Вставка HashMap в HashMap меняет все элементы

package test;
import java.util.HashMap;
 
class Board{
    protected HashMap<String, Integer> Board_Cell = new HashMap<String, Integer>();
    protected HashMap<Integer, HashMap<String, Integer>> Board = new HashMap<Integer, HashMap<String, Integer>>();
    
    public void Generate_Board(){
        this.Board_Cell.put("x", 200);
        this.Board_Cell.put("y", 200);
        this.Board.put(0, this.Board_Cell);
        this.Board_Cell.clear();
        
        this.Board_Cell.put("x", 300);
        this.Board_Cell.put("y", 300);
        this.Board.put(1, this.Board_Cell);
    }
}
 
public class Main {
    public static void main(String[] args) {
        Board board = new Board();
        board.Generate_Board();
        System.out.println(board.Board);
    }
}

{0={y=300, x=300}, 1={y=300, x=300}}

this.Board_Cell.clear();

this.Board_Cell.put("x", 200);
...
this.Board.put(0, this.Board_Cell);
this.Board_Cell.clear();
...
this.Board.put(1, this.Board_Cell);

import java.util.HashMap;
 
class Board {
    protected HashMap<String, Integer> Board_Cell; // = new HashMap<String, Integer>();
    protected HashMap<Integer, HashMap<String, Integer>> b = new HashMap<Integer, HashMap<String, Integer>>();
 
    public void Generate_Board() {
        Board_Cell = new HashMap<String, Integer>();
        this.Board_Cell.put("x", 200);
        this.Board_Cell.put("y", 200);
        this.b.put(0, this.Board_Cell);
        Board_Cell = new HashMap<String, Integer>();
        this.Board_Cell.put("x", 300);
        this.Board_Cell.put("y", 300);
        this.b.put(1, this.Board_Cell);
    }
 
    public static void main(String[] args) {
        Board board = new Board();
        board.Generate_Board();
        System.out.println(board.b);
    }
}