Java™ How to Program, Seventh Edition

19.13. Unmodifiable Collections

The Collections API provides a set of static methods that create unmodifiable wrappers for collections. Unmodifiable wrappers throw UnsupportedOperationExceptions if attempts are made to modify the collection. Headers for these methods are listed in Fig. 19.23. Details about these methods are available at java.sun.com/javase/6/docs/api/java/util/Collections.html. All these methods take a generic type and return an unmodifiable view of the generic type. For example, the following code creates an unmodifiable List (list2) that stores String objects:

List< String > list1 = new ArrayList< String >();
List< String > list2 = Collections.unmodifiableList( list1 );

Figure 19.23. Unmodifiable wrapper methods.

public static ...