immutable class from mutable objects

ThreeStooges.java

public final class ThreeStooges {
    private final Set<String> stooges = new HashSet<String>();
        
    public ThreeStooges() {
        stooges.add("Moe");
        stooges.add("Larry");
        stooges.add("Curly");
    }
    
    public boolean isStooge(String name) {
        return stooges.contains(name);    
    }
}