Java Collections emptyList() 方法和示例

Java Collections 的emptyList()方法返回没有元素的列表。这种方法是不可变的。也就是说，我们在创建这个方法后不能做任何修改。

句法：

public static final  List emptyList()

参数：它不会接受任何参数

返回：此方法将返回一个空列表

示例 1：

Java

// Java program to create an empty list
import java.util.*;
 
public class GFG {
 
    public static void main(String[] args)
    {
        // create a list that is empty
        List mylist
            = Collections.emptyList();
             
        // display the list
        System.out.println(mylist);
    }
}

Java

// Java program to show an exception
// when adding the elements to the list
import java.util.*;
 
public class GFG {
 
    public static void main(String[] args)
    {
        // create a list that is empty
        List mylist
            = Collections.emptyList();
 
        // add 5 elements to the created list
        mylist.add(1);
        mylist.add(2);
        mylist.add(3);
        mylist.add(4);
        mylist.add(5);
 
        // display the list
        System.out.println(mylist);
    }
}

输出

[]

示例 2：

Java

// Java program to show an exception
// when adding the elements to the list
import java.util.*;
 
public class GFG {
 
    public static void main(String[] args)
    {
        // create a list that is empty
        List mylist
            = Collections.emptyList();
 
        // add 5 elements to the created list
        mylist.add(1);
        mylist.add(2);
        mylist.add(3);
        mylist.add(4);
        mylist.add(5);
 
        // display the list
        System.out.println(mylist);
    }
}

输出：

Exception in thread "main" java.lang.UnsupportedOperationException
    at java.util.AbstractList.add(AbstractList.java:148)
    at java.util.AbstractList.add(AbstractList.java:108)
    at GFG.main(GFG.java:11)