Collections使用：unmodifiableList

Collections.unmodifiableList a configuration can not be modified for the List, the following examples:

package collection;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class CollectionDemo {

    public static void main(String[] args) {
        List<String> list = new ArrayList<>();
        list.add("a");
        List<String> unmodifiableList = Collections.unmodifiableList(list);
        unmodifiableList.add("b");
    }

}

After running the effect is as follows:

Exception in thread "main" java.lang.UnsupportedOperationException
at java.util.Collections$UnmodifiableCollection.add(Unknown Source)
at collection.CollectionDemo.main(CollectionDemo.java:13)

list using the unmodifiableList package will not be modified, modify the error.