java pass by value.

[jing hu]

I want to assign set. But now it doesn't meet my requirement.
when using set = newSet; it doesn't change.
I know the reason. I want to know if there is a convenient method assign set with newSet.
Thanks.

package pkg;

import java.util.HashSet;
import java.util.Set;

public class ValueReference {
    public static void f(Set<String> set) {
        Set<String> newSet = new HashSet<String>();
        set.add("1");
        set.add("2");
        set.add("3");
        newSet.add("one");
        newSet.add("two");
        newSet.add("three");
        set = newSet;
    }

    public static void main(String[] args) {
        Set<String> set = new HashSet<String>();
        f(set);
        System.out.println(set);
    }
}

[Christophe Verré]

If the Set you pass to the method is not null, you could call set.clear().
But you could also return a Set, instead of passing it as a parameter.

[jing hu]

yeah，I can return the newSet directly in this case.
But this is just a example. in the reality, Maybe I can't modify the function return type or there is already an returned type.
So any other method?

[Christophe Verré]

Not that I can think of. "Clear and Add" or "Create, Add and Return". That looks enough to me.

Maybe I can't modify the function return type or there is already an returned type.

Then you'd probably pass an existing Set, or encapsulate the Set in a object and pass the object to the method.

[jing hu]

ok.
I can write like this.

set.clear();
set.addAll(newSet);

what about the code efficiency ?