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Thread: Why am I getting the wrong sum in netbeans?

  1. #1
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    Default Why am I getting the wrong sum in netbeans?

    Netbeans is giving me the wrong sum.
    package sum;
     
    import java.util.Random;
     
    public class Sum {
     
        public static void main(String[] args) {    
            int[] x=new int[2];
            int[] y=new int[2];        
            Data data=new Data();        
            Random rand=new Random();
            int r1,r2;//Results of random numbers.
     
            r1=rand.nextInt(2);
            System.out.println("First random number is: "+r1);
            r2=rand.nextInt(2);
            System.out.println("Second random number is: "+r2);
     
            if(r1==0){
                x=data.a();
            }else if(r1==1){
                x=data.b();
            }
     
            if(r2==0){
                y=data.a();
            }else if(r2==1){
                y=data.b();
            }
     
            int result=x[0]+y[0];
     
            System.out.println("The sum is: "+result);
            //I get the wrong sum when I get '1' and '0'.
        }
    }
    This is a the java class of the data.
    package sum;
     
    public class Data {
        int[] x=new int[2];
        public int[] a(){
            x[0]=300;
            x[1]=3;
            return x;   
        }
        public int[] b(){
            x[0]=250;
            x[1]=2;
            return x;
        }
    }

    This all the codes.
    I donīt know why it is giving me the wrong answer. Thanks in advance.
    Last edited by jms; April 24th, 2019 at 12:03 PM.

  2. #2
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    Default Re: Why am I getting the wrong sum in netbeans?

    Please repost your code and include the classes. What you posted are just parts of the code.

    Regards,
    Jim

  3. #3
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    Default Re: Why am I getting the wrong sum in netbeans?

    Hi, I have reposted all the codes. It is a small test program for learning. Regards.

  4. #4
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    Default Re: Why am I getting the wrong sum in netbeans?

    The problem is that you are passing back a reference to an array from your Data class. So let's say you first assign the array to x. Then when you call the method again, you are changing the array to another value which also affects the value x has. To solve this problem, make the array local to both Data.a and Data.b.

    Regards,
    Jim

    --- Update ---

    Here is a simpler example to explain the problem.

    public class SimpleExample {
     
       public static void main(String[] args) {
    	  MyData data = new MyData();
    	  int[] x = data.a(); // x[0] = 200
    	  int[] y = data.b(); // x[0] and y[0] both = 900;
                                         // this is because the call to data.b() also changed the array  that
                                         // x has a reference to.  x and y share the same array.
    	  System.out.println(x[0] + y[0]);
       }
     
    }
     
    class MyData {
       int array[] = new int[1];
     
       public int[] a() {
    	  array[0] = 200;
    	  return array;
       }
     
       public int[] b() {
    	  array[0] = 900;
    	  return array;
       }
    }

  5. The Following User Says Thank You to jim829 For This Useful Post:

    jms (April 24th, 2019)

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    Default Re: Why am I getting the wrong sum in netbeans?

    Thank you very much!!!

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