求解：关于getInset()的问题

Question

[code]import javax.swing.*;
import javax.swing.event.*;
import java.awt.*;public class ColorSlide extends JFrame implements ChangeListener{
        ColorPanel canvas=new ColorPanel();
        JSlider red=new JSlider(0,255,255);
        JSlider green=new JSlider(0,255,0);
        JSlider blue=new JSlider(0,255,0);
        
        public ColorSlide(){
                super("Color Slide");
                setSize(270,300);
                setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                setVisible(true);
                
                red.setMajorTickSpacing(50);
                red.setMinorTickSpacing(10);
                red.setPaintTicks(true);
                red.setPaintLabels(true);
                red.addChangeListener(this);
                
                green.setMajorTickSpacing(50);
                green.setMinorTickSpacing(10);
                green.setPaintTicks(true);
                green.setPaintLabels(true);
                green.addChangeListener(this);
                
                blue.setMajorTickSpacing(50);
                blue.setMinorTickSpacing(10);
                blue.setPaintTicks(true);
                blue.setPaintLabels(true);
                blue.addChangeListener(this);
                
                JLabel redLabel=new JLabel("Read:");
                JLabel greenLabel=new JLabel("Green:");
                JLabel blueLabel=new JLabel("Blue:");
                GridLayout grid=new GridLayout(4,1);
                FlowLayout right=new FlowLayout(FlowLayout.RIGHT);
                setLayout(grid);
                
                JPanel redPanel=new JPanel();
                redPanel.setLayout(right);
                redPanel.add(redLabel);
                redPanel.add(red);
                add(redPanel);
                
                JPanel greenPanel=new JPanel();
                greenPanel.setLayout(right);
                greenPanel.add(greenLabel);
                greenPanel.add(green);
                add(greenPanel);
                
                JPanel bluePanel=new JPanel();
                bluePanel.setLayout(right);
                bluePanel.add(blueLabel);
                bluePanel.add(blue);
                add(bluePanel);
                add(canvas);
                
                setVisible(true);
        }
        
        public void stateChanged(ChangeEvent evt){
                JSlider source=(JSlider)evt.getSource();
                if(source.getValueIsAdjusting()!=true){
                        Color current=new Color(red.getValue(),green.getValue(),blue.getValue());
                        canvas.changeColor(current);
                        canvas.repaint();
                }
        }
        
        public Insets getInsets(){
                Insets border=new Insets(45,10,10,10);
                return border;
        }
        
        public static void main(String[] arguments){
                ColorSlide cs=new ColorSlide();
        }
}class ColorPanel extends JPanel{
        Color background;
        
        ColorPanel(){
                background=Color.red;
        }
        
        public void paintComponent(Graphics comp){
                Graphics2D comp2D=(Graphics2D)comp;
                comp2D.setColor(background);
                comp2D.fillRect(0,0,getSize().width,getSize().height);
        }
        
        void changeColor(Color newBackground){
                background=newBackground;
        }
}[/code]
       可以在代码看到getInsets()是被创建了，但没调用，可通过修改边界值（如改为：45，10，45，10）就能发现实际上是被调用了的，那是怎么被调用了？
       还有就是，既然有了getInsets()方法，怎么没有setInsets()方法呢？

Answer 1

代码如下：import javax.swing.*;
import javax.swing.event.*;
import java.awt.*;public class ColorSlide extends JFrame implements ChangeListener{
        ColorPanel canvas=new ColorPanel();
        JSlider red=new JSlider(0,255,255);
        JSlider green=new JSlider(0,255,0);
        JSlider blue=new JSlider(0,255,0);
        
        public ColorSlide(){
                super("Color Slide");
                setSize(270,300);
                setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                setVisible(true);
                
                red.setMajorTickSpacing(50);
                red.setMinorTickSpacing(10);
                red.setPaintTicks(true);
                red.setPaintLabels(true);
                red.addChangeListener(this);
                
                green.setMajorTickSpacing(50);
                green.setMinorTickSpacing(10);
                green.setPaintTicks(true);
                green.setPaintLabels(true);
                green.addChangeListener(this);
                
                blue.setMajorTickSpacing(50);
                blue.setMinorTickSpacing(10);
                blue.setPaintTicks(true);
                blue.setPaintLabels(true);
                blue.addChangeListener(this);
                
                JLabel redLabel=new JLabel("Read:");
                JLabel greenLabel=new JLabel("Green:");
                JLabel blueLabel=new JLabel("Blue:");
                GridLayout grid=new GridLayout(4,1);
                FlowLayout right=new FlowLayout(FlowLayout.RIGHT);
                setLayout(grid);
                
                JPanel redPanel=new JPanel();
                redPanel.setLayout(right);
                redPanel.add(redLabel);
                redPanel.add(red);
                add(redPanel);
                
                JPanel greenPanel=new JPanel();
                greenPanel.setLayout(right);
                greenPanel.add(greenLabel);
                greenPanel.add(green);
                add(greenPanel);
                
                JPanel bluePanel=new JPanel();
                bluePanel.setLayout(right);
                bluePanel.add(blueLabel);
                bluePanel.add(blue);
                add(bluePanel);
                add(canvas);
                
                setVisible(true);
        }
        
        public void stateChanged(ChangeEvent evt){
                JSlider source=(JSlider)evt.getSource();
                if(source.getValueIsAdjusting()!=true){
                        Color current=new Color(red.getValue(),green.getValue(),blue.getValue());
                        canvas.changeColor(current);
                        canvas.repaint();
                }
        }
        
        public Insets getInsets(){
                Insets border=new Insets(45,10,10,10);
                return border;
        }
        
        public static void main(String[] arguments){
                ColorSlide cs=new ColorSlide();
        }
}class ColorPanel extends JPanel{
        Color background;
        
        ColorPanel(){
                background=Color.red;
        }
        
        public void paintComponent(Graphics comp){
                Graphics2D comp2D=(Graphics2D)comp;
                comp2D.setColor(background);
                comp2D.fillRect(0,0,getSize().width,getSize().height);
        }
        
        void changeColor(Color newBackground){
                background=newBackground;
        }
}