Java 中 Map 初始化的几种方法

港控/mmm° 2024-03-08 08:14 69阅读 0赞

**传统方式**

# 传统方式
    Map<String, String> map = new HashMap<>();
    map.put("k1", "v1");
    map.put("k2", "v2");
    
    private static final Map<String, String> myMap = new HashMap<>();
    static {
        
        myMap.put("key1", "value1");
        myMap.put("key2", "value2");
    }

**java8新特性-双括号初始化**

# java8新特性-双括号初始化
    Map<String, String> map1 = new HashMap<>() {
        {
        
        put("k1", "v1");
        put("k2", "v2");
    }};
    
    # 慎用 非静态内部类/匿名内部类包含了外围实例的引用，如果拥有比外部类更长的生命周期，有内存泄露隐患
    private static final HashMap<String, String> myMap1 = new HashMap<>() {
        {
        
        put("key1", "value1");
        put("key2", "value2");
    }};

**java9新特性-最简便的方式**

# java9新特性-最简便的方式
    Map<String, String> map2 = Map.of("k1", "v1", "k2", "v2");
    
    # 不可变集合
    private static final Map<String, String> myMap20 = Map.of(); 
    private static final Map<String, String> myMap2 = Map.of("kye1", "value1", "key2", "value2"); 
    private static final Map<String, String> myMap21 = Map.of("kye1", "value1", "key2", "value2","kye3", "value1","kye4", "value1","kye5", "value1","kye6", "value1","kye7", "value1","kye8", "value1","kye9", "value10","kye10", "value1");

**com.google.guava提供的方法**

# com.google.guava提供的方法
    Map<String, String> myMap3 = ImmutableMap.of("kye1", "value1", "key2", "value2");
    Map<String, String> myMap4 = ImmutableMap.<String, String>builder().put("kye1", "value1").put("key2", "value2").build();
    
    <dependency>
        <groupId>com.google.guava</groupId>
        <artifactId>guava</artifactId>
        <version>30.1.1-jre</version>
    </dependency>

--------------------

**参考**  
**[Java Map初始化的几种方法][Java Map]**  
**[Map用法总结][Map]**

[Java Map]: https://blog.csdn.net/csdn_zxh/article/details/120986368
[Map]: https://juejin.cn/post/7104985066605903908