Map容器大小影响key的索引

单元测试偶然发现的Map一个问题

        Map<String,String> map1 = new HashMap<>();
        map1.put("aaa", "foo");
        map1.put("bbb", "bar");
        map1.put("ccc", "foobar");
        System.out.println(map1); // {aaa=foo, ccc=foobar, bbb=bar}

        Map<String,String> map2 = new HashMap<>(map1);
        assertEquals(map1.values().toArray(new String[]{}), map2.values().toArray(new String[]{}));
        System.out.println(map2); // {aaa=foo, ccc=foobar, bbb=bar}

        Map<String,String> map3 = new HashMap<>(3); //显式指定了大小
        map3.putAll(map1);
        System.out.println(map3); // {bbb=bar, ccc=foobar, aaa=foo}

        assertEquals(map1.values().toArray(new String[]{}), map3.values().toArray(new String[]{})); // 判等失败

可见如果显式指定了map容器大小 会影响key的索引。如下所示

默认大小

key	index
aaa	3
ccc	10
bbb	14

显式指定了大小3

key	index
aaa	3
ccc	2
bbb	2