HashMap引用传递，对象直接赋值，修改的是同一个对象，new HashMap「」(Map)才是生成新的对象

超、凢脫俗 2021-09-23 05:12 462阅读 0赞

**HashMap引用传递；对象直接赋值，修改的是同一个对象**

Map<String, String> srcMap = new HashMap<>();
            srcMap.put("a","a");
    
            Map<String, String> addMap2 = srcMap;
            Map<String, String> removeMap2 = srcMap;
    
            addMap2.put("b","b");
            removeMap2.put("c","c");
    
            System.out.println(srcMap);
            System.out.println(addMap2);
            System.out.println(removeMap2);
            //{a=a, b=b, c=c}
            //{a=a, b=b, c=c}
            //{a=a, b=b, c=c}

**HashMap引用传递：修改的是同一个对象**

Map<String, Map<String, String>> map = new HashMap<>();
            Map<String, String> srcMap = new HashMap<>();
            srcMap.put("a","a");
            srcMap.put("c","c");
            map.put("REMOVE", srcMap);
    
            Map<String, String> srcMap1 = new HashMap<>();
            srcMap1.put("a","a1");
            srcMap1.put("d","d1");
            srcMap.putAll(srcMap1);//合并，key相同时把原值覆盖掉，key不存在时添加
            map.put("ADD", srcMap);
            System.out.println(srcMap);
            System.out.println(srcMap1);
            System.out.println(map);
            //{a=a1, c=c, d=d1}
            //{a=a1, d=d1}
            //{ADD={a=a1, c=c, d=d1}, REMOVE={a=a1, c=c, d=d1}}

**HashMap new 传递：修改不同对象，new HashMap<>(Map)才是生成新的对象**

Map<String, String> srcMap = new HashMap<>();
            srcMap.put("a","a");
            Map<String, String> addMap22 = new HashMap<>(srcMap);
            Map<String, String> removeMap22 =  new HashMap<>(srcMap);;
            addMap22.put("b","b");
            removeMap22.put("c","c");
    
            System.out.println(srcMap);
            System.out.println(addMap22);
            System.out.println(removeMap22);
            //{a=a}
            //{a=a, b=b}
            //{a=a, c=c}

putAll：

Map<String, String> srcMap = new HashMap<>();
            srcMap.put("a","a");
            srcMap.put("c","c");
    
            Map<String, String> srcMap1 = new HashMap<>();
            srcMap1.put("a","a1");
            srcMap1.put("d","d1");
            srcMap.putAll(srcMap1);//合并，key相同时把原值覆盖掉，key不存在时添加
            System.out.println(srcMap);
            System.out.println(srcMap1);
            //{a=a1, c=c, d=d1}
            //{a=a1, d=d1}