Java 如何让ArrayList只读

给定一个数组列表，任务是在Java中使这个数组列表成为只读。

例子

输入: ArrayList: [1, 2, 3, 4, 5]
输出: Read-only ArrayList: [1, 2, 3, 4, 5]

输入: ArrayList: [geeks, for, geeks]
输出: Read-only ArrayList: [geeks, for, geeks]

建议：请先在{IDE} 上尝试你的方法，然后再继续解决

在Collections.unmodifiableList()方法的帮助下，一个ArrayList可以很容易地变成只读。该方法将可修改的ArrayList作为参数，并返回该ArrayList的只读不可修改的视图。

语法。

readOnlyArrayList = Collections.unmodifiableList(ArrayList);

下面是上述方法的实现。

// Java program to demonstrate
// unmodifiableList() method
  
import java.util.*;
  
public class GFG1 {
    public static void main(String[] argv)
        throws Exception
    {
        try {
  
            // creating object of ArrayList<Character>
            List<Character> list = new ArrayList<Character>();
  
            // populate the list
            list.add('X');
            list.add('Y');
            list.add('Z');
  
            // printing the list
            System.out.println("Initial list: "
                               + list);
  
            // getting readonly list
            // using unmodifiableList() method
            List<Character>
                immutablelist = Collections
                                    .unmodifiableList(list);
  
            // printing the list
            System.out.println("ReadOnly ArrayList: "
                               + immutablelist);
  
            // Adding element to new Collection
            System.out.println("\nTrying to modify"
                               + " the ReadOnly ArrayList.");
            immutablelist.add('A');
        }
  
        catch (UnsupportedOperationException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}

输出:

Initial list: [X, Y, Z]
ReadOnly ArrayList: [X, Y, Z]

Trying to modify the ReadOnly ArrayList.
Exception thrown : java.lang.UnsupportedOperationException