Several methods of Map initialization in Java

# 传统方式
Map<String, String> map = new HashMap<>();
map.put("k1", "v1");
map.put("k2", "v2");

# java8新特性-双括号初始化
Map<String, String> map1 = new HashMap<>() {
    
    {
    
    
    put("k1", "v1");
    put("k2", "v2");
}};

# java9新特性-最简便的方式
Map<String, String> map2 = Map.of("k1", "v1", "k2", "v2");

# com.google.guava提供的方法
Map<String, String> map3 = ImmutableMap.of("k1","v1","k2","v2");

Reference: https://blog.csdn.net/csdn_zxh/article/details/120986368