1.集合中的浅拷贝与视图

版权声明：可以转载，转载请注明出处~ https://blog.csdn.net/zhangzhaoyuan30/article/details/89053740

@Test
    public void testCollection() {
        //List<Integer> list = Arrays.asList(1, 2, 3);//不要用这种方式，这种方式生成的是视图
        List<Integer> list = Lists.newArrayList(1, 2, 3);

        HashMap<String, List<Integer>> hashMap1 = new HashMap<>();
        hashMap1.put("aaa", list);

        HashMap<String, List<Integer>> hashMap2 = new HashMap<>(hashMap1);//浅拷贝
        Map<String, List<Integer>> view = Collections.unmodifiableMap(hashMap1);//生成视图

        hashMap1.put("bbb", Arrays.asList(3, 2, 1));

        list.add(4);

        System.out.println(hashMap2);
        System.out.println(view);
    }

以上代码运行结果

{aaa=[1, 2, 3, 4]}
{aaa=[1, 2, 3, 4], bbb=[3, 2, 1]}
 

@Test
    public void test2() {
        HashMap<String, My> hashMap1 = new HashMap<>();
        My my = new My(1);
        hashMap1.put("aa", my);

        HashMap<String, My> hashMap2 = new HashMap<>(hashMap1);

        my.setX(2);

        System.out.println(hashMap1);
        System.out.println(hashMap2);

        my = new My(3);

        System.out.println(hashMap1);
        System.out.println(hashMap2);

        hashMap1.put("aa", new My(4));

        System.out.println(hashMap1);
        System.out.println(hashMap2);
    }

运行结果：

{aa=My{x=2}}
{aa=My{x=2}}
{aa=My{x=2}}
{aa=My{x=2}}
{aa=My{x=4}}
{aa=My{x=2}}

Arrays.copyOf()也是浅拷贝

@Test
    public void test1() {

        CopyOnWriteArrayList<Object> arrayList = new CopyOnWriteArrayList<>();

        My my1 = new My(1);
        My my2 = new My(2);

        My[] myarr = new My[]{my1, my2};
        My[] copy = Arrays.copyOf(myarr, 2);

        my2.setX(3);

        System.out.println(Arrays.toString(myarr));
        System.out.println(Arrays.toString(copy));
    }

[My{x=1}, My{x=3}]
[My{x=1}, My{x=3}]