java pass by value

[thejwal pavithran]

Hey guys,

I am having difficulty understanding How parameters are passed in java.

heres my code:

Hippo.java
public class Hippo
{
	int size;
	public void dance()
	{
		System.out.println("I am a Hippo and I am dancing");
	}
}

TestHippo.java
class TestHippo
{
	public static void main(String[] args)
	{
		Hippo h1=new Hippo();
		Hippo h2=h1;
		h1.size=100;
		System.out.println("h1.size="+h1.size);
		System.out.println("h2.size="+h2.size);
		h2.dance();
		String s1=null;
		System.out.println(s1);
		copy(h2,s1);
		System.out.println("h1.size="+h1.size);
		System.out.println("h2.size="+h2.size);
		System.out.println(s1);

	}

	static void copy(Hippo copyHippo,String s2)
	{
		System.out.println("copyHippo.size="+copyHippo.size);
		copyHippo.size=200;
		s2="hi";

	}
}

so i am passing the address of Hippo h2 to copyHippo through method copy. So when i modify the value of size of copyHippo in the copy method, it gets reflected in the main method, which can be seen by the output of the sop.

I just cant understand why the string variables value is not getting modified. Because isnt it completely similar to the copyHippo reference variable?

but why is the value of s2(null here)passed instead of the address.
I mean copyHippo is a reference variable which points to the same object to which h2 and h1 created in the main method are pointing to.so when i modify the value of instance variables of copyHippo in the copy function, the values of instance variables in the main function gets modified.

Same should be the case for the string variable too right? But what am i missing here?

I need to understand this.please help

[jatan bhavsar]

Hi ,

Refer this . It will solve your doubts.

Regards
jatan

[James Boswell]

This question is more related to the behaviour of Strings as opposed to passing by value. See here about Strings: http://docs.oracle.com/javase/tutorial/java/data/strings.html. The important fact is that Strings are immutable.

[Stuart A. Burkett]

James Boswell wrote:This question is more related to the behaviour of Strings as opposed to passing by value. See here about Strings: http://docs.oracle.com/javase/tutorial/java/data/strings.html. The important fact is that Strings are immutable.

Not really. The OP would have got the same result if s1 and s2 had been references to a mutable object.

[Stuart A. Burkett]

Deleted - meant to edit previous post rather than quote it.