Creating library in java

Building Java Libraries Sample

This guide demonstrates how to create a Java library with Gradle using gradle init . You can follow the guide step-by-step to create a new project from scratch or download the complete sample project using the links above.

What you’ll build

You’ll generate a Java library that follows Gradle’s conventions.

What you’ll need

• A text editor or IDE — for example IntelliJ IDEA
• A Java Development Kit (JDK), version 8 or higher — for example AdoptOpenJDK
• The latest Gradle distribution

Create a project folder

Gradle comes with a built-in task, called init , that initializes a new Gradle project in an empty folder. The init task uses the (also built-in) wrapper task to create a Gradle wrapper script, gradlew .

The first step is to create a folder for the new project and change directory into it.

Run the init task

From inside the new project directory, run the init task using the following command in a terminal: gradle init . When prompted, select the 3: library project type and 3: Java as implementation language. Next you can choose the DSL for writing buildscripts — 1 : Groovy or 2: Kotlin . For the other questions, press enter to use the default values.

The output will look like this:

$ gradle init Select type of project to generate: 1: basic 2: application 3: library 4: Gradle plugin Enter selection (default: basic) [1..4] 3 Select implementation language: 1: C++ 2: Groovy 3: Java 4: Kotlin 5: Scala 6: Swift Enter selection (default: Java) [1..6] 3 Select build script DSL: 1: Groovy 2: Kotlin Enter selection (default: Groovy) [1..2] 1 Select test framework: 1: JUnit 4 2: TestNG 3: Spock 4: JUnit Jupiter Enter selection (default: JUnit 4) [1..4] Project name (default: demo): Source package (default: demo): BUILD SUCCESSFUL 2 actionable tasks: 2 executed

The init task generates the new project with the following structure:

├── gradle (1) │ └── wrapper │ ├── gradle-wrapper.jar │ └── gradle-wrapper.properties ├── gradlew (2) ├── gradlew.bat (2) ├── settings.gradle.kts (3) └── lib ├── build.gradle.kts (4) └── src ├── main │ └── java (5) │ └── demo │ └── Library.java └── test └── java (6) └── demo └── LibraryTest.java

├── gradle (1) │ └── wrapper │ ├── gradle-wrapper.jar │ └── gradle-wrapper.properties ├── gradlew (2) ├── gradlew.bat (2) ├── settings.gradle (3) └── lib ├── build.gradle (4) └── src ├── main │ └── java (5) │ └── demo │ └── Library.java └── test └── java (6) └── demo └── LibraryTest.java

1	Generated folder for wrapper files
2	Gradle wrapper start scripts
3	Settings file to define build name and subprojects
4	Build script of lib project
5	Default Java source folder
6	Default Java test source folder

You now have the project setup to build a Java library.

Review the project files

The settings.gradle(.kts) file has two interesting lines:

rootProject.name = "demo" include("lib")

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How to create my own java library(api)?

Creating your own Java library, or API, is a great way to reuse code and share functionality with others. By creating a Java library, you can package your code into a reusable and easily consumable form. In this way, other developers can easily integrate your library into their projects and benefit from the functionality you have provided.

Method 1: Create a Java project

Creating a Java library is a great way to organize your code and make it reusable. In this tutorial, we will go through the steps to create a Java library using a Java project.

Step 1: Create a Java Project

The first step is to create a Java project in your favorite IDE. For this tutorial, we will use Eclipse. Follow the steps below to create a new Java project:

1. Open Eclipse and click on «File» > «New» > «Java Project».
2. Enter a name for your project and click «Finish».

Step 2: Create a Package

The next step is to create a package for your library. A package is a way to organize your classes and interfaces. Follow the steps below to create a new package:

1. Right-click on your project and select «New» > «Package».
2. Enter a name for your package and click «Finish».

Step 3: Create Your Classes

Now it’s time to create your classes. A class is a blueprint for creating objects. Follow the steps below to create a new class:

1. Right-click on your package and select «New» > «Class».
2. Enter a name for your class and click «Finish».
3. Add your methods to your class. Here is an example:

package com.example.library; public class MyLibrary  public static int add(int a, int b)  return a + b; > >

Step 4: Export Your Library

The final step is to export your library as a JAR file. A JAR file is a package file format used to aggregate many Java class files and associated metadata and resources into one file. Follow the steps below to export your library:

1. Right-click on your project and select «Export».
2. Select «Java» > «JAR file» and click «Next».
3. Select the classes you want to include in your library and click «Next».
4. Enter a name for your JAR file and click «Finish».

Congratulations! You have now created your own Java library. You can use this library in other Java projects by adding the JAR file to your project’s classpath. Here is an example:

import com.example.library.MyLibrary; public class Main  public static void main(String[] args)  int result = MyLibrary.add(2, 3); System.out.println(result); // Output: 5 > >

In this example, we import the MyLibrary class from our library and use the add method to add two numbers. The result is then printed to the console.

Method 2: Package your code into a library

Step 1: Create a new Java Project

First, create a new Java project in your favorite IDE (Eclipse, IntelliJ, etc.). Let’s call it «MyLibrary».

Step 2: Create a new package

Right-click on the «src» folder and create a new package. Let’s call it «com.mypackage».

Step 3: Create your classes

Create your classes inside the «com.mypackage» package. Let’s create a simple class called «Calculator» with two methods: «add» and «subtract».

package com.mypackage; public class Calculator  public static int add(int a, int b)  return a + b; > public static int subtract(int a, int b)  return a - b; > >

Step 4: Export your library

Now, we need to export our library as a JAR file. Right-click on the project and select «Export». Choose «Java» -> «JAR file» and click «Next».

Select the files you want to export (in our case, all files in the «src» folder) and choose the export destination. Click «Finish» to export your library.

Step 5: Use your library

To use your library in another project, simply add the JAR file to the classpath. You can do this in your IDE or by using the command line.

import com.mypackage.Calculator; public class Main  public static void main(String[] args)  System.out.println(Calculator.add(1, 2)); // Output: 3 System.out.println(Calculator.subtract(5, 3)); // Output: 2 > >

That’s it! You have successfully created a Java library using the «Package your code into a library» method.

Method 3: Create a jar file

Creating a Java library is a great way to reuse code across multiple projects. One way to create a Java library is to use a jar file. Here are the steps to create a Java library using a jar file:

1. Create a new Java project in your IDE (Eclipse, IntelliJ, etc.).
2. Write the code for your library. Make sure to include public methods that other developers can use.
3. Export your project as a jar file. In Eclipse, you can do this by right-clicking on your project, selecting «Export», and then selecting «Java > JAR file». In IntelliJ, you can do this by going to «File > Project Structure > Artifacts» and then adding a new jar artifact.
4. Make sure to select the option to include the source code and javadoc in the jar file.
5. Once you have exported your jar file, you can use it in other projects by adding it to your classpath. In Eclipse, you can do this by right-clicking on your project, selecting «Build Path > Configure Build Path», and then adding the jar file to your project’s libraries. In IntelliJ, you can do this by going to «File > Project Structure > Libraries» and then adding the jar file to your project’s dependencies.

Here is an example of a simple Java library that provides a method to calculate the factorial of a number:

package com.example.math; public class MathUtils  /** * Calculates the factorial of a number. * * @param n the number to calculate the factorial of * @return the factorial of the number */ public static int factorial(int n)  if (n == 0)  return 1; > else  return n * factorial(n - 1); > > >

To export this library as a jar file in Eclipse, you would follow these steps:

1. Right-click on the project in the Package Explorer and select «Export».
2. Select «Java > JAR file» and click «Next».
3. Select the resources to export. In this case, you would select the «com.example.math» package and its subpackages, as well as the «Export class files with compile warnings» option.
4. Choose a destination for the exported jar file and click «Finish».

Once you have exported the jar file, you can use it in another project by adding it to the classpath. Here’s an example of how to use the MathUtils library in another project:

import com.example.math.MathUtils; public class Main  public static void main(String[] args)  int result = MathUtils.factorial(5); System.out.println("Factorial of 5 is " + result); > >

In this example, we import the MathUtils class from the com.example.math package and use its factorial method to calculate the factorial of 5. The output of this program would be «Factorial of 5 is 120».

Method 4: Publish your library to a repository

This tutorial will guide you through the process of creating a Java library and publishing it to a repository. We will be using Maven as our build and dependency management tool.

Step 1: Create a new Maven project

Create a new Maven project in your preferred IDE. This can be done by selecting «New Project» and then «Maven Project». Follow the prompts to create the project.

Step 2: Define your library

Define the classes and interfaces that will make up your library. For example, let’s create a simple library that provides a utility method for generating a random number between two values.

public class RandomNumberGenerator  public static int generateRandomNumber(int min, int max)  return (int) (Math.random() * (max - min + 1) + min); > >

Step 3: Configure your Maven project

Open the pom.xml file in your project and add the following configuration:

groupId>com.examplegroupId> artifactId>my-libraryartifactId> version>1.0.0version> packaging>jarpackaging>

This configuration sets the group ID, artifact ID, version, and packaging type for your library.

Step 4: Build your library

Build your library by running the following command in your project directory:

This will compile your code, run any tests, and package your library into a JAR file.

Step 5: Publish to a repository

Publish your library to a repository by adding the following configuration to your pom.xml file:

distributionManagement> repository> id>my-repoid> url>https://myrepo.com/releasesurl> repository> distributionManagement>

Replace «my-repo» with the ID of your repository and «https://myrepo.com/releases» with the URL of your repository.

Then, run the following command to deploy your library to the repository:

Your library is now published to the repository and can be used by other projects as a dependency.

Step 6: Use your library

To use your library in another project, add the following dependency to your pom.xml file:

dependency> groupId>com.examplegroupId> artifactId>my-libraryartifactId> version>1.0.0version> dependency>

You can now use the classes and methods from your library in your project.

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