Question

我正在尝试使用eclipse在java中绘制一些矩形，并且调用draw()方法会给我一个错误。我在这里缺少什么吗？

import java.awt.Rectangle;

public class UsingRectangle {
    public static void main(String[] args) {
        Rectangle box1 = new Rectangle(0, 0, 20, 30);

        //error "The method draw() is undefined for the type Rectangle"
        box1.draw();
    }
}

任何帮助都不仅仅是值得赞赏的。谢谢。

Answer 1

首先阅读：

Rectangle是形状的表示，它本身没有如何绘画的概念，但可以通过适当的API绘制

Rectangle

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class PaintRectangle {

    public static void main(String[] args) {
        new PaintRectangle();
    }

    public PaintRectangle() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                }

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        private Rectangle box1;

        public TestPane() {
            box1 = new Rectangle(0, 0, 20, 30);
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(200, 200);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();
            g2d.setColor(Color.RED);
            g2d.fill(box1);
            g2d.setColor(Color.BLUE);
            g2d.draw(box1);
            g2d.dispose();
        }
    }

}

Answer 2

这是绘制矩形的方法。在您发布问题之前谷歌有点：）

// Draw rectangles
import java.awt.*;
import java.applet.*;

public class Rectangles extends Applet {
    public void paint(Graphics g) {
        g.drawRect(10, 10, 60, 50);
        g.fillRect(100, 10, 60, 50);
        g.drawRoundRect(190, 10, 60, 50, 15, 15);
        g.fillRoundRect(70, 90, 140, 100, 30, 40);
    }
}

编辑：Java The complete reference Herbert Schildt

取自{{1}}的示例

Answer 3

你想要它画在哪里？查看你正在使用main的代码，它将在控制台中输出，实际上是main而不扩展特殊类，如JFrame（这是你需要的，因为这是你可以绘制的地方，这是java中的一个窗口）

请参阅下面的代码，了解绘制矩形的其他方法。

import java.awt.Graphics;
import javax.swing.JComponent;
import javax.swing.JFrame;

class UsingRectangle extends JComponent {

  public void paint(Graphics g) {
    g.drawRect (10, 10, 200, 200);  
  }
}

public class DrawRect {
  public static void main(String[] a) {
    JFrame window = new JFrame();
    window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    window.setBounds(30, 30, 300, 300);
    window.getContentPane().add(new UsingRectangle());
    window.setVisible(true);
  }
}

或使用paintComponent

import java.awt.Container;
import java.awt.Graphics;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class UsingRectangle extends JPanel {
  public void paintComponent(Graphics g) {
    super.paintComponent(g);
    g.drawRectangle (10, 10, 200, 200);  
  }
  public static void main(String[] args) {
    JFrame frame = new JFrame();
    frame.setSize(300, 200);
    frame.addWindowListener(new WindowAdapter() {
      public void windowClosing(WindowEvent e) {
        System.exit(0);
      }
    });
    Container contentPane = frame.getContentPane();
    contentPane.add(new UsingRectangle());
    frame.show();
  }
}

另请参阅this了解paint和paintComponent之间的差异，以供将来参考。

我们必须导入一些东西来使用draw（）吗？

3 个答案: