一 HashMap 不能有多个具有相同属性的元素 key . 尝试使用 ArrayList 取而代之的是：

public class Item implements Comparable<Item>{
    private int num;
    private String name;
    public Item(int num, String name) {
        this.setNum(num);
        this.setName(name);
    }
    public int getNum() {
        return num;
    }
    public void setNum(int num) {
        this.num = num;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    @Override
    public String toString() {
        return "Item [num=" + num + ", name=" + name + "]";
    }
    @Override
    public int compareTo(Item other) {
        return this.num-other.num;
    }
}

List<Item> list=new ArrayList<>();
list.add(new Item(3,"aba"));
list.add(new Item(4,"abab"));
list.add(new Item(3,"aba"));
list.add(new Item(3,"aba"));
Collections.sort(list);
System.out.println(list.toString());

输出：

[Item [num=3, name=aba], Item [num=3, name=aba], Item [num=3, name=aba], Item [num=4, name=abab]]