import java.util.HashMap;import java.util.Map;public class BasicHashMap {    public static void main(String[] args) {        // 新建map        Map
     
       fstMap =  new HashMap<>();        // 存值        fstMap.put("a", 1);        fstMap.put("b", 2);        fstMap.put("c", 3);        fstMap.put("d", 4);        System.out.println("=== fstMap 输出 ===");        System.out.println(fstMap);        Map
      
        sndMap = new HashMap<>();        sndMap.put("ab", 1);        sndMap.put("cd", 2);        System.out.println("=== aMap.putAll(bMap) ===");        sndMap.putAll(fstMap);        System.out.println("合并后的sndMap");        System.out.println(sndMap);        System.out.println("合并后的fstMap剩余");        System.out.println(fstMap);        System.out.println("=== map.getOrDefault(aKey, dV), 有akey则返回相应的值，否则返回dV ===");        System.out.println(sndMap.getOrDefault("ab", 3));        System.out.println(sndMap.getOrDefault("m", 3));        System.out.println(sndMap);        System.out.println("=== map.put(aKey) 重复key===");        System.out.println("map put重复值，会先做get，返回对应值，再put；没有重复值，直接put，返回null");        System.out.println(sndMap.put("a", 5));        System.out.println(sndMap.put("z", 10086));        System.out.println(sndMap);        System.out.println("=== map.remove(aKey) VS map.remove(aKey, aValue) ===");        System.out.println("map remove(akey)操作：如果有akey，先get返回对应的值，再delete; 否则，返回null");        System.out.println(sndMap.remove("a"));        System.out.println(sndMap.remove("m"));        System.out.println("map remove(aKey, aValue)操作，返回true or false，以表明是否remove成功");        System.out.println(sndMap.remove("b", 2));        System.out.println(sndMap.remove("m", 8));        System.out.println(sndMap);        System.out.println("=== map.clear() ===");        sndMap.clear();        System.out.println(sndMap);    }}
      
     

out：

=== fstMap 输出 ==={a=1, b=2, c=3, d=4}=== aMap.putAll(bMap) ===合并后的sndMap{ab=1, cd=2, a=1, b=2, c=3, d=4}合并后的fstMap剩余{a=1, b=2, c=3, d=4}=== map.getOrDefault(aKey, dV), 有akey则返回相应的值，否则返回dV ===13{ab=1, cd=2, a=1, b=2, c=3, d=4}=== map.put(aKey) 重复key===map put重复值，会先做get，返回对应值，再put；没有重复值，直接put，返回null1null{ab=1, cd=2, a=5, b=2, c=3, d=4, z=10086}=== map.remove(aKey) VS map.remove(aKey, aValue) ===map remove(akey)操作：如果有akey，先get返回对应的值，再delete; 否则，返回null5nullmap remove(aKey, aValue)操作，返回true or false，以表明是否remove成功truefalse{ab=1, cd=2, c=3, d=4, z=10086}=== map.clear() ==={}