AVAJAVA Web Tutorials

Some confusion can be experienced by developers when they first start working with JavaSW method arguments. Are Java method arguments pass-by-reference or pass-by-value? They are pass-by-value, but this actually requires some clarification.

This tutorial will use two Java classes to demonstrate this. The Test class contains our main method:

Test.java

package test;

import java.io.IOException;

public class Test {

	public static void main(String[] args) throws IOException {

		int a = 1;
		System.out.println("a (in main) is: " + a);
		doSomething(a);
		System.out.println("a (in main) is: " + a);

		MyTest myTest = new MyTest();
		System.out.println("\nmyTest's x (in main) is: " + myTest.getX());
		doSomething(myTest);
		System.out.println("myTest's x (in main) is: " + myTest.getX());

		String s = "str1";
		System.out.println("\ns (in main) is: " + s);
		doSomething(s);
		System.out.println("s (in main) is: " + s);

		try {
			MyTest myTest2 = new MyTest();
			myTest2 = null;
			System.out.print("\nmyTest2's x (in main) is: ");
			System.out.println(myTest2.getX());
		} catch (RuntimeException e) {
			System.out.println(e);
		}

		MyTest myTest3 = new MyTest();
		System.out.println("\nmyTest3's x (in main) is: " + myTest3.getX());
		doSomethingAndNull(myTest3);
		System.out.println("myTest3's x (in main) is: " + myTest3.getX());

	}

	public static void doSomething(int a) {
		a = 2;
		System.out.println("a (in doSomething) is: " + a);
	}

	public static void doSomething(MyTest myTest) {
		myTest.setX(2);
		System.out.println("myTest's x (in doSomething) is: " + myTest.getX());
	}

	public static void doSomething(String s) {
		s = "str2";
		System.out.println("s (in doSomething) is: " + s);
	}

	public static void doSomethingAndNull(MyTest myTest3) {
		myTest3.setX(3);
		System.out.println("myTest3's x (in doSomethingAndNull) is: " + myTest3.getX());
		myTest3 = null;
	}

}

The MyTest class is a basic Java class that contains an 'x' field and getter and setter methods for that field.

MyTest.java

package test;

public class MyTest {

	int x;

	public MyTest() {
		x = 1;
	}

	public int getX() {
		return x;
	}

	public void setX(int x) {
		this.x = x;
	}
	
}

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