Q: why the swap func didnt work for me? 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


A: 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.

A: 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.
