在HashMap中将值从一个关键点移动到另一个关键点

Question

我有一个保存学生对象的ArrayList，如下所示：

List<Students> stdList = new ArrayList<Students>();
stdList.add(new Students(1,"std1","address1"));
stdList.add(new Students(2,"std2","address2"));
stdList.add(new Students(3,"std3","address3"));
stdList.add(new Students(4,"std4","address4"));
stdList.add(new Students(5,"std5","address5"));
stdList.add(new Students(6,"std6","address6"));
stdList.add(new Students(7,"std7","address7"));
stdList.add(new Students(8,"std8","address8"));

现在，我需要将stdList分成两组，在本例中包含相等的学生数，即4，并将它们添加到hashMap中，这是通过以下方法实现的：

 int j=0;
 HashMap<Integer,List<Students>> hm = new HashMap<>();
    for (int i = 0; i < stdList.size(); i = i + 4) 
  {
     j++;
     hm.put(j,stdList.subList(i, i + 4));

  }

哈希图现在包含键值对，如下所示：

{1=[1 std1 address1, 2 std2 address2, 3 std3 address3, 4 std4 address4], 2=[5 std5 address5, 6 std6 address6, 7 std7 address7, 8 std8 address8]}

现在我需要将一个值"3 std3 address3“从"key 1”移动到"key 2“，如下所示：

{1=[1 std1 address1, 2 std2 address2,  4 std4 address4], 2=[5 std5 address5, 6 std6 address6, 7 std7 address7, 8 std8 address8,3 std3 address3]}

我如何才能做到这一点？

Answer 1

假设"someKey“是您要删除的密钥，那么

key1.put(someKey, key2.remove(someKey));

Answer 2

List<Student> ls = hm.get(1);
Student st  = ls.get(3);
ls.remove(st); hm.get(2).add(st);

如果可以通过索引访问列表，则不需要搜索列表。

Answer 3

解决方案是从HashMap中获取学生列表，然后删除要移动的学生对象。然后从HashMap获取另一个列表，只需添加对象即可。

我没有运行下面的代码，但它应该是这样的

//Get the list for Key 1
List<Students> list = hm.get(Integer.valueOf(1));

//Remove the 3rd value, that would be your "3 std3 address3"
Students std = list.remove(2);

//Now get the list of Key 2
list = hm.get(Integer.valueOf(2));

//Add the value to that list
list.add(std);