简单的Java 2D图形：绘制一个矩形？

Question

我正在尝试让Java 2D图形“hello world”继续进行，并且发现它非常困难（即，我正在使用Google搜索“java hello world示例”的变体并且空出来）。任何人都可以用最小的hellow世界示例来帮助我吗？

修改

这是一个很好的起点，"The Java Tutorials: Performing Custom Painting"。

Answer 1

要在Swing中绘制一个矩形，你应该：

• 首先，永远不要直接在JFrame或其他顶级窗口中绘图。
• 而是在JPanel，JComponent或最终从JComponent扩展的其他类中绘制。
• 您应该覆盖paintComponent(Graphics g)方法。
• 您应该确保调用超级方法
• 您应该使用JVM提供给方法的Graphics对象绘制矩形。
• 你应该在Swing教程中阅读这幅画。

清除？

如，

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

public class DrawRect extends JPanel {
   private static final int RECT_X = 20;
   private static final int RECT_Y = RECT_X;
   private static final int RECT_WIDTH = 100;
   private static final int RECT_HEIGHT = RECT_WIDTH;

   @Override
   protected void paintComponent(Graphics g) {
      super.paintComponent(g);
      // draw the rectangle here
      g.drawRect(RECT_X, RECT_Y, RECT_WIDTH, RECT_HEIGHT);
   }

   @Override
   public Dimension getPreferredSize() {
      // so that our GUI is big enough
      return new Dimension(RECT_WIDTH + 2 * RECT_X, RECT_HEIGHT + 2 * RECT_Y);
   }

   // create the GUI explicitly on the Swing event thread
   private static void createAndShowGui() {
      DrawRect mainPanel = new DrawRect();

      JFrame frame = new JFrame("DrawRect");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.getContentPane().add(mainPanel);
      frame.pack();
      frame.setLocationByPlatform(true);
      frame.setVisible(true);
   }

   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            createAndShowGui();
         }
      });
   }
}

Answer 2

您需要创建一个从JComponent（或其子类之一，如下例中的JPanel）扩展的类，并覆盖paintComponent(Graphics g)。这是一个例子：

class MyPanel extends JPanel {

    private int squareX = 50;
    private int squareY = 50;
    private int squareW = 20;
    private int squareH = 20;

    protected void paintComponent(Graphics g) {
        super.paintComponent(g); // do your superclass's painting routine first, and then paint on top of it.
        g.setColor(Color.RED);
        g.fillRect(squareX,squareY,squareW,squareH);
    }
}

Answer 3

public void paintComponent(Graphics g) {
    Graphics2D g2 = (Graphics2D) g;
    super.paintComponent(g);
    g2.setColor(Color.red);
    g2.drawRect(10, 10, 100, 100);
}