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To create a read-only list, use the unmodifiableList() method of the Collections class

import java.util.ArrayList; import java.util.Collections; import java.util.List; public class MainClass {   public static void main(String args[]) throws Exception {     List list = new ArrayList();     list.add("A");     list.add("B");     list.add("C");     list = Collections.unmodifiableList(list);     list.add(1, "G");     System.out.println(list);   } } Exception in thread "main" java.lang.UnsupportedOperationException at java.util.Collections$UnmodifiableList.add(Collections.java:1160) at MainClass.main(MainClass.java:14)