java is pass by value????

[suavedeep kaur]

i am confused about the java's concept of pass by value ............as some books say java is all pass by value


and some says Primitive types are passed by value and
Objects are passed by reference


please can someone explain in detail whats the reson n how it happens???

[Michael Dunn]

simple demo, if it was pass-by-ref, 'list' would change

    
import java.util.*;
class Testing
{
  List<String> list;
  public Testing()
  {
    list = new ArrayList<String>(Arrays.asList(new String[]{"a","b","c"}));
    System.out.println("Contents of 'list':");
    printList(list);
    testPassByValue(list);
  }
  public void printList(List listToBePrinted)
  {
    for(int x = 0, y = listToBePrinted.size(); x < y; x++) System.out.println(listToBePrinted.get(x));
    System.out.println("===");
  }
  public void testPassByValue(List passByValueList)
  {
    System.out.println("Contents of 'passByValueList':");
    printList(passByValueList);
    passByValueList = new ArrayList<String>(Arrays.asList(new String[]{"x","y","z"}));
    System.out.println("Contents of changed 'passByValueList':");
    printList(passByValueList);
    System.out.println("Contents of 'list', called from 'testPassByValue':");
    printList(list);
  }
  public static void main(String[] args){new Testing();}
}

[Jesper de Jong]

Welcome to JavaRanch.

Yes, Java is pass by value only. But the confusing thing is that references are also passed by value.

For more information, see this JavaRanch Campfire Story: Pass-by-Value Please

[Amit Ghorpade]

Hi suavedeep kaur welcome to Javaranch,

i am confused about the java's concept of pass by value ............as some books say java is all pass by value


and some says Primitive types are passed by value and
Objects are passed by reference

In which book did you find that Objects are passed by reference
It's actually object references are passed by value and not objects.

Hope this helps

[Amit Ghorpade]

And yes

as some books say java is all pass by value

Why only some books all books say so.

Hope this helps

[suavedeep kaur]

sir f have complete reference its on page 133

i am new to java so exploring it

its what all is written
objects are passed by value

[suavedeep kaur]

//  object refrences are  also passed by value
 
class Test{
 int a,b;
 
 
 Test (int i ,int j ) {
 a=i ;
 b=j ;
 
 }
 
 // pass an object
 
 void meth(Test o ){
 o.a *=2 ;
 o.b /= 2;
   }
 }
 
 
class  CallByRef {
public static void main (String args[]) {
Test ob = new Test(15,20);
 
System.out.println(" ob.a and ob.b before call : " + ob.a + " " + ob.b);
 
ob.meth(ob);
 
System.out.println("ob.a and ob.b  after  call : " + ob.a + " " + ob.b);
  }
}

[edit]Add code tags. CR[/edit]
[ July 21, 2008: Message edited by: Campbell Ritchie ]

[suavedeep kaur]

Thanks sir i got my doubt cleared

[Campbell Ritchie]

Originally posted by suavedeep kaur:
Thanks sir i got my doubt cleared

Well done. This is a common problem, and causes quite a lot of confusion, particularly when some books are not precise in how they describe it.
Click the search button above, and put "pass by value" in the box. You get lots of links; try this one, and look at the "wonderful link" quoted in the 3rd message. It is a bit complicated, but explains very clearly what pass-by-reference would be and how in works in Pascal. You can then try it out in Java, as in Michael Dunn's example, and you can see how the results are different.