将action方法移至FishAnimation类后Java Swing动画失效求助

将原本在Screen类中的动画action方法剪切到FishAnimation类后，调用fA.action()完全看不到动画效果，但把方法移回Screen类就正常运行，请问原因是什么？

Screen类代码 #

package main;

import java.awt.Dimension;
import java.io.IOException;
import javax.swing.JFrame;
import javax.swing.JLayeredPane;
import javax.swing.JPanel;
import AnimatorHandler.FishAnimation;
import data.*;
import save.Data;

public class Screen extends JPanel{
    
    Resources res = new Resources();
    Background background = new Background();
    Ground ground = new Ground();
    Animal animal = new Animal(null, null, 0, null, 0, 0);
    FishAnimation fA = new FishAnimation();
    
    int screenSizeX = 1099;
    int screenSizeY = 735;
    
    void createWindow() throws IOException {
        
        //CREATION OF THE RESOURCES
        background.createBackground();
        ground.createGround();
        animal.createAnimal();
        
        //SETTING OF THE LAYEREDPANE
        JLayeredPane layeredPane = new JLayeredPane();
        layeredPane.setBounds(0, 0, screenSizeX, screenSizeY);
        layeredPane.add(background.background[Data.selectedBackground], Integer.valueOf(0));
        layeredPane.add(ground.ground[Data.selectedGround], Integer.valueOf(1));
        layeredPane.add(animal.animals[Data.selectedAnimal], Integer.valueOf(2));
        layeredPane.add(animal.animals[Data.selectedAnimal+1], Integer.valueOf(2));
           
        //SETTING OF THE FRAME
        JFrame frame = new JFrame("Happy Aquarium");
        frame.add(layeredPane);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(new Dimension(screenSizeX, screenSizeY));
        frame.setLayout(null);
        frame.setVisible(true);
        
        //ANIMATION
        fA.action();
        
    }
}

FishAnimation类代码 #

package AnimatorHandler;

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.IOException;

import javax.swing.Timer;

import data.Animal;
import save.Data;

public class FishAnimation implements ActionListener{
    
    Animal animal = new Animal(null, null, 0, null, 0, 0);
    Timer timer;
    
    public void action() throws IOException {
        animal.createAnimal();
        
        timer = new Timer(1, this);
        timer.start();
            
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        
        if(animal.animals[Data.selectedAnimal].getY() >= 260 || animal.animals[Data.selectedAnimal].getY()<-300) {
            animal.animali[Data.selectedAnimal].setYVelocity(animal.animali[Data.selectedAnimal].getYVelocity() * -1);
        }
        
        if(animal.animals[Data.selectedAnimal].getX() >= 456 || animal.animals[Data.selectedAnimal].getX()<-456) {
            animal.animali[Data.selectedAnimal].setXVelocity(animal.animali[Data.selectedAnimal].getXVelocity() * -1);
        }
        animal.animals[Data.selectedAnimal].setBounds(animal.animals[Data.selectedAnimal].getX() + animal.animali[Data.selectedAnimal].getXVelocity(), animal.animals[Data.selectedAnimal].getY() + animal.animali[Data.selectedAnimal].getYVelocity(), 1083, 696);

        if(animal.animals[Data.selectedAnimal+1].getY() >= 260 || animal.animals[Data.selectedAnimal+1].getY()<-300) {
            animal.animali[Data.selectedAnimal+1].setYVelocity(animal.animali[Data.selectedAnimal+1].getYVelocity() * -1);
        }
        
        if(animal.animals[Data.selectedAnimal+1].getX() >= 456 || animal.animals[Data.selectedAnimal+1].getX()<-456) {
            animal.animali[Data.selectedAnimal+1].setXVelocity(animal.animali[Data.selectedAnimal+1].getXVelocity() * -1);
        }
        animal.animals[Data.selectedAnimal+1].setBounds(animal.animals[Data.selectedAnimal+1].getX() + animal.animali[Data.selectedAnimal+1].getXVelocity(), animal.animals[Data.selectedAnimal+1].getY() + animal.animali[Data.selectedAnimal+1].getYVelocity(), 1083, 696);
        
    }
}

原因分析 #

核心问题是操作的对象不一致：

• Screen类中创建了一个Animal实例，调用animal.createAnimal()后，将这个实例的动物组件添加到了UI的分层面板中，是界面上显示的真实对象。
• FishAnimation类内部自己new了一个全新的Animal实例，这个实例和Screen里的不是同一个对象，它的组件从未被添加到界面上。
• FishAnimation的actionPerformed方法一直在修改自己内部这个"隐形"的Animal实例的属性，界面上的真实组件完全没被改动，所以看不到动画效果；而原来在Screen类中时，操作的是同一个被添加到UI的Animal实例，所以动画正常。

修复方案 #

1. 修改FishAnimation类，接收外部传入的Animal实例 #

去掉内部自己创建的Animal，通过构造方法传入Screen中的实例：

package AnimatorHandler;

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.IOException;

import javax.swing.Timer;

import data.Animal;
import save.Data;

public class FishAnimation implements ActionListener{
    
    private Animal animal; // 改为外部传入
    Timer timer;
    
    // 新增构造方法，接收Animal实例
    public FishAnimation(Animal animal) {
        this.animal = animal;
    }
    
    public void action() throws IOException {
        // 移除animal.createAnimal()，因为Screen中已经初始化过
        timer = new Timer(1, this);
        timer.start();
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        // 方法内容保持不变，现在操作的是界面上的真实Animal实例
        if(animal.animals[Data.selectedAnimal].getY() >= 260 || animal.animals[Data.selectedAnimal].getY()<-300) {
            animal.animali[Data.selectedAnimal].setYVelocity(animal.animali[Data.selectedAnimal].getYVelocity() * -1);
        }
        
        if(animal.animals[Data.selectedAnimal].getX() >= 456 || animal.animals[Data.selectedAnimal].getX()<-456) {
            animal.animali[Data.selectedAnimal].setXVelocity(animal.animali[Data.selectedAnimal].getXVelocity() * -1);
        }
        animal.animals[Data.selectedAnimal].setBounds(animal.animals[Data.selectedAnimal].getX() + animal.animali[Data.selectedAnimal].getXVelocity(), animal.animals[Data.selectedAnimal].getY() + animal.animali[Data.selectedAnimal].getYVelocity(), 1083, 696);

        if(animal.animals[Data.selectedAnimal+1].getY() >= 260 || animal.animals[Data.selectedAnimal+1].getY()<-300) {
            animal.animali[Data.selectedAnimal+1].setYVelocity(animal.animali[Data.selectedAnimal+1].getYVelocity() * -1);
        }
        
        if(animal.animals[Data.selectedAnimal+1].getX() >= 456 || animal.animals[Data.selectedAnimal+1].getX()<-456) {
            animal.animali[Data.selectedAnimal+1].setXVelocity(animal.animali[Data.selectedAnimal+1].getXVelocity() * -1);
        }
        animal.animals[Data.selectedAnimal+1].setBounds(animal.animals[Data.selectedAnimal+1].getX() + animal.animali[Data.selectedAnimal+1].getXVelocity(), animal.animals[Data.selectedAnimal+1].getY() + animal.animali[Data.selectedAnimal+1].getYVelocity(), 1083, 696);
    }
}

2. 修改Screen类，初始化FishAnimation时传入自己的Animal实例 #

package main;

import java.awt.Dimension;
import java.io.IOException;
import javax.swing.JFrame;
import javax.swing.JLayeredPane;
import javax.swing.JPanel;
import AnimatorHandler.FishAnimation;
import data.*;
import save.Data;

public class Screen extends JPanel{
    
    Resources res = new Resources();
    Background background = new Background();
    Ground ground = new Ground();
    Animal animal = new Animal(null, null, 0, null, 0, 0);
    FishAnimation fA; // 先声明，后初始化
    
    int screenSizeX = 1099;
    int screenSizeY = 735;
    
    void createWindow() throws IOException {
        
        //CREATION OF THE RESOURCES
        background.createBackground();
        ground.createGround();
        animal.createAnimal();
        
        // 初始化FishAnimation时传入当前的animal实例
        fA = new FishAnimation(animal);
        
        //SETTING OF THE LAYEREDPANE
        JLayeredPane layeredPane = new JLayeredPane();
        layeredPane.setBounds(0, 0, screenSizeX, screenSizeY);
        layeredPane.add(background.background[Data.selectedBackground], Integer.valueOf(0));
        layeredPane.add(ground.ground[Data.selectedGround], Integer.valueOf(1));
        layeredPane.add(animal.animals[Data.selectedAnimal], Integer.valueOf(2));
        layeredPane.add(animal.animals[Data.selectedAnimal+1], Integer.valueOf(2));
           
        //SETTING OF THE FRAME
        JFrame frame = new JFrame("Happy Aquarium");
        frame.add(layeredPane);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(new Dimension(screenSizeX, screenSizeY));
        frame.setLayout(null);
        frame.setVisible(true);
        
        //ANIMATION
        fA.action();
        
    }
}

内容的提问来源于stack exchange，提问作者TokenZ