Java教程

Java Collections emptyMap()

Java Collections 类的 emptyMap()方法返回一个不变的空映射。

语法

以下是 emptyMap()方法的声明:
public static final <K,V> Map<K,V> emptyMap() 

参数

此方法不接受任何参数。

返回

空映射()方法返回一个空的不变Map。

异常

NA

兼容版本

Java 1.5及更高版本

示例1

import java.util.*;
public class CollectionsEmptyMapExample1 {
    public static void main(String[] args) {      
         //Create an empty Map    
         Map<String,String> EmptyMap = Collections.emptyMap</span>();
         System.out.println("Created Empty Map: "+EmptyMap);
         }    
}
输出:
Created Empty Map: {}

示例2

import java.util.*;
public class CollectionsEmptyMapExample2 {
    public static void main(String[] args) {      
         //Create an empty Map   
         Map<String,String> EmptyMap = Collections.emptyMap</span>();
         System.out.println("Created Empty Map: "+EmptyMap);
         // try to add elements
         EmptyMap.put("1","from lidihuo.com");
         }    
}
输出:
Created Empty Map: {}
Exception in thread "main" java.lang.UnsupportedOperationException
    at java.base/java.util.AbstractMap.put(AbstractMap.java:209)
    at myPackage.CollectionsEmptyMapExample2.main(CollectionsEmptyMapExample2.java:9)

示例3

import java.util.*;
public class CollectionsEmptyMapExample3 {
    public static void main(String[] args) {      
        //Create an empty Map    
          Map<Integer, Integer> empMap = Collections.emptyMap</span>();
          empMap.put(1, 23424);
          empMap.put(2, 65776);    
          System.out.println("Created empty immutable Map: "+empMap);         
          }   
}
输出:
Exception in thread "main" java.lang.UnsupportedOperationException
    at java.base/java.util.AbstractMap.put(AbstractMap.java:209)
    at myPackage.CollectionsEmptyMapExample3.main(CollectionsEmptyMapExample3.java:7)

昵称: 邮箱:
Copyright © 2022 立地货 All Rights Reserved.
备案号:京ICP备14037608号-4