Why is my output different after each execution of the program?

Question

So I am new to java and was trying to learn about simple data structure and wrote a program in bluej to pop in a stack. However after compiling and executing the program the output is different each time.

The code is as follows:

class popstack
{
    static int arr[]={31,45,64,100};

   public static void main()
    {
     int top=0;
     int i=top;
     System.out.println(arr[top]);
     while(i<3){
         arr[i]=arr[i+1];
         arr[i+1]=0;
         i=i+1;
         
     }
     
      for(int j=0;j<4;j++)
        {
            System.out.print(arr[j]+",");
        }
    }
}

Expected Output: 1st execution :

31
45,64,100,0,

2nd execution :

31
45,64,100,0,

Output: 1st execution :

31
45,64,100,0,

2nd execution :

45
64,100,0,0,

Shouldn't the outputs be same since i am always initializing the array?

EDIT: The issue was fixed when i added the paramter string[] args to the main method.

This works fine running it in Eclipse. Possibly something to do with the way you are running it in BlueJ. — greg-449
– greg-449, Commented Mar 17 at 14:23

aled · Accepted Answer · 2025-03-17 14:33:19Z

1

For some reason your IDE is not starting a new execution the second time but calling the main() method again while still in the previously executing JVM. Since each execution modifies the values of the array arr you are seeing the second time the values modified from the first execution.

If the JVM finished a new execution would create a fresh JVM process and the values in memory would be carried over from the old one. That is the expected result when executing from the command line for example.

answered Mar 17 at 14:33

aled

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2 Comments

Federico klez Culloca Mar 17 at 15:26

"For some reason" I suppose it has something to do with the main method being defined without parameters.

Darky Mar 17 at 15:33

Oh ok. I added the string [ ] args parameter and now it works. thanks

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