Question

After running the code below I get this output:
Eve
1200

Could anyone explain me why the value of Person type variable is being changed and value of Integer type variable is not?
I have already read this:

1. http://www.javaworld.com/javaworld/javaqa/2000-05/03-qa-0526-pass.html
2. http://www.yoda.arachsys.com/java/passing.html#formal

but I don’t get why with Person and Integer types it works different.

public class Test {
    public static void main(String[] args) {
        Object person = new Person("Adam");
        Object integer = new Integer("1200");

        changePerson(person);
        changeInteger(integer);

        System.out.println(person);
        System.out.println(integer);
    }

    private static void changeInteger(Object integer) {
        integer = 1000;
    }

    private static void changePerson(Object person) {
        ((Person)person).name="Eve"; 
    }
}

Answer 1

In Java, primitive types (such as integer) are always handled exclusively by value, and objects (such as your Person) and arrays are always handled exclusively by reference.

If you pass a primitive the value will be copied, if you pass a reference type the address will be copied, hence the differences.

If you follow those links above and/or do a bit of googlin’ you’ll find out more.