why the swap func didnt work for me?

Question

i start learn java, and i build 'swap' function that replaces numbers.

when i run this code, its not replace them.

how could i solve this problem?

public static void swap(double i, double j){
        double temp = i;
        i = j;
        j = temp;
}

this in the main:

double i = 1;
double j = 2;
System.out.println(i+" - "+ j);
swap(i, j);
System.out.println(i+" - "+ j);

in the Console i see:

1.0 - 2.0
1.0 - 2.0

and i need to see:

1.0 - 2.0
2.0 - 1.0

@SotiriosDelimanolis: That statement means nothing to a Java neophyte. — Robert Harvey, Sep 17 '13 at 16:03
@RobertHarvey Sure, but it's a keyword that they can look up. — Sotirios Delimanolis, Sep 17 '13 at 16:04

score 1 · Accepted Answer · answered Sep 17 '13 at 16:03

In Java, everything is passed by value, including primitive types. You have copies of i and j in your swap method. You did swap the values i and j, but only the local values i and j in the scope of your swap method. The i and j in main were not changed.

To swap the values, implement the swap code inline in the main method, not in a separate method.

score 1 · Answer 2 · answered Sep 17 '13 at 16:03

1

Java is pass by value, even for references. You are changing a copy of the original values, not the originals.

There is no way to implement a swap method in Java to do what you suggest.

answered Sep 17 '13 at 16:03

Peter Lawrey

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why the swap func didnt work for me?

2 Answers2