Java 中 Map 初始化的几种方法

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
Map用法总结