DEV Community: Hamid Mohamadi

Lesson 8 : Java Control Statements (part 2) :

Hamid Mohamadi — Mon, 01 Jul 2019 18:33:34 +0000

We discussed about "selection or conditional statements" in the last post . Now , let's continue :
The second category in java statements is :

2- Iteration or Looping statements :

( for , while , do-while )

In iteration statements, the same code fragment execute several times until a specific condition is satisfied . Iteration statement executes the same set of instructions until a termination condition is met .
for :
A for loop executes a statement ( that is usually a block ) as long as the boolean condition evaluates to true . A for loop is a combination of the three elements initialization statement ( or it can be any valid java statement , boolean expression and increment or decrement statement .

You can try examples here.

while :
A while loop statement in Java programming language repeatedly executes a target statement as long as a given condition is true.

You can try examples here.

do-while loop :
A do...while loop is similar to a while loop, except that a do...while loop is guaranteed to execute at least one time.

You can try examples here.

3- Jump Statements:

In Java jump statements are mainly used to transfer control to another part of our program depending on the conditions. These statements are very useful from the programmer's view because these statements allow alteration of the flow of execution of the program. These statements can be used to jump directly to other statements, skip a specific statement and so on. In Java we have the following three jump statements:

1- break (simple and labeled)
2- continue
3- return

The break statement :
If we want to go out of a loop then we use a break statement. If we use a break statement in a loop then execution will continue with the immediate next statement outside the loop. After a break, all the remaining statements in the loop are skipped. The break statement can be used in a while loop, for loop, do-while loop, and in a switch case.
Syntax :
if(condition)
{
break;
}

The continue statement :
The continue keyword is used mainly with loops. When we do not want to execute some statements then we use a continue statement to skip those statements to execute. If the continue statement is confronted in the program then it will start the next iteration. It does not terminate the loop, it just skips some part of the loop. The execution again starts from the top of the loop. In some ways it is similar to the break statement.
Syntax :
if(condition)
{
continue;
}

The return statement :
The return statement is the last jump statement. The return statement is used to end the execution of a specific method and then return a value. When we use a return statement in our program then it sends the program control to the method caller. The data type of the returned value should always be equal to the data type of the method's declared return value.
Syntax :
if(condition)
{
return;
}

Lesson 7 : Java Control Statements (part 1) :

Hamid Mohamadi — Sat, 22 Jun 2019 19:54:33 +0000

A program normally executes from top to bottom except when we use control statements, we can control the order of execution of the program, based on logic and values.
In Java, control statements can be divided into the following three categories:

1- Selection or conditional statements :

Selection statements allows us to control the flow of program execution on the basis of the outcome of an expression :

(if , if - else , if - else - if , nested if-else , switch)

if :
if statement is the most simple decision making statement. It is used to decide whether a certain statement or block of statements will be executed or not i.e if a certain condition is true then a block of statement is executed otherwise not.

You can try examples here .

if-else :

The if statement alone tells us that if a condition is true it will execute a block of statements and if the condition is false it won’t. But what if we want to do something else if the condition is false. Here comes the else statement. We can use the else statement with if statement to execute a block of code when the condition is false.

You can try examples here .

if-else-if :

Here, a user can decide among multiple options. The if statements are executed from the top down. As soon as one of the conditions controlling the if is true, the statement associated with that if is executed, and the rest of the ladder is bypassed. If none of the conditions is true, then the final else statement will be executed.

You can try examples here .

nested if-else :

in nested if-else we can use one if statement inside another if or else if statement .

switch :

The switch statement is a multi-way branch statement . It defines multiple paths of execution of a program . It provides a better alternative than a large series of if-else-if statement .

You can try examples here .

Lesson 6 : Literals , Keywords and Identifiers

Hamid Mohamadi — Sat, 15 Jun 2019 19:53:50 +0000

Literal is the value assigned to a variable :

Literals categories :

- Integer literals

- String literals

- Boolean literals

- Character literals

- Float literals

- Null literals

Keywords :

Keywords are the predefined words having any specific meanings :

Identifiers :

Identifier is any name , it can be a variable name , class name or method name :

Rules for Identifiers :

1- space can not be used :

int emp no = 10 ; ---------> int emp_no = 10 ;

2- only underscore( _ ) and dollar ( $ ) can be used :

int emp_no = 10 ;

3- Reserved word can not be used :

int public = 10 ; ----------> int a = 10 ;

4- Integer values can not be used at first position but it can be used after first character :

int 1abc = 10 ; -----> int a1bc = 10 ; int abc1 = 10 ;

Naming Conventions :

variable -----------> my , my_java , my_java_demo

methods----------> my() , myJava() , my java demo()

class/interface----> My , MyJava , MyJavaDemo

Lesson 5 : Operators In Java

Hamid Mohamadi — Sat, 15 Jun 2019 08:05:15 +0000

Operators are the special symbols which perform any operation on one or more operands :

1- Arithmetic operators :

2- Assignment operators :

3- Comparison operators :

4- Logical operators :

5- Bitwise operators :

Lesson 4 : Variables In Java

Hamid Mohamadi — Thu, 13 Jun 2019 11:21:04 +0000

A Java variable is a piece of memory that can contain a data value . A variable thus has a data type . Variables are typically used to store information which your Java program needs to do it's job .

Variables :

1- local

2- instance

3- static

Variables have some attributes that you can see in the picture below :

Notice the example below that use static and instance variables :

Lesson 3 : Data Types In Java

Hamid Mohamadi — Wed, 12 Jun 2019 10:34:02 +0000

you see in the picture above , the categories of data types in Java . But , don't worry , you will learn to use all of them .

Lesson 2 : Getting Started With Java

Hamid Mohamadi — Tue, 11 Jun 2019 13:55:24 +0000

If we have liken the process of Java as a tree , we will have the following image :

So , let's start programming :

First of all , it's better to learn about JVM , JRE , JDK , and IDE :

1. JVM :

A Java virtual machine is the core of Java . It's a virtual machine that enables a computer to run Java programs as well as programs written in other languages that are also compiled to Java bytecode.

2. JRE :

It is the most common Java environment installed on personal computers in the laptop and desktop from factors . Mobile phones including features and smartphones that ship with a JVM are most likely to include a JVM meant to run applications .

3. JDK :

simply , JDK is an implementation for Java programs .
The JDK includes a private JVM and a few other resources to finish the development of a Java application .

4. IDE :

An integrated development environment (IDE) is a software application that provides comprehensive facilities to computer programmers for software developments . like IntelliJ , Netbeans , Eclipse , ... .

Lesson 1 : Introduction

Hamid Mohamadi — Mon, 10 Jun 2019 10:20:30 +0000

A programming language is a formal computer language designed to communicate instruction to a machine , particularly a computer . Programming languages can be used to create programs or algorithms to control the behavior of the machine .

Java :
Java is a programming language that is class-based and object-oriented . Java was originally developed by "James Goseling" in 1995 .
Java is used to develop mobiles app , web apps , desktop apps , games and much more .

Why Java ?
Java is popular :

In the top 3 (if not the most popular)
3 billion devices run
Platform independency (write once , run anywhere )
wide usability
very well paying jobs