Java 加載圖片的兩種方法

1.使用Toolkit.getDefaultToolkit().getImage()方法

View Code 

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

public class TestLoadImage{
    public static void main(String[] args){
        JFrame f=new JFrame();
        MyCanvas mc=new MyCanvas();
        Image image=Toolkit.getDefaultToolkit().getImage("a.PNG");
        mc.setImage(image);
        f.add(mc);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setSize(400,550);
        f.setVisible(true);
    }
}

class MyCanvas extends Canvas {
    private Image in;
    private int image_width;
    private int image_height;
    
    public void setImage(Image in){
        this.in=in;
    }
    
    public void paint(Graphics g){
        g.drawImage(in,0,0,this.getWidth(),this.getHeight(),this);
    }    
}

 

2.使用BufferedImage類加載，BufferedImage類基礎了Image類

View Code 

import java.awt.*;
import java.awt.image.*;
import javax.swing.JFrame;
import java.io.*;
import javax.imageio.*;


public class TestBufferedImage extends Canvas{
    
    public static void main(String[] args){
        JFrame f=new JFrame();
        MyCanvas mc=new MyCanvas();
        f.add(mc);
        try{
            File file=new File("a.PNG");
            BufferedImage bi=ImageIO.read(file);
            mc.setImage(bi);
        }catch(Exception e){
            e.printStackTrace();
        }
        mc.repaint();
        f.setSize(400,550);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setVisible(true);
    }
}

class MyCanvas extends Canvas{
    private BufferedImage bi;
    private Image im;
    private int image_width;
    private int image_height;
    
    public void setImage(BufferedImage bi){
        this.bi=bi;
        this.zoom();
    }
    
    public void paint(Graphics g){
        g.drawImage(im,0,0,this.getWidth(),this.getHeight(),this);
    }
    
    public void zoom(){
        image_width=bi.getWidth();
        image_height=bi.getHeight();
        im=bi.getScaledInstance(image_width,image_height,Image.SCALE_SMOOTH);
    }
}

 

兩種方法都會遇到一個問題，就是隨着窗口改變，圖片大小固定不變，要想實現圖片隨窗口大小改變，只需要

g.drawImage(im,0,0,this.getWidth(),this.getHeight(),this);

 

在使用BufferedImage加載圖片時需要調用其getScaledInstance()方法創建一個新Image對象，否則圖像無法顯示在畫布上。