java - 调度定时器

Question

我正在使用计时器来帮助模拟重力，并且当基于按键按下来安排计时器时，按键释放会给出一个错误，指出计时器已经安排或取消，我想知道如何解决它。我希望在用户释放空格键时安排一次计时器，并让它连续运行，直到它到达底部或按下空格键。帮助表示赞赏

import java.awt.event.*;
import javax.swing.*;
import java.util.Timer;
import java.util.TimerTask;
import java.util.Calendar;



public class Game implements KeyListener {
    JFrame frame;
    JLabel player;

    public boolean grounded = false;
    public int velocity = 0;
    public int finalY = 0;
    public boolean spaceHeld;
    
    public Timer flightTime;
    public TimerTask flight;
    public Timer gravityTime;
    public TimerTask gravity;


    Action spaceAction;

    Game() {
         
        frame = new JFrame("Nicholas Seow-Xi Crouse");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(1920, 1080);
        frame.setLayout(null);
        
        frame.setFocusable(true);
        frame.addKeyListener(this);

        player = new JLabel();
        player.setBackground(Color.red);
        player.setBounds(10, 800, 50, 50);
        player.setOpaque(true);

        frame.add(player);
        frame.setVisible(true);
        
        flightTime = new Timer();
        flight = new TimerTask() {
         
            public void run() {
                  if(velocity > -5) {
                  velocity -= 1;
                  }
                  else{
                  velocity = -5;
                  }
                  if (finalY < -61) {
                   finalY = finalY + velocity;
                   }
                   else{
                   finalY = -61;
                   }
                   player.setLocation(player.getX(), player.getY() + finalY);
                   if (player.getY() <= 0){
                   cancel();
                   velocity = 0;
                   finalY = 0;
                   player.setLocation(player.getX(), 0);
                    
                   }  
            }
      };
         

         gravityTime = new Timer();
         gravity = new TimerTask() {


            //creates a timer run method that simulates the falling gravity when not grounded
            public void run() {
                if(velocity < 5){
                velocity += 1;
                }
                else{
                velocity = 5;
                }
                //creates the variable the tells where the player is located
                if (finalY < 61) {
                finalY = finalY + velocity;
                }
                else{
                finalY = 61;
                }
                player.setLocation(player.getX(), player.getY() + finalY);
                if (player.getY() >= 1000){
                cancel();
                velocity = 0;
                finalY = 0;
                player.setLocation(player.getX(), 990); 
                }
                
            }
        };

}

public void keyTyped(KeyEvent e) {
}

public void keyPressed(KeyEvent e) {
if(e.getKeyCode() == KeyEvent.VK_SPACE){
if(spaceHeld == false) {
gravity.cancel();
flightTime.scheduleAtFixedRate(flight, 0 ,33);
spaceHeld = true;
}
else {
gravity.cancel();
}
}
            //Cancel the other timer here so they don't overlap
            gravity.cancel();
}


public void keyReleased(KeyEvent e) {
if(e.getKeyCode() == KeyEvent.VK_SPACE){
   gravity.cancel();
   spaceHeld = false;
   flight.cancel();
   gravityTime.scheduleAtFixedRate(gravity, 0, 33);

//Cancel the other timer here so they don't overlap
}
}
}

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