Making a Collection Read-Only : HashSet « Collections « Java Tutorial

1. Java Tutorial
2. Collections
3. HashSet

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;

public class Main {
  public static void main(String[] argv) throws Exception {

    List stuff = Arrays.asList(new String[] { "a", "b" });

    List list = new ArrayList(stuff);
    list = Collections.unmodifiableList(list);

    try {
      list.set(0, "new value");
    } catch (UnsupportedOperationException e) {
      
    }

    Set set = new HashSet(stuff);
    set = Collections.unmodifiableSet(set);

    Map map = new HashMap();
    map = Collections.unmodifiableMap(map);
  }
}