JComponent未出现在JApplet中

Question

我已经成功构建了一个JComponent饼图，它位于它自己独立的类IAPieChart.java中。 PieChart逻辑位于一个扩展JComponent的静态内部类中。 JApplet本身构建良好并显示'我在这里！'表示使用此代码构建和添加面板：

public class IAPieChartApplet extends JApplet {

     JPanel controls;
     JPanel chartPanel;
     JComponent pieChart;

    /**
     * Initialization method that will be called after the Applet is loaded into
     * the browser.
     */

    public void init() {

        // Build the Pie Chart Panel
        buildPieChartPanel();

        // Build the controls panel
        buildControlsPanel();

        //Set the Layout
        setLayout(new FlowLayout());

        //getContentPane().add(new PieChart(), controls);
        //add(chartPanel);
        //add(controls);

    }



    private void buildPieChartPanel(){

        // Build the panel JPanel
        chartPanel = new JPanel();
        pieChart = new PieChart();
        JLabel label = new JLabel("Here I Am!");
        chartPanel.add(pieChart);
        chartPanel.add(label);

    }

    private void buildControlsPanel() {

        controls = new JPanel();
        JLabel here = new JLabel("Here I Am");
        controls.add(here);

    }

}

当我运行这个IAPieChartApplet.java文件时，我得到标签而没有PieChart。

我在这里设置了一个方法断点并进入静态PieChart类：

private void buildPieChartPanel(){

        // Build the panel JPanel
        chartPanel = new JPanel();
        pieChart = new PieChart();
        JLabel label = new JLabel("Here I Am!");
        chartPanel.add(pieChart);
        chartPanel.add(label);

    }

Debug将我带到这里，然后退出课堂。它确实逐步完成了PieChart类中的其余逻辑。这是PieChart静态类的代码，再次运行正常。调试将带我到IAPieChart数组，然后退出该方法。这可能是'为什么'它没有显示的原因。

这是PieChart类代码：

public static class PieChart extends JComponent { 

        IAPieChart[] pieValue = {new IAPieChart(2, Color.green),
                                new IAPieChart(4, Color.orange),
                                new IAPieChart(4, Color.blue),
                                new IAPieChart(3, Color.red)

        };

        public void paintComponent(Graphics g) {

            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g; 
            g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, 
                    RenderingHints.VALUE_ANTIALIAS_ON);
            drawPie((Graphics2D) g, getBounds(),  pieValue);

        }

        void drawPie(Graphics2D g, Rectangle area, IAPieChart[] pieValue){

            double sum = 0.0;
            for (int i = 0; i < pieValue.length; i++) {

                sum += pieValue[i].arcValue;
            }
            // DONT NEED endPoint to make the pieChart (Mishadoff's sample). 
            // needs double endPoint = 0.0D for (phcoding's sample).
            double endPoint =  0.0D;
            int arcStart = 0; 
            for (int i = 0; i < pieValue.length; i++){

                /////////THIS IS THE OLD STATEMENT////////
                //endPoint += (int) (endPoint * 360 / sum);
                arcStart = (int) (endPoint * 360 / sum);

                // this statement makes the pieChart.
                int radius = (int) (pieValue[i].arcValue * 360/ sum);
                g.setColor(pieValue[i].color);
                //g.fillArc(area.x, area.y, area.width, area.height, arcStart , radius);
                g.fillArc(area.x, area.y, area.width, area.height, arcStart , radius);

                ///////THIS IS THE OLD STATEMENT////
                //arcStart += pieValue[i].arcValue;
                endPoint += pieValue[i].arcValue;

                // this statement will make the pieChart.
                //arcStart += radius;
            }

        }
    }   // END PieChart class.*

我尝试过使用getContentPane（），repaint（）以及其他在搜索中看起来不错的东西，而我只是选择了。过去几周我一直表现不错，但这项任务一直困扰着我。我希望你能提供帮助。

Answer 1

饼图未显示为PieChart没有任何首选尺寸。因此，使用默认JPanel的包含FlowLayout不会显示它。应getPreferredSize使用setPreferredSize：

@Override
public Dimension getPreferredSize() {
   return new Dimension(100, 100);
}

更新

在您修改的小程序中，您正在扩展未覆盖Applet的旧AWT paintComponent，而是使用JApplet。

Answer 2

我已尽最大努力重做程序，使用给出的建议，图片仍然不会显示在applet中。在摆脱实例化错误后，我得到了applet以便成功构建，但饼图不会显示。我希望有人能帮忙解决这个问题，以便我可以继续使用这个程序。

以下是我现在所拥有的：

package iapiechart;

import java.applet.Applet;
import java.awt.*;
import javax.swing.JComponent;

public class IAPieChart2 extends Applet
{
   double arcValue;        // passes a value for the calculation of the arc.
    Color color;            // holds value for color (expressed as an integer
    public IAPieChart2(){};
    public IAPieChart2(double value, Color color){

        arcValue = value;
        this.color = color;
    } 

    public  class PieChart extends JComponent { 

        public PieChart(){};

        IAPieChart[] pieValue = {new IAPieChart(2, Color.green),
                                new IAPieChart(4, Color.orange),
                                new IAPieChart(4, Color.blue),
                                new IAPieChart(3, Color.red)

        };
        @Override
    public void paintComponent(Graphics g) {

            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g; 
            g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, 
                    RenderingHints.VALUE_ANTIALIAS_ON);
            drawPie((Graphics2D) g, getBounds(),  pieValue);

        }
    void drawPie(Graphics2D g, Rectangle area, IAPieChart[] pieValue){

            double sum = 0.0;
            for (int i = 0; i < pieValue.length; i++) {

                sum += pieValue[i].arcValue;
            }
            // DONT NEED endPoint to make the pieChart (Mishadoff's sample). 
            // needs double endPoint = 0.0D for (phcoding's sample).
            double endPoint =  0.0D;
            int arcStart = 0; 
            for (int i = 0; i < pieValue.length; i++){

                /////////THIS IS THE OLD STATEMENT////////
                //endPoint += (int) (endPoint * 360 / sum);
                arcStart = (int) (endPoint * 360 / sum);

                // this statement makes the pieChart.
                int radius = (int) (pieValue[i].arcValue * 360/ sum);
                g.setColor(pieValue[i].color);
                //g.fillArc(area.x, area.y, area.width, area.height, arcStart , radius);
                g.fillArc(area.x, area.y, area.width, area.height, arcStart , radius);

                endPoint += pieValue[i].arcValue;

            }
    }
    }
    @Override
    public void init(){

        IAPieChart2 iap2 = new IAPieChart2();
        PieChart pc = new PieChart();
        setPreferredSize(new Dimension(300, 200));
        iap2.getPreferredSize();
        super.add(pc);
        setVisible(true);

    }

}