创建一个不可修改的Set

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

public class CreateUnmodifiableSet {

public static void main(String[] args) {
    // TODO Auto-generated method stub
    System.out.println(set());
}
public static <T> Set<T> set(final T... elements) {
    final HashSet<T> set = new HashSet<T>(elements.length);
    Collections.addAll(set, elements);
    return Collections.unmodifiableSet(set);
}

public static <T> Set<T> set() {
    return new HashSet<T>();
}

/**
 * @return an <b>UNMODIFIABLE</b> Set&lt;T&gt;
 */
public static <T> Set<T> unmodifiableSet(final Set<? extends T> s) {
    return (s == null) ? Collections.<T> emptySet() : Collections
            .unmodifiableSet(s);
}

}
Console:
[]