这个方法只有定义，没有调用，为什么会执行了呢？

[wokaoyan1981]

大家好，我从书上copy了一个绘制饼图的程序，也得到了理想的结果。但是有个问题百思不得其解。PiePanel这个类里面定义了一个名为paintComponent(Graphics comp)的方法，这个方法名没有在其他地方被调用，照理说方法里的内容不会执行的，可是运行后得到了饼图，说明这个方法已经执行了。这是为什么呢？请大佬赐教！代码如下：

package com.java24hours;

import java.awt.*;
import javax.swing.*;
import java.awt.geom.*;

public class PiePanel extends JPanel{
	private PieSlice[] slice;
	private int current=0;
	private float totalSize=0;
	private Color background;
	
	public PiePanel(int sliceCount){
		slice=new PieSlice[sliceCount];
		background=getBackground();
	}
	
	public void addSlice(Color sColor, float sSize){
		if(current<=slice.length){
			slice[current]=new PieSlice(sColor,sSize);
			totalSize+=sSize;
			current++;
		}
	}
	
	public void paintComponent(Graphics comp){
		super.paintComponent(comp);
		Graphics2D comp2D=(Graphics2D) comp;
		int width=getSize().width-10;
		int height=getSize().height-15;
		int xInset=5;
		int yInset=5;
		if(width<5){
			xInset=width;
		}
		if(height<5){
			yInset=height;
		}
		comp2D.setColor(background);
		comp2D.fillRect(0,0,getSize().width,getSize().height);
		comp2D.setColor(Color.lightGray);
		Ellipse2D.Float pie=new Ellipse2D.Float(
				xInset,yInset,width,height);
		comp2D.fill(pie);
		float start=0;
		for(int i=0;i<slice.length;i++){
			float extent=slice[i].size*360F/totalSize;
			comp2D.setColor(slice[i].color);
			Arc2D.Float drawSlice=new Arc2D.Float(
					xInset,yInset,width,height,start,extent,
					Arc2D.Float.PIE);
			start+=extent;
			comp2D.fill(drawSlice);
		}
	}
}

class PieSlice{
	Color color=Color.lightGray;
	float size=0;
	
	PieSlice(Color pColor,float pSize){
		color = pColor;
		size=pSize;
	}

}

package com.java24hours;

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

public class PieFrame extends JFrame{
	Color uneasyBeingGreen=new Color(0xCC,0xCC,0x99);
	Color zuzusPetals=new Color(0xCC,0x66,0xFF);
	Color zootSuit=new Color(0x66,0x66,0x99);
	Color sweetHomeAvocado=new Color(0x66,0x99,0x66);
	Color shrinkingViolet=new Color(0x66,0x66,0x99);
	Color miamiNice=new Color(0x33,0xFF,0xFF);
	Color inBetweenGreen=new Color(0x00,0x99,0x66);
	Color norwegianBlue=new Color(0x33,0xCC,0xCC);
	Color purpleRain=new Color(0x66,0x33,0x99);
	Color freckle=new Color(0x99,0x66,0x33);
	
	public PieFrame(){
		super("Pie Graph");
		setLookAndFeel();
		setSize(320,290);
		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		setVisible(true);
		
		PiePanel pie=new PiePanel(10);
		pie.addSlice(uneasyBeingGreen,1350);
		pie.addSlice(zuzusPetals, 1221);
		pie.addSlice(zootSuit, 316);
		pie.addSlice(sweetHomeAvocado, 251);
		pie.addSlice(shrinkingViolet,201);
		pie.addSlice(miamiNice,193);
		pie.addSlice(inBetweenGreen, 173);
		pie.addSlice(norwegianBlue, 164);
		pie.addSlice(purpleRain, 143);
		pie.addSlice(freckle, 127);
		add(pie);	
	}
	
	private void setLookAndFeel(){
		try{
			UIManager.setLookAndFeel(
					"com.sun.java.swing.plaf.nimbus.NimbusLookAndFeel"
					);
		}catch (Exception exc){
			//ignore error
		}
	}
	
	public static void main(String[] arguments){
		PieFrame pf=new PieFrame();
	}
}

[110成成]

一般窗体绘制或者窗体刷新以及改变大小等操作都会默认执行paintComponent 方法。

[wokaoyan1981]

感谢楼上解答。