How we can get Boolean value updated through other method in main method

Question

Please ignore formatting and sentence related issues.

class ABC 
{   
 public void change(Boolean x, Boolean y, StringBuffer s)
 {
    x=true;
    y=true;
    s.append("vinay");
 }

 public static void main(String a[])
 {
    Boolean x = false;
    Boolean y = false;
    x=false;
    y=false;
    StringBuffer s = new StringBuffer();
    s.append("jasi");
    ABC p= new ABC();
    p.change(x,y,s);

    System.out.println(x);
    System.out.println(y);
    System.out.println(s);      
 }
}

i want to get all changes which i made in change() method in main() method for Boolean x,y as we are getting s modified in main function. Is there any way by which we can get modified value in main method.

You won't even be able to see changes in a single-threaded program, because of pass-by-value. — awksp, Jun 17 '14 at 19:38
it's ok but why we are getting updated value in case of StringBuffer object s. Please clarify me it. — Vinay Sharma, Jun 17 '14 at 19:54

score 6 · Accepted Answer · answered Jun 17 '14 at 19:41

6

Java passes arguments by value, so all changes done in your change() method are not visible for caller.

In order to do what you want you can either: 1. define this variable as class members. 2. return them as a return value of the method. Yes, you are limited by only one return value but if your want to can create array of booleans or create specal class that contains both. 3. You can pass to method mutable container that contains boolean. One of the ways is to use AtomicBoolean for this:

public void change(AtomicBoolean x, AtomicBoolean y, StringBuffer s) {
    x.set(true);
    y.set(true);
    s.append("vinay");
}

public static void main(String a[]) {
    AtomicBoolean x = new AtomicBoolean(false);
    Boolean y =  = new AtomicBoolean(false);
    change(x, y);
    System.out.println(x.get() + ", " + y.get()); // will print true true
}

answered Jun 17 '14 at 19:41

AlexR

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sir but we are getting updated value in case of StringBuffer object s ? – Vinay Sharma Jun 17 '14 at 19:45
That's because a StringBuffer object can be modified. With the reference, you can change it. But the StringBuffer reference parameter is pass-by-value. That means if you make s point to a different object, it will still point to the original object outside the change() function. – Edwin Torres Jun 17 '14 at 19:52
what do you mean by mutable container that contains boolean – Vinay Sharma Jun 17 '14 at 20:01

score 1 · Answer 2 · edited May 23 '17 at 12:21

1

Options:

Place the variables outside of the two methods (as class variables)
Create an array (there for referencing an address instead of a value).
Create a new Object that contains these two Boolean values (create a new class or use an ArrayList/HashMap/etc)
AtomicBoolean

Option 1:

class ABC 
{   
    Boolean x = false;
    Boolean y = false;
    public void change(StringBuffer s)
    {
        //code
    }

     public static void main(String a[])
     {
         //code
         p.change(s);
         //code 
     }
}

Option 2:

class ABC 
{   
    public void change(Boolean b, StringBuffer s)
    {
         b[0] = true;
         b[1] = true;
        //code
    }

     public static void main(String a[])
     {
         Boolean[] b = new Boolean[2];
         b[0] = false;
         b[1] = false;
         //code
         p.change(b, s);
         //code 
     }
}

edited May 23 '17 at 12:21

Community

1
1

answered Jun 17 '14 at 19:38

But I'm Not A Wrapper Class

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Might want `volatile` too? – awksp Jun 17 '14 at 19:39
Flip the bracket. Add `;`. – PM 77-1 Jun 17 '14 at 19:39
@user3580294 Adding `volatile` or `static` would depend on OP's requirements. It doesn't necessary have to be the case, but I'll mention it. – But I'm Not A Wrapper Class Jun 17 '14 at 19:42
Oops, for some reason I read the title as "...updated through other *thread* in main method". Disregard what I said; `volatile` is not necessary here, since threading isn't involved. Apparently I need new glasses. – awksp Jun 17 '14 at 19:43
actually there are some restrictions we can not have these variables as class level. in my requirement. – Vinay Sharma Jun 17 '14 at 19:48

score 0 · Answer 3 · answered Jun 17 '14 at 19:38

0

Java is pass-by-value so when you pass the boolean here p.change(x,y,s); it will treat as pass by value and when you initialized the boolean from the change method

x=true;
y=true;

it wont grab that reference but will get destroyed when it is out of scope

answered Jun 17 '14 at 19:38

Rod_Algonquin

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sir but we are passing object to change method as we are passing s – Vinay Sharma Jun 17 '14 at 19:40
@VinaySharma put all the boolean as a global variable – Rod_Algonquin Jun 17 '14 at 19:41

score 0 · Answer 4 · answered Jun 17 '14 at 19:40

0

You can transform your boolean as static var, you'll call them with ABC.x and define just after the class with public static boolean x; It'll looks like

class ABC 
{
    public static boolean x;

answered Jun 17 '14 at 19:40

score 0 · Answer 5 · answered Jun 17 '14 at 19:40

In Java the arguments are passed by value, not as pointers, so the variables that you passed to the function have their values copied to local variables in the method, so all the changes only affects that local copy.

what you can do is get global variables, or get a return to your function.

att.

How we can get Boolean value updated through other method in main method

5 Answers5