Modifying a Set without generating a copy of it.

Question

Hello,
My question is, how can I modify the Set I pass to a function directly instead of generating a copy of it. Here's what I mean;
This function will achieve what I want.
       public static Set<String> changeSet(Set<String> passedSet) {
        HashSet<String> changedSet = new HashSet<String>();
        for (String item : passedSet ) {
            changedSet.add(item + "<Changed>");
        return changedSet;
    }However, I have to create a secondary set called changedSet which essentially copies the passedSet with altered items.
How can I iterate through passedSet and modify its items directly? Feel free to let me know if I am on crack and don't make sense.

Answer 1

With immutable objects (e.g., instances of java.lang.String), you'll need to replace the element in the Set.
import java.util.*;
public class Foo {
    public static void main(String[] args) {
        Set<String> set = new HashSet<String>();
        set.add("foo");
        modify(set);
        assert !set.contains("foo");
        assert set.contains("foo<Changed>");
    static void modify(Set<String> set) {
        for (Iterator<String> iter = set.iterator(); iter.hasNext(); ) {
            String s = iter.next();
            set.remove(s);
            set.add(s + "<Changed>");
How can I iterate through passedSet and modify its items directly?If you're passing a set of mutable objects, then just use the foreach loop and modify the object via the reference.
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