the best features from other build systems and combines them into one.
“Build.gradle” are scripts where one can automate the tasks.
For example, the simple task to copy some files from one directory to another can be performed by Gradle build script before the actual build process happens.
Every Android project needs a gradle for generating an apk from the .java and .xml files in the project.

3.Learn Version Control

There are multiple Version Control Systems available but Git is the most common one these days.
These are tools that enables you to keep your code and also track your progress.
Resource for learning Version Control with Git
Showcasing your project you can learn and build the portfolio on github

5. AND there is many more

like for Database connectivity Firebase is there
you’ll likely want to interact with many other services through APIs Jetpack libraries are there.

This list don't ends here ,
When one picks up a career in tech they commit themselves to lifelong learning, and one thing for sure you will love it , as these technologies there only to help you and make your app developing process easier.

Now here providing the flowchart-

Remember to not be exhausted by the list, just learn the basics and start working on some project, rest of the learnings will come along the way. Good luck!

Reference -
- Essential Skill
- Compelete roadmap , here you will find resources link of other important part in android

Personal Tips -If you want to start then, one of the best habits is that start reading articles regarding the application development.

Now we came to an end of the article
I hope you found this article valuable. If yes do let me know in the comments 😊

THANK YOU!

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Create an executable JAR file on VS Code n Command line

ROHIT KUMAR — Mon, 28 Jun 2021 18:29:26 +0000

So what exactly is JAR?

The Jar (Java Archive) tool of JDK used to package one or more Java class files and associated metadata and resources (text, images, etc.) into one file to distribute application software or libraries on the Java platform ~~And~~ it provides the facility to create the executable jar file which calls the main method of the class if you double click it.

Simply speaking, this is a format for archiving data. This is similar to you using WinRAR or WinZIP.
You can read Oracle documentation on jar here

In this article,

We will learn how to create an executable jar file, we will take a Java application and explore two ways to run it as a jar, just by double clicking on it. Using VsCode & Command line

What does it mean when we say that the file is an executable JAR file?
Well, when you double click on the JAR file, it automatically calls the main method of the program And if program have JAVA GUI such as frames, panel present inside the main method, that would also be executed.

VisualStudioCode

VS Code is a more flexible IDE in today’s competition, so its important to know to create jar file here which will get our job done faster with ease.

If you want to learn more about VsCode and other text editors you can go through this Blogpost

Best IDE’s and Text Editors!

KUMAR HARSH ・ Jun 24 '21

#productivity #programming #codenewbie

NOW, Follow the following steps:-

1.Download the extension

In VsCode marketplace install extension Java Extension Pack which includes set of extensions needed for configuring java enviroment in vscode or you can just download Project Manager for Java extension which is just needed here

2.Write your Java program

I am using my java code of calculator ,a gui application using AWT
NOTE:-application needs to have a class with a main method. This class provides our entry point into the application

3.Export jar file

In order to compile the code by packing JAR inside Vscode, at bottom left corner you will find and option JAVA PROJECTS there you will find and symbol saying EXPORT JAR. Click it

IMP: now its a very important task it will ask you to specify main class just provide the main class ,here MyCalc
this class provide the entry point so its important to mention.

NOTE:-Otherwise the jar file will become, normal jarfile not an executable ones

NOW ENJOY your EXECUTABLE JAR FILE has been created ,here CALC.jar you can go to your directories and just double click it or choose and option ,open with JAVA(TM) Platform SE Binary

Command line

NOW using command line you should know the jar tool ,provides certain switches with which we can create an executable jarfile
some of them are as follows:

c creates new archive file

v generates verbose output. It displays the included or extracted resource on the standard output.

m includes manifest information from the given mf file.

f specifies the archive file name

x extracts files from the archive file

Write the java file and then and then follow the following step:-

1.Compile java code

We can do this with javac from the command line:

javac MyCalc.java

The javac command creates MyCalc.class in the current directory. If you have multiple java file compile them too, We can now package that into a jar file.

2.Creating manifest file

A manifest file is essential as it sets an entry points,to our application which main class that we are going to execute to the jarfile.
So, Create a manifest file with .MF extensions in same directories ,so that not needed to set class path explicitly
You need to write Main-Class, then colon, then space, then classname which you want to make an entry point (here MyCalc) then press enter.

NOTE:It's important that we end our manifest file with a newline.Otherwise ~~no main manifest attribute~~ error is thrown.

now save the .MF file here manifest.MF

3.Creating the executable jar

Open the Command Prompt, write the command using jar tool switches provided
using jar command

jar -cvfm <jarfilename.jar> <manifestfile> <classname.class>

Command order shouldn't be change
1.jar command to create a jar file.
2.switchc used to indicates we are creating new file
3.switchv generates verbose output information
4.switchf tell about the jarfile name we are creating
5.switchm it includes the manifest information
Hence, the corresponding filename are also written in the same order ,and if there is multiple class files, then include them too.

example

4.Running the Jar

NOW ,we can use the -jar option of the java command to run our application since executable jarfile has been created.

java -jar CALC.jar

here I named my jarfile as CALC.jar
now our application will be executed after this command

OR
You can run this, just by DOUBLE CLICKING as our main motive of making our jar file executable.

And that's it. Now you can also run your jarfile with an ease just by clicking it.
If you would like to download & run my CALC.jar you can find here
as to show how one can easily share ,justifying its properties that import anywhere it is required.
AND

You can check my Blogpost where I had explained how I created this basic calculator using java AWT

Creating a Calculator using Java AWT

ROHIT KUMAR ・ Jun 18 '21

#java #programming #tutorial #guiapplication

With this I will end my articles here,
Hope you all find it valuable, and if you have any doubt ,then you ask me just by commenting below.

If the program runs, you're done! Happy coding!

Thank You!

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Creating a Calculator using Java AWT

ROHIT KUMAR — Fri, 18 Jun 2021 15:11:48 +0000

In this Java tutorial,

We will learn how to build a simple calculator using Java AWT. This calculator has some simple functionality like all the basic mathematical operations and some special addon features , we will see as we follow
So let’s get started
FIRST of all small description on AWT
AWT(Abstract Window Toolkit) is an API that helps in building GUI (Graphical User Interface) based java applications. GUI helps in user interactions using some graphics. It primarily consists of a set of classes and methods that are required for creating and managing the GUI in a simplified manner such as buttons,windows,frame,textfield,RadioButton etc
I have provided the Java code for the calculator which uses Action listener interface for EventHandling.
And yes its not an applet code, which is deprecated



import java.awt.*;  
import java.awt.event.*;  
class MyCalc extends WindowAdapter implements ActionListener{ 
  Frame f; 
Label l1;
Button b1,b2,b3,b4,b5,b6,b7,b8,b9,b0;
Button badd,bsub,bmult,bdiv,bmod,bcalc,bclr,bpts,bneg,bback;
double xd;
double num1,num2,check;

MyCalc(){  
  f= new Frame("MY CALCULATOR");
// INSTANTIATING COMPONENETS 
l1=new Label(); 
l1.setBackground(Color.LIGHT_GRAY);
l1.setBounds(50,50,260,60);


b1=new Button("1");
  b1.setBounds(50,340,50,50);
b2=new Button("2");
  b2.setBounds(120,340,50,50);
b3=new Button("3");
  b3.setBounds(190,340,50,50);
b4=new Button("4");
  b4.setBounds(50,270,50,50);
b5=new Button("5");
  b5.setBounds(120,270,50,50); 
b6=new Button("6");
  b6.setBounds(190,270,50,50);
b7=new Button("7");
  b7.setBounds(50,200,50,50);
b8=new Button("8");
  b8.setBounds(120,200,50,50);
b9=new Button("9");
  b9.setBounds(190,200,50,50);
b0=new Button("0");
  b0.setBounds(120,410,50,50);
bneg=new Button("+/-");
  bneg.setBounds(50,410,50,50);
bpts=new Button(".");
  bpts.setBounds(190,410,50,50);
bback=new Button("back");
 bback.setBounds(120,130,50,50);

badd=new Button("+");
  badd.setBounds(260,340,50,50);
bsub=new Button("-");
  bsub.setBounds(260,270,50,50);
bmult=new Button("*");
  bmult.setBounds(260,200,50,50);
bdiv=new Button("/");
  bdiv.setBounds(260,130,50,50);
bmod=new Button("%");
  bmod.setBounds(190,130,50,50);
bcalc=new Button("=");
  bcalc.setBounds(245,410,65,50);
bclr=new Button("CE"); 
  bclr.setBounds(50,130,65,50);


b1.addActionListener(this); 
b2.addActionListener(this);  
b3.addActionListener(this);  
b4.addActionListener(this);  
b5.addActionListener(this); 
b6.addActionListener(this); 
b7.addActionListener(this); 
b8.addActionListener(this); 
b9.addActionListener(this);  
b0.addActionListener(this);

bpts.addActionListener(this);  
bneg.addActionListener(this);
bback.addActionListener(this); 

badd.addActionListener(this);
bsub.addActionListener(this);
bmult.addActionListener(this);
bdiv.addActionListener(this);
bmod.addActionListener(this);
bcalc.addActionListener(this);
bclr.addActionListener(this); 

f.addWindowListener(this);
//ADDING TO FRAME   
f.add(l1);  
f.add(b1); f.add(b2); f.add(b3); f.add(b4); f.add(b5);f.add(b6); f.add(b7); f.add(b8);f.add(b9);f.add(b0);

f.add(badd); f.add(bsub); f.add(bmod); f.add(bmult); f.add(bdiv); f.add(bmod);f.add(bcalc);

f.add(bclr); f.add(bpts);f.add(bneg); f.add(bback);

f.setSize(360,500);  
f.setLayout(null);  
f.setVisible(true);  
} 
                     //FOR CLOSING THE WINDOW
public void windowClosing(WindowEvent e) {
  f.dispose();
}

public void actionPerformed(ActionEvent e){ 
  String z,zt;
                        //NUMBER BUTTON 
if(e.getSource()==b1){
 zt=l1.getText();
  z=zt+"1";
  l1.setText(z);
}
if(e.getSource()==b2){
zt=l1.getText();
z=zt+"2";
l1.setText(z);
}
if(e.getSource()==b3){
  zt=l1.getText();
  z=zt+"3";
  l1.setText(z);
}
if(e.getSource()==b4){
  zt=l1.getText();
  z=zt+"4";
  l1.setText(z);
}
if(e.getSource()==b5){
  zt=l1.getText();
  z=zt+"5";
  l1.setText(z);
}
if(e.getSource()==b6){
  zt=l1.getText();
  z=zt+"6";
  l1.setText(z);
}
if(e.getSource()==b7){
  zt=l1.getText();
  z=zt+"7";
  l1.setText(z);
}
if(e.getSource()==b8){
  zt=l1.getText();
  z=zt+"8";
  l1.setText(z);
}
if(e.getSource()==b9){
  zt=l1.getText();
  z=zt+"9";
  l1.setText(z);
}
if(e.getSource()==b0){
  zt=l1.getText();
  z=zt+"0";
  l1.setText(z);
}

if(e.getSource()==bpts){  //ADD DECIMAL PTS
  zt=l1.getText();
  z=zt+".";
  l1.setText(z);
}
if(e.getSource()==bneg){ //FOR NEGATIVE
  zt=l1.getText();
  z="-"+zt;
  l1.setText(z);
}

if(e.getSource()==bback){  // FOR  BACKSPACE
  zt=l1.getText();
  try{
    z=zt.substring(0, zt.length()-1);
    }catch(StringIndexOutOfBoundsException f){return;}
  l1.setText(z);
}
                //AIRTHMETIC BUTTON
if(e.getSource()==badd){                     //FOR ADDITION
  try{
    num1=Double.parseDouble(l1.getText());
    }catch(NumberFormatException f){
      l1.setText("Invalid Format");
      return;
    }
  z="";
  l1.setText(z);
  check=1;
}
if(e.getSource()==bsub){                    //FOR SUBTRACTION
  try{
    num1=Double.parseDouble(l1.getText());
    }catch(NumberFormatException f){
      l1.setText("Invalid Format");
      return;
    }
  z="";
  l1.setText(z);
  check=2;
}
if(e.getSource()==bmult){                   //FOR MULTIPLICATION
  try{
    num1=Double.parseDouble(l1.getText());
    }catch(NumberFormatException f){
      l1.setText("Invalid Format");
      return;
    }
  z="";
  l1.setText(z);
  check=3;
}
if(e.getSource()==bdiv){                   //FOR DIVISION
  try{
    num1=Double.parseDouble(l1.getText());
    }catch(NumberFormatException f){
      l1.setText("Invalid Format");
      return;
    }
  z="";
  l1.setText(z);
  check=4;
}
if(e.getSource()==bmod){                  //FOR MOD/REMAINDER
  try{
    num1=Double.parseDouble(l1.getText());
    }catch(NumberFormatException f){
      l1.setText("Invalid Format");
      return;
    }
  z="";
  l1.setText(z);
  check=5;
}
                         //RESULT BUTTON
if(e.getSource()==bcalc){          
  try{
    num2=Double.parseDouble(l1.getText());
    }catch(Exception f){
      l1.setText("ENTER NUMBER FIRST ");
      return;
    }
  if(check==1)
    xd =num1+num2;
  if(check==2)
    xd =num1-num2;
  if(check==3)
    xd =num1*num2;
  if(check==4)
    xd =num1/num2; 
  if(check==5)
    xd =num1%num2;    
  l1.setText(String.valueOf(xd));
}
                        //FOR CLEARING THE LABEL and Memory
if(e.getSource()==bclr){
  num1=0;
  num2=0;
  check=0;
  xd=0;
   z="";
   l1.setText(z);
   } 

}  
//MAIN METHOD where objects of MyCalc is instantaiated
 public static void main(String args[]){  
       new MyCalc();  
   }
}

SO what I did is just implemented ActionListenerinterface in our MyCalc class and in its constructor i Register the AWT components with the Listener and done EventHandling using actionPerformed method.
OUR all the logic part in written in this actionPerformed function only which we will see below:

LOGIC PART

1.FOR NUMERIC BUTTON



if(e.getSource()==b1){ //b1 for number 1
 zt=l1.getText();
  z=zt+"1";// 1 will merged at the end of the previous value
  l1.setText(z);
}

when any of the numeric button pressed
whatever value in label l1 will be stored in a variable zt and then concatenated with the corresponding number and and then displayed in the label l1
for NEGATIVE and DECIMAL PTS Button we did it similarly

2.FOR AIRTHMETIC BUTTON



if(e.getSource()==badd){  //FOR ADDITION
    num1=Double.parseDouble(l1.getText());
  z="";
  l1.setText(z);
  check=1; // 1 for the adddition
}

NOW here we store the value of label l1 into a variable num1 after converting into double type which will be technically 1st number
and then and set label l1 to null

we will just use a check variable for getting that this particular airthmetic button(here +) was clicked so we can do this operation in our = button

3.FOR EQUALS BUTTON



if(e.getSource()==bcalc){          
    num2=Double.parseDouble(l1.getText());
  if(check==1)
    xd =num1+num2;
  if(check==2)
    xd =num1-num2;
  if(check==3)
    xd =num1*num2;
  if(check==4)
    xd =num1/num2; 
  if(check==5)
    xd =num1%num2;    
  l1.setText(String.valueOf(xd));
}

NOW again store the value of l1 into num2 variable which will be techincally 2nd number
and then check the value of variable check and then do corresponding operation and after that display result in label l1

4.FOR CLEAR BUTTON



 if(e.getSource()==bclr){
  num1=0;
  num2=0;
  check=0;
  xd=0;
   z="";
   l1.setText(z);
   }

here updated all the variable we use to its Default value 0
and set label l1 to null so that we can start our new calculation afterward

5.FOR BACKSPACE BUTTON



 if(e.getSource()==bback){  // FOR  BACKSPACE
  zt=l1.getText();
  try{
    z=zt.substring(0, zt.length()-1);
    }catch(StringIndexOutOfBoundsException f){return;}
  l1.setText(z);
}

here just updates the value in l1 by removing last digits using substring function
and handled one StringIndexOutOfBoundsException which occur when our value in label is null and still pressing back Button

6.SPECIAL ADDONS FEATURE

what I did is just handled one execption in EQUAL and all AIRTHMETIC Buttons and printed a desired message according to situtation
inside AIRTHMETIC BUTTONS:



try{
    num1=Double.parseDouble(l1.getText());
    }catch(NumberFormatException f){
      l1.setText("Invalid Format");
      return;
    }

inside EQUALS BUTTON:



try{
    num2=Double.parseDouble(l1.getText());
    }catch(Exception f){
      l1.setText("ENTER NUMBER FIRST ");
      return;
    }

when we was converting the value into the double value, BUT lets say that, label l1 has null value (i.e. label is empty) and we still pressed these button then it will generate NumberFormatException execption,
So handled that and printed desired message
For eg:
If I click1 then + and then i click - instead of some other numeric button, hence this an invalid format, and when -was clicked at that time label was null hence execption generated so just handled it and printed invalid format inlabel

SIMILARLY, when label is null,and = was clicked in that situation ENTER NUMBER FIRST will be displayed inside label

With this, we come to an end of this Java AWT Tutorial.
So just go through the code and try it. If you have any difficulty in understanding or using the code, then you ask by commenting below.
If you would like to download & run my CALC you can find here
I have uploaded both source code & executable jarfile

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