import java.awt.AlphaComposite;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JComponent;
import javax.swing.Timer;

public abstract class Page extends JComponent implements ActionListener{
    private static final long serialVersionUID = -1071441396934207094L;

    // 帧总量
    private static final int FRAMES_COUNT=10;  

    // Timer的时间间隔
    private static final int INTERVAL=50;  

    // 定时器
    private Timer timer;

    // 每次递增或递减的值
    private int offset=0;

    //帧索引
    private int frameIndex; 

    public void paint(Graphics g){
        if(isTimerRunning()){
            //根据当前帧显示当前透明度的内容组件
            float alpha=(float)frameIndex/(float)FRAMES_COUNT;
            Graphics2D g2d=(Graphics2D)g;
            g2d.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER, alpha));
            //Renderer渲染机制
            super.paint(g2d);
        }else{
            super.paint(g);
        }
    }  

    @Override
    public void actionPerformed(ActionEvent e) {
        //前进一帧
        frameIndex+=offset;
        if(frameIndex>=FRAMES_COUNT || frameIndex<=0){
            //最后一帧，关闭动画
            closeTimer();
        }
        else{
            //更新当前一帧
            repaint();
        }
    }

    // 淡出
    public boolean fadeOut(){
        offset=-1;
        frameIndex=FRAMES_COUNT;

        timer=new Timer(INTERVAL,this);
        timer.start();

        return true;
    }

    // 淡入
    public boolean fadeIn(){
        offset=1;
        frameIndex=0;

        timer=new Timer(INTERVAL,this);
        timer.start();

        return true;
    }

    // 关闭定时器
    protected void closeTimer(){
        if(isTimerRunning()){
            timer.stop();
            timer=null;
        }

    }

    // 判断定时器是否处于工作状态
    public boolean isTimerRunning(){
        return timer!=null && timer.isRunning();
    }
}