DEV Community: Emmanuel Ogbinaka

The Java `.boxed()` Method

Emmanuel Ogbinaka — Sun, 19 Jun 2022 14:56:16 +0000

In this post I'll be talking about the boxed() method of Java streams.

What is the `boxed()` method?

The method boxed() is designed only for streams of some primitive types (IntStream, DoubleStream, and LongStream) to box each primitive value of the stream into the corresponding wrapper class (Integer, Double, and Long respectively).
[source][https://stackoverflow.com/a/47126809]

what this means is that whenever we use any of the primitive generators the generated values are corresponding primitives to the stream. that is :

IntStream - int
LongStream - long
DoubleStream - double

Although, we can perform intermediary operations on the generated values but we cannot perform some terminal operations on the generated values.

for example,
Generate a list of numbers from 1 to 100.

List<Integer> numbers = IntStream.rangeClosed(1 , 100).collect(Collectors.toList());

The above operation will throw a compile time exception of
_ java.util.function.BiConsumer )' in 'java.util.stream.IntStream' cannot be applied to '(java.util.stream.Collector ?>,java.util.List >)'_

This is where the .boxed() method comes in.
Notice the generic List uses the wrapper class for the primitive int type. What the .boxed() method does is that it returns a Stream consisting of the elements of the given stream, each boxed to an object of the corresponding wrapper class.

Or simply put, the .boxed() method puts each value in the stream in its corresponding wrapper class.

IntStream.boxed() - Integer
LongStream.boxed() - Long
DoubleStream.boxed() - Double

So a good solution to the example problem is:

List<Integer> numbers = IntStream.rangeClosed(1 , 100).boxed().collect(Collectors.toList());

Hope you find this info useful. Thanks.

Loading Initial Data with Spring Boot

Emmanuel Ogbinaka — Mon, 23 Aug 2021 23:08:30 +0000

With SpringBoot + Hibernate we can easily manage our database. By default, all classes marked with the @Entity annotation in our packages are used to create tables automatically.

Well, there are times we need more fine-grained control over the database alterations according to our requirements.
In this post I'll be sharing lights on one of those scenarios: Auto-populating or loading initial values into our tables.

SpringBoot has some reservations for situations as this. We make use of the data.sql file in Spring to actualise this.

This file should be saved in the directory:
src/main/resources/

Hint: Same location as application.properties file.

When we run the project with this file on the resources directory, Spring will pick it up and use it for populating the database.

As an example, we can decide to load initial values for the Role entity as follows:

INSERT INTO Role (name) VALUES ('USER');
INSERT INTO Role (name) VALUES ('ADMIN');

When you start your application, spring will attempt to load these data into the Role table which at this time does not exist which will cause the program to fail, so we need to add the following config to application.properties file

spring.jpa.defer-datasource-initialization=true

This tells spring to delay the data initialisation process. Now start your spring application, and you should be able to see the values 'USER' & 'ADMIN' in the Role table.

Hope you find this helpful. You can leave a comment to contribute. Thanks!

Auto-Reload SpringBoot in IntelliJ IDEA

Emmanuel Ogbinaka — Tue, 10 Aug 2021 11:49:34 +0000

Having to click on the Re-run to restart your Springboot application after making changes can get tiring at some point.

Please note, the spring-dev-tools provides this functionality out-of-the-box, but couldn't get to make it work for myself. So, in this post I'll show how I hacked my way around it.

The first step is to add the Spring-dev-tools dependencies to your project pom.xml file within the tag.
NB: This is a key component for this to work

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-devtools</artifactId>
    <scope>runtime</scope>
    <optional>true</optional>
</dependency>

By this I believe your IDE (IntelliJ) is open;
Open the IDE preferences by using the shortcut cmd + , for macs from your keyboard or from the menu bar click on IntelliJ Menu >> Preferences. This will open the Preferences dialog.

On the left pane, click on the Build, Execution, Deployment option to reveal it's sub-menus. Click on Compiler and on the right check the Build Project Automatically option and click ok;

Double tap on the Shift key on your keyboard to open IntelliJ search dialog and type registry to open the registry settings.

Find compiler.automake.allow.when.app.running option and check it true; then restart your Spring-boot application and enjoy. Now upon any change in your source code spring restarts the application. Hope you find this helpful, Cheers!

How to Copy Array in Java

Emmanuel Ogbinaka — Mon, 09 Aug 2021 16:17:35 +0000

So you have two arrays A and B, and you need to copy the elements of A into B. Well there are various ways you can do this in Java and in this post I'll be showing you a couple of ways you can.

Method One : ForLoop
This good old for-loop to the rescue:

int[] A = {1,2,4,4};
int[] B = new int[];

 for (int i = 0; i < A.length; i++){
      B[i] = A[i];
}

Method Two : .clone()
The clone method of array can help you simply achieve this.

Usage

int[] A = {1,2,4,4};
int[] B = A.clone();//the clone method copies the content of A into B;

Method Three : System.arraycopy()
The next option is to use System.arraycopy() method present in the java.lang package. Before we get into it's usage, let's discuss it's signature:

public static void arraycopy(
    Object src, //:source array, in this case A
    int srcPos, //:the start index for copy, typically 0
    Object dest, //:destination object in this case B. 
    int destPos, //:the index to place the copied elements
    int length //:the length of the contents to be copied
);

Usage

int[] A = {1,2,4,4};
int[] B = new int[];

System.arraycopy(A, 0, B, 0, A.length);

Method Four : Arrays.copyOf()
The next option we'll be discussing is from the Arrays class present in the java.utils package. Once again, let's discuss it's signature:

public static int[] copyOf( 
    int[] original, // :source array in this case A
    int newLength // :the length of the contents to be copied
);

Usage

int[] A = {1,2,4,4};
int[] B = Arrays.copyOf(A, 3);

Method Five : Arrays.copyOfRange()
So, this will be the last option we'll be discussing for this post and from the Arrays class present in the java.utils package. Once again, let's see it's signature:

public static int[] copyOfRange(
    int[] original, // :source array in this case A
    int from,  //:the start index for copy, typically 0
    int to // the end index exclusive
);

Usage

int[] A = {1,2,3,4,5,6,7};
int[] B = Arrays.copyOfRange(A, 0, A.length);

DEV Community: Emmanuel Ogbinaka

The Java `.boxed()` Method

What is the boxed() method?

Loading Initial Data with Spring Boot

Auto-Reload SpringBoot in IntelliJ IDEA

How to Copy Array in Java

Usage

Usage

Usage

Usage

What is the `boxed()` method?