What is the error in the program???

[kdiswired]

I cannot understand the error in the below program. Need some help here.

class callvalue
{
	public static void main(String a[])
	{
		int x=50;
		int y=70;
		callvalue cv=new callvalue();
		cv.interchange(x,y); 
		System.out.println(x,y);
	}

	void interchange(int x1, int y1)
	{
		int z1;
		z1=x1;
		x1=y1;
		y1=z1;
		System.out.println(x1,y1);	
	}
}

[JosAH]

You haven't read the Java tutorials covering the basics, have you?

kind regards,

Jos

[pbrockway2]

Hi kdiswired, welcome to the forums!

When you post code it's a good idea to use the "code" tags. Put [code] at the start of the code and [/code] at the end - that way the code will be readable when it appears here.

I cannot understand the error in the below program.

What error?

Specifically, does the code compile? If not and you can't understand the compiler's messages, post them and someone is sure to be able to explain what they mean.

Or does the code not do at runtime what you expect or intend? In that case say what you expected and what happened. If there is a runtime exception copy and post the error message exactly as you see it.

[kdiswired]

ooops!!!! sorry.....didn't know how to use code tags.

However, the code does not compile and the error I am getting is:

callvalue.java:10:cannot find symbol
symbol:method println(int,int)
location:class java.io.PrintStream
System.out.println(x,y);
^

callvalue.java:19:cannot find symbol
symbol:method println(int,int)
location:class java.io.Printstream
System.out.println(x1,y1);
^

[DarrylBurke]

That's right. you're passing two int parameters to a method that doesn't have an overload that accepts two int parameters.

db

[pbrockway2]

ooops!!!! sorry.....didn't know how to use code tags.

That's OK! I'm applying a sort of sliding scale to these things: I'm happy to add them to a first post, I'll start directing people to the site faqs after that (becoming increasingly less polite), and then, after some number of posts, I'll just not respond to what I find hard to read.

-----

you're passing two int parameters to a method that doesn't have an overload that accepts two int parameters

I agree.

passing, parameters, overload, accept. There's so much (absolutely unavoidable) jargon here. If it's not clear your first port of call is your notes and textbooks etc. After that, say what you've looked at and what examples of println() you've found and ask db what he's getting at.

[kdiswired]

Actually....I am trying to check the call by value in java with the help of this program.....can u pls tell me whr am wrong????
How do I make the program error free???

[pbrockway2]

can u pls tell me whr am wrong?

I take it that's a frustrated attempt at "Can you please tell me where I am wrong?". Please take the time to spell words out: there are many here coping with the many oddities of English and they don't need cryptic abbreviations as an additional burden. Further, a professional manner will encourage people to respond. (Their logic is something along the lines of "you should be as serious as my time is valuable".)

You have been told what's wrong. "System.out.println(x,y)" makes no sense. The compiler is saying that there is simply no such method: no println() method that takes two int arguments like that.

If you want to print two ints, do it in two statements. Or think of some way of combining them into a single string.

[kdiswired]

Of course, I completely get it now. I was able to compile the code successfully and run it. Thank you very much. I have mentioned the correct code below.

import java.lang.*;
class callvalue
{
	public static void main(String a[])
	{
		int x=50;
		int y=70;
		callvalue cv=new callvalue();
		cv.interchange(x,y); 
		System.out.println("Calling value of x: "+x);
		System.out.println("Calling value of y: "+y);
	}

	void interchange(int x1, int y1)
	{
		int z1;
		z1=x1;
		x1=y1;
		y1=z1;
		System.out.println("Called value of x: "+x1);
		System.out.println("Called value of y: "+y1);	
	}
}

[kdiswired]

The above code gives an example of Call by Value in java. However, I do not understand the concept of Call by Reference. Need some help here.

[JosAH]

The above code gives an example of Call by Value in java. However, I do not understand the concept of Call by Reference. Need some help here.

Java doesn't implement the call by reference mechanism so there's no need to try to use it; it can't be done.

kind regards,

Jos

[pbrockway2]

I was able to compile the code successfully and run it. Thank you very much.

You're welcome - and well done!

The above code gives an example of Call by Value in java. However, I do not understand the concept of Call by Reference.

The example you constructed is a very good example of call by value. What we see is:

Called value of x: 70
Called value of y: 50
Calling value of x: 50
Calling value of y: 70

In particular the values of the argument variables get swapped within the method, but the values of the variables used as arguments do not change as a result of the method call. For me this is "call by value" semantics. No variable declared in the caller's context (x, y or anything else declared there) is going to change its value as a result of the method call interchange(x,y).

But what about so-called "reference values"? After all they have "reference" in their name! It's easy to check using your code:

import java.awt.Point;
class callvalue
{
    public static void main(String a[])
    {
        Point x = new Point(0, 50);
        Point y = new Point(0, 70);
        callvalue cv=new callvalue();
        cv.interchange(x,y); 
        System.out.println("Calling value of x: "+x);
        System.out.println("Calling value of y: "+y);
    }
 
    void interchange(Point x1, Point y1)
    {
        Point z1;
        z1=x1;
        x1=y1;
        y1=z1;
        System.out.println("Called value of x: "+x1);
        System.out.println("Called value of y: "+y1);   
    }
}

We see the same thing:

Called value of x: java.awt.Point[x=0,y=70]
Called value of y: java.awt.Point[x=0,y=50]
Calling value of x: java.awt.Point[x=0,y=50]
Calling value of y: java.awt.Point[x=0,y=70]

Values of variables within the method are swapped, but no change to the variables declared outside the method occurs.

A consequence of this pass by value semantics is that although methods can change all sorts of things, the only way a variable can change its value is through something being assigned to it somewhere within its scope: either straight forwardly or via the increment/decrement operators.

-----

The following from JavaRanch are worth reading: Cup Size -- a story about variables and Pass-by-Value Please (Cup Size continued).