Java Example - Read-Only Collection

The following example demonstrates how to use the Collections.unmodifiableList() method of the Collection class to set the collection to read-only:

/*
 author by w3cschool.cc
 Main.java
 */

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);
      System.out.println("集合现在是只读");
   }
}

The output result of running the above code is:

集合现在是只读

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