is java support call by reference and call by value, if
supports please explain?

Answer Posted / sreevani

Java doesn't pass method arguments by reference; it passes
them by value.


Take the badSwap() method for example:

public void badSwap(int var1, int var2)
{
int temp = var1;
var1 = var2;
var2 = temp;
}


When badSwap() returns, the variables passed as arguments
will still hold their original values. The method will also
fail if we change the arguments type from int to Object,
since Java passes object references by value as well.
Now, here is where it gets tricky:

public void tricky(Point arg1, Point arg2)
{
arg1.x = 100;
arg1.y = 100;

Point temp = arg1;
arg1 = arg2;
arg2 = temp;
}

public static void main(String [] args)
{
Point pnt1 = new Point(0,0);
Point pnt2 = new Point(0,0);
System.out.println("X: " + pnt1.x + " Y: " +pnt1.y);
System.out.println("X: " + pnt2.x + " Y: " +pnt2.y);
System.out.println(" ");
tricky(pnt1,pnt2);
System.out.println("X: " + pnt1.x + " Y:" + pnt1.y);
System.out.println("X: " + pnt2.x + " Y: " +pnt2.y);
}

If we execute this main() method, we see the following
output:

X: 0 Y: 0
X: 0 Y: 0

X: 100 Y: 100
X: 0 Y: 0

The method successfully alters the value of pnt1, even
though it is passed by value; however, a swap of pnt1 and
pnt2 fails! This is the major source of confusion. In the
main() method, pnt1 and pnt2 are nothing more than object
references. When you pass pnt1 and pnt2 to the tricky()
method, Java passes the references by value just like any
other parameter. This means the references passed to the
method are actually copies of the original references.

Java copies and passes the reference by value, not the
object. Thus, method manipulation will alter the objects,
since the references point to the original objects. But
since the references are copies, swaps will fail. As Figure
2 illustrates, the method references swap, but not the
original references. Unfortunately, after a method call,
you are left with only the unswapped original references.
For a swap to succeed outside of the method call, we need
to swap the original references, not the copies.

Is This Answer Correct ?    26 Yes 9 No



Post New Answer       View All Answers


Please Help Members By Posting Answers For Below Questions

Can I extend singleton class in java?

845


How can we make sure main() is the last thread to finish in java program?

937


If we don’t want some of the fields not to serialize how to do that?

788


How to perform binary search in java?

782


Why is it called a string?

749


Explain the scope of a variable.

845


What are the differences between include directive and include action?

768


What happens if an exception is throws from an object's destructor?

799


What is the base class of all exception classes?

814


What is == and === in javascript?

771


What is callablestatement? How you can call stored procedure to pass in parameter?

761


Explain a few methods of overloading best practices in java?

744


Is array synchronized in java?

800


take an array with -ve and +ve value both.find out the nearest value of 0(zero).if two values are same like(-2 and +2)then extract +2 is nearest of 0(zero).

1761


What do you mean by chromounits in java8?

718