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How to make a collection read-only in Java
Problem Description
How to make a collection read-only?
Solution
Following example shows how to make a collection read-only by using Collections.unmodifiableList() method of Collection class.
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("Collection is read-only now."); } }
Result
The above code sample will produce the following result.
Collection is read-only now.
java_collections.htm
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