Question

This is the code I have, please look at it before you read the question

 package ict201jansem2012;


public class Qn3b {

    public static void main(String[] args) {
        int a = 1;
        int b[] = {4,5};
        String s = "Good luck!";
        method1(b[1]);
        System.out.println("(1) b[0] = "+b[0]+"; b[1] = "+b[1]);
        method2(b);
        System.out.println("(2) b[0] = "+b[0]+"; b[1] = "+b[1]);
        method3(a);
        System.out.println("(3) a = " + a );
        method4(s);
        System.out.println("(4) s = " + s );
    }
    public static void method1(int b) {
        b = 7;
    }
    public static void method2(int[] b) {
        b[0] = 3;
    }
    public static void method3(int a) {
        a = 3;
    }
    public static void method4(String s) {
        s = "UniSIM";
    }
}

Output:
(1) b[0] = 4; b[1] = 5

(2) b[0] = 3; b[1] = 5

(3) a = 1

(4) s = Good luck!

So my question is ,
This is intresting for me to know as learning programmer. The int b array 0 index value has changed, but not the other variables like the String s and int a. Before i ran this program I roughly thought in my mind that the variable will change their values as the methods are called ,this is because the method is being called and the main method vairable such as a,s and b array are passed and then they are being modified.

So in a nutshell why is that the b array 0 index is changed while the other variables are not changed?

Answer 1

Java is pass-by-value, but most values (everything that’s not a primitive, in this case int[] and String) are references, which means they act like pass-by-reference.

Here’s a nice writeup: http://javadude.com/articles/passbyvalue.htm