如何使用 Java Swing 绘制图形

Question

我正在学习Java Swing。我关注了一个 YouTube 讲座播放列表，该播放列表提供了用于绘制图形的 github 代码。我在这里提供基本结构：

package graphapp;
import com.sun.corba.se.impl.orbutil.graph.Graph;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import javax.swing.JComboBox;
import javax.swing.JFrame;
public class GraphApp extends JFrame {

    int x,y;
    int ax,by;
    JComboBox cb,cb1;
    String s="";
    String se ="";

   public GraphApp(){ 
    setTitle("Graph App");
    setSize(900,700);
    String[] graphs = {"select..","parabola","ax^2+bx+c","ax^3","y=mx","y=mx+c","sin(x)","cos(x)","tan(x)","sinc function","signum(x)","X-graph","cubic         function","sin+cos unequal amp","sin^3","cos^3","sin^3+cos^3","Amplitude Modulation"};
    cb = new JComboBox(graphs);

    cb.setBounds(700, 100, 120, 25);
    add(cb);
    cb.setEditable(false);
    String[] select = {"Draw graph","Erase"};
    cb1 = new JComboBox(select);

    cb1.setBounds(700, 150, 120, 25);
    add(cb1);
    cb1.setEditable(false);

    setLayout(null); //add it its very important otherwise Combo Box will occupy the whole screen.

    setVisible(true);
    setResizable(false);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    x = 30; //x=200;
    y = 300;
}
public void paint(Graphics g){

    super.paint(g); //This method was not called in The Master Branch at github
    g.setColor(Color.BLACK);
    g.drawString("Design by ..", 700, 400);
    g.drawString("Debasish Roy", 700, 420);
    g.drawString("Y", 310, 40);
    g.drawString("Y'", 310, 600);
    g.drawString("X", 30, 314);
    g.drawString("X'", 600, 314);
    if(x==300&&y==300){
        g.drawString("Origin(0,0)", 310, 314);
    }
    g.drawString("Select Graphs", 710, 100);
    g.drawLine(300, 30, 300, 600);
    g.drawLine(30,300,600,300);
    if(x>599||y<40){
        g.drawString((String) cb.getSelectedItem(), 200, 200);
        s= String.valueOf(cb.getSelectedItem());
        se = String.valueOf( cb1.getSelectedItem());
        x=30;
        y=300;

    }                        
    if(s.equals("parabola")&& se.equals("Draw graph")){
        g.setColor(Color.GREEN);
        run1(); // function to set x and y values  
            }
    //Other checks to find the type of graph selected
        else{
        g.setColor(Color.white);
        run();
    }
    g.fillOval(x, y, 3, 3);
    repaint(); // When I run this code, the window keeps flickering. I think it is because this method called without any check.
                //However I don't know much about this method

}

public void run(){
    try{
        Thread.sleep(1);
        if(x<600&&y>30&&y!=600){
             ax = x-300;
             by = y-300;
                  ax++;

                 by = (int) (40*(1+1*Math.cos(.2*ax/3.14))*Math.cos(ax/3.14)+40*(40*Math.sin(.2*ax/3.14))/ax); // AM+sinc(x) function
            x=300+ax;
            y=300-by;

        }

    }catch(Exception e){
        System.out.println("ERROR");
    }
}

public static void main(String[] args){
    new GraphApp();
    Thread t1 = new Thread();
             t1.start();
}

}

当我运行这段代码时，没有绘制任何图形。此外，当我更改 JComboBox 中的选择时，未检测到任何更改。请帮助我在这里抓住我想念的东西。

Answer 1

When I run this code, no graph gets drawn.

您不应覆盖 JFrame 上的 paint(...)。自定义绘画是通过覆盖 JPanel 的 paintComponent(...) 完成的，然后将面板添加到框架中。阅读有关 Custom Painting 的 Swing 教程部分，了解更多信息和工作示例以帮助您入门。
一种绘画方法，仅供绘画使用。你不应该调用 repaint()。 Swing 将确定组件何时需要重新绘制自身或您在外部方法中调用 repaint()。绘制代码应该只绘制组件的当前状态。如果您有更改的属性，那么您需要更改这些属性的方法，然后重新绘制（）组件。
您不应在绘画方法中调用 Thread.sleep()。
您正在创建一个什么都不做的线程。如果要在线程启动时执行代码，则需要将可运行对象传递给线程。但是，在这种情况下，如果您想要图表的动画，那么您应该使用 Swing Timer 作为动画。当计时器触发时，您更新 class 的属性，然后调用 repaint().

Also, when I change selection in JComboBox no change is detected.

您需要向组合框添加一个ActionListener。阅读 How to Use Combo Boxes.

上的 Swing 教程部分

因此您需要花时间阅读 Swing tutorial 以学习一些 Swing 基础知识，然后再继续您的项目。

如何使用 Java Swing 绘制图形

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jframe