How to call a method and pass parameter in java?

Question

The code is listed below. So I expected the output to be {2 4 6 8 10}, however, when I test it, the result is {1 2 3 4 5}. I am confused now, can anyone tell me why? Thanks!

public class practice{ 
    public void doubler(int[] a)
    {
        int[] b = new int[a.length];
        for(int i = 0; i< a.length; i++)
        {
            b[i] = 2*a[i];
        }
        a = b;
    }
    public static void main(String[] args) 
    {
    int[]c = {1,2,3,4,5};
        Practice w = new Practice();
        w.doubler(c);
        for(int count = 0; count<c.length; count++)
        {
            System.out.print(c[count] + " ");
        }
  }
}

How is it even allowing you to do `int[] s = w.doubler(c);` ..... is my question — 3kings, May 03 '17 at 04:00
`a` in `doubler` is a different variable from `c` in `main`. — user253751, May 03 '17 at 04:20
You will be surprised, but it is duplicate of [Is Java "pass-by-reference" or "pass-by-value"?](http://stackoverflow.com/questions/40480/is-java-pass-by-reference-or-pass-by-value) — Iłya Bursov, May 03 '17 at 04:24

score 0 · Answer 1 · answered May 03 '17 at 04:01

Since double is void method following doesnt work

int[] s=w.doubler(c);

because it would be similar as

int[] s= void; // wrong

change the return type of the method

public int[] doubler(int[] a)

and return the array b as soon as the method is done with the job

score 0 · Accepted Answer · answered May 03 '17 at 04:03

0

I think this is helpful for you,

public class practice{ 
    public int[] doubler(int[] a)
    {
        int[] b = new int[a.length];
        for(int i = 0; i< a.length; i++)
        {
            b[i] = 2*a[i];
        }
        return b;
    }
    public static void main(String[] args) 
    {
    int[]c = {1,2,3,4,5};
        Practice w = new Practice();
        int[] s=w.doubler(c);
        for(int count = 0; count<s.length; count++)
        {
            System.out.print(s[count] + " ");
        }
    } 
}

I your case, you didn't return multiplied array to int[] s.

answered May 03 '17 at 04:03

Kushan

10,657
4
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I did it but it still gives me the same output...(1 2 3 4 5) – Cheryl Liang May 03 '17 at 04:08
Did you loop output for int[] s like this , System.out.print(s[count] + " "); – Kushan May 03 '17 at 04:11
1

@CherylLiang literally copy and paste his code and it works. – Nick Ziebert May 03 '17 at 04:12

score 0 · Answer 3 · answered May 03 '17 at 04:04

0

Change method doubler to :

public int[] doubler(int[] a)
    {
        int[] b = new int[a.length];
        for(int i = 0; i< a.length; i++)
        {
            b[i] = 2*a[i];
        }
        return b;
    }

This will give you new array b.

answered May 03 '17 at 04:04

Jay Smith

2,331
3
16
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Thanks for replying. I did it but it still prints out the original c array. I feel like there is something wrong with my main method. – Cheryl Liang May 03 '17 at 04:17
You have to do `c = w.doubler(c);` in main method. – Jay Smith May 03 '17 at 04:19

How to call a method and pass parameter in java?

3 Answers3