Question

java JPanel 中添加文本的问题。

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

class FirstPanel extends JPanel{
public void paintComponent(Graphics q){
q.setColor(Color.red);
q.setFont(new Font("Times New Roman",Font.BOLD,16));
q.drawString("go away!", 120, 90);
}
}
class FirstFrame extends JFrame{
public FirstFrame(){
setTitle("this is title");
setSize(316,216);
FirstPanel fp=new FirstPanel();
add(fp);
fp.setLayout(new FlowLayout(FlowLayout.CENTER));

}

}

public class windows {

public static void main(String[] args){
JFrame frame=new FirstFrame();
//设置用户窗体上执行close的时候使用system.exit方法退出。
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

frame.setVisible(true); //默认的窗口是不可见的。
}

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

class FirstPanel extends JPanel{
public void paintComponent(Graphics q){
q.setColor(Color.red);
q.setFont(new Font("Times New Roman",Font.BOLD,16));
q.drawString("go away!", 120, 90);
}
}
class FirstFrame extends JFrame{
public FirstFrame(){
setTitle("this is title");
setSize(316,216);
FirstPanel fp=new FirstPanel();
add(fp);
fp.setLayout(new FlowLayout(FlowLayout.CENTER));

}

}

public class windows {

public static void main(String[] args){
JFrame frame=new FirstFrame();
//设置用户窗体上执行close的时候使用system.exit方法退出。
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

frame.setVisible(true); //默认的窗口是不可见的。
}

}

这是我的代码，我想让“go away！” 在窗口中居中显示，有没有什么呢方法可以调用的，而不是计算数值，这样肯定不是很准确的居中吧！！

Answer 1

package needl;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import java.util.*;
final class FontColor extends JFrame {
    final static private Dimension SIZE = new Dimension(800, 600);

    public String getTitle() {return "FontColor";}

    public Dimension getPreferredSize() {return SIZE;}

    public Dimension getMinimumSize() {return SIZE;}

    public Dimension getMaximumSize() {return SIZE;}

    public Dimension getSize() {return SIZE;}

    private Canvas canvas;
    private Brush brush;

    FontColor() throws HeadlessException {
        init();
        attachListeners();
        doLay();
        setVisible(true);
    }

    private void init() {
        brush = new StringBoundBrush();
        canvas = new Canvas(brush);
    }

    private void attachListeners() {
        addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent e) {
                System.exit(1);
            }
        });
    }

    private void doLay() {
        Container container = getContentPane();
        container.add(canvas, BorderLayout.CENTER);
        pack();
    }

    public static void main(String... args) {
        System.setProperty("swing.defaultlaf", "com.sun.java.swing.plaf.windows.WindowsLookAndFeel");
        SwingUtilities.invokeLater(FontColor::new);
    }

    private interface Brush extends Observer {
        /**
         * do paint action
         * @param g the graphics context in you application
         */
        void paint(Graphics g);

        /**
         * The component that this brush hold
         * @return component instance
         */
        Component getOwner();

        void setOwner(Component owner);
    }
    private static final class StringBoundBrush implements Brush {
        private Component owner;
        private final static AffineTransform AFFINE_TRANSFORM = AffineTransform.getRotateInstance(45f/180f*Math.PI);
        private final static String CHAR="你好啊！";

        public StringBoundBrush() {
            AFFINE_TRANSFORM.preConcatenate(AffineTransform.getTranslateInstance(100, 100));
        }

        public Component getOwner() {
            return owner;
        }

        public void setOwner(Component owner) {
            this.owner = owner;
        }

        public void paint(Graphics g) {
            Graphics2D g2 = (Graphics2D)g.create();

            g2.setTransform(AFFINE_TRANSFORM);
            g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,RenderingHints.VALUE_ANTIALIAS_ON);
            g2.setColor(Color.PINK);

            g2.setFont(g2.getFont().deriveFont(34f));
            g2.fill( g2.getFontMetrics().getStringBounds(CHAR,g2) );
            g2.setColor(Color.BLUE);
            g2.drawString(CHAR,0,0);
            g2.dispose();
        }

        public void update(Observable o, Object arg) {
            if (owner != null) owner.repaint();
        }
    }
    /**
     * you canvas
     */
    private class Canvas extends JComponent {
        private Brush brush;

        private Canvas(Brush brush) {
            super();
            this.brush = brush;
            brush.setOwner(this);
        }

        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            if (brush == null) return;
            brush.paint(g);
        }
    }
}