How To Create Custom Library

How to Create Custom Java Library

1Create Project Structure

CustomLib │ ├───bin │ └───src └───com └───mylib MathUtils.java

MathUtils.java

package com.mylib;

public class MathUtils {
    
    public static int add(int a, int b) {
        return a + b;
    }
    
    public static int subtract(int a, int b) {
        return a - b;
    }
    
    public static int multiply(int a, int b) {
        return a * b;
    }
    
    public static double divide(int a, int b) {
        return (double) a / b;
    }
}

2Compiling the Project

javac -d bin src/com/mylib/MathUtils.java

After compilation, your project structure will look like:

CustomLib │ ├───bin │ └───com │ └───mylib │ MathUtils.class └───src └───com └───mylib MathUtils.java

3Create JAR File

What is a JAR file?
JAR (Java Archive) is a collection of .class files packaged together for easy distribution and reuse.

jar -cf math.jar -C bin .

Final project structure:

CustomLib │ math.jar │ ├───bin │ └───com │ └───mylib │ MathUtils.class └───src └───com └───mylib MathUtils.java

4Using the Custom Library

Create New Project: "UseCustomLib"

UseCustomLib │ ├───bin │ ├───lib │ math.jar │ └───src └───p1 Main.java

Main.java

package p1;

import com.mylib.MathUtils;

public class Main {
    
    public static void main(String[] args) {
        
        System.out.println("Addition: " + MathUtils.add(10, 5));
        System.out.println("Subtraction: " + MathUtils.subtract(10, 5));
        System.out.println("Multiplication: " + MathUtils.multiply(10, 5));
        System.out.println("Division: " + MathUtils.divide(10, 5));
    }
}

5Compile the Project

javac -cp ./lib/math.jar -d bin src/p1/Main.java

After compilation:

UseCustomLib │ ├───bin │ └───p1 │ Main.class │ ├───lib │ math.jar │ └───src └───p1 Main.java

6Run the Program

java -cp ./bin;./lib/math.jar p1.Main

Expected Output:

Addition: 15 Subtraction: 5 Multiplication: 50 Division: 2.0