How to create a read-only list in Java?

Let us first create a List in Java −

List<String>list = new ArrayList<String>(); list.add("A"); list.add("B"); list.add("C");

Now to convert the above list to read-only, use Collections −

list = Collections.unmodifiableList(list);

We have converted the above list to read-only. Now, if you will try to add more elements to the list, then the following error would be visible −

Exception in thread "main" java.lang.Error: Unresolved compilation problem:

Example

 Live Demo

import java.util.ArrayList; import java.util.Collections; import java.util.List; public class Demo {    public static void main(String args[]) throws Exception {       List<String>list = new ArrayList<String>();       list.add("A");       list.add("B");       list.add("C");       list = Collections.unmodifiableList(list);       // An exception is thrown since its a read-only list now       list.add("D");       list.add("E");       list.add("F");       System.out.println(list);    } }

The output is as follows. Since it’s a read-only list, an error would be visible −

Output

Exception in thread "main" java.lang.Error:Unresolved compilation problem: String literal is not properly closed by a double-quote at Amit/my.Demo.main(Demo.java:18)