java - Java JFrame大小不正确

我正在尝试为游戏编程，但是我无法完全打开所需的大窗口。
第一个println给我720，第二个732给我，窗口实际上大于720。
如何使游戏显示的高度恰好为720像素？

xCopterGame.java

import javax.swing.JFrame;
import java.awt.Dimension;
import java.awt.event.*;

public class xCopterGame extends JFrame implements MouseListener{

  private static final long serialVersionUID = 1L;

  Board panel=null;
  public xCopterGame(){
    panel = new Board();
    setTitle("Pong");
    setDefaultCloseOperation(DISPOSE_ON_CLOSE);
    panel.setPreferredSize(new Dimension(1280,720));
    getContentPane().add(panel);
    pack();
    setLocationRelativeTo(null);
    setVisible(true);
    setResizable(false);

    System.out.println(panel.getHeight());

    panel.yCopter = getHeight()/2-15;

    panel.addMouseListener(this);
    addMouseListener(this);
  }

  public void mousePressed(MouseEvent e) {
    panel.mousePressed(e);
  }

  public void mouseReleased(MouseEvent e) {
    panel.mouseReleased(e);
  }

  public static void main(String[] args) {
    new xCopterGame();
  }


  public void mouseClicked(MouseEvent e) {

  }
  public void mouseEntered(MouseEvent e) {

  }
  public void mouseExited(MouseEvent e) {

  }
}

Board.java

import java.awt.Color;
import java.awt.Graphics;
import java.awt.event.MouseEvent;
import javax.swing.JPanel;

public class Board extends JPanel implements Runnable{
  private static final long serialVersionUID = 1L;

  Thread th=null;
  boolean mousePressed = false, firstClick = false;
  int yCopter;

  public Board(){
    th = new Thread(this);
    th.start();
  }

  public void paint(Graphics g){
    super.paint(g);
    this.setBackground(Color.black);
    g.setColor(Color.white);
    g.fillRect(80, yCopter, 30, 30);

    g.setColor(Color.gray);
    for(int i=0; i<37; i++){
      g.drawLine(0, i*20, this.getWidth(), i*20);
    }

    g.fillRect(100, 715, 30, 5);
    g.fillRect(100, 0, 30, 5);
    System.out.println(this.getHeight());
  }

  public void run() {
    while(true){
      if(mousePressed == true)
        yCopter--;
      if(mousePressed == false && firstClick == true)
        yCopter++;

   //   repaint();

      try {
        Thread.sleep(10);
      }
      catch(InterruptedException ex) {

      }
    }
  }

  public void mousePressed(MouseEvent e) {
    mousePressed = true;
    firstClick = true;
  }
  public void mouseReleased(MouseEvent e) {
    mousePressed = false;
  }
}

最佳答案

setResizable()可能会影响帧的插图。最好在setResizable()之后调用pack（）。尝试以下呼叫顺序：

setResizable(false);
pack();
setVisible(true);

供参考，请参阅@HovercraftFullOfEels的this分析

您可能还会发现Should I avoid the use of set[Preferred|Maximum|Minimum]Size methods in Java Swing?有用。