JFreeChart从另一个JDialog接收公式生成；AWT-EventQueue-0“；java.lang.NullPointerException

问题是，在将整个方程发送到JFreeChart时遇到问题，我试图只发送x^3，x^2的参数。。。等等

尽管如此，我还是得到了一个错误：

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at calc.kalkulator.OknoFunkcji.getDane(OknoFunkcji.java:24)
at calc.kalkulator.OknoFunkcji.<init>(OknoFunkcji.java:37)
at calc.kalkulator.PanelFunkcji.actionPerformed(PanelFunkcji.java:103)
at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
at java.awt.Component.processMouseEvent(Unknown Source)
at javax.swing.JComponent.processMouseEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$200(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.WaitDispatchSupport$2.run(Unknown Source)
at java.awt.WaitDispatchSupport$4.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.awt.WaitDispatchSupport.enter(Unknown Source)
at java.awt.Dialog.show(Unknown Source)
at java.awt.Component.show(Unknown Source)
at java.awt.Component.setVisible(Unknown Source)
at java.awt.Window.setVisible(Unknown Source)
at java.awt.Dialog.setVisible(Unknown Source)
at calc.kalkulator.mainApp.actionPerformed(mainApp.java:299)
at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
at javax.swing.AbstractButton.doClick(Unknown Source)
at javax.swing.plaf.basic.BasicMenuItemUI.doClick(Unknown Source)
at javax.swing.plaf.basic.BasicMenuItemUI$Handler.mouseReleased(Unknown Source)
at java.awt.Component.processMouseEvent(Unknown Source)
at javax.swing.JComponent.processMouseEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$200(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)

下面是我修改后用于我的应用程序的示例：

 package calc.kalkulator;

import javax.swing.JPanel;

import org.jfree.chart.ChartFactory;
import org.jfree.chart.ChartPanel;
import org.jfree.chart.JFreeChart;
import org.jfree.chart.plot.PlotOrientation;
import org.jfree.chart.plot.XYPlot;
import org.jfree.data.function.Function2D;
import org.jfree.data.general.DatasetUtilities;
import org.jfree.data.xy.XYDataset;
import org.jfree.ui.ApplicationFrame;

class OknoFunkcji extends ApplicationFrame {

private static PanelFunkcji panelFunkcji;
private static double a;
private static double b;
private static double c;
private static double d;

public void getDane () {
    a = panelFunkcji.getA();
    b = panelFunkcji.getB();
    c = panelFunkcji.getC();
    d = panelFunkcji.getD();
}


public OknoFunkcji(String title) {
    super(title);
    JPanel chartPanel = createDemoPanel();
    //chartPanel.setPreferredSize(new java.awt.Dimension(500, 270));
    chartPanel.setSize(500, 270);
    setContentPane(chartPanel);
    getDane();




}

/**
 * Tworzy chart.
 * 
 * @param dataset - zbiór danych.
 * 
 * @return Zwraca instancję charta.
 */
private static JFreeChart createChart(XYDataset dataset) {
    // create the chart...
    JFreeChart chart = ChartFactory.createXYLineChart(
        " ",       // chart title
        "X",                      // x axis label
        "Y",                      // y axis label
        dataset,                  // data
        PlotOrientation.VERTICAL,  
        true,                     // include legend
        true,                     // tooltips
        false                     // urls
    );

    XYPlot plot = (XYPlot) chart.getPlot();
    plot.getDomainAxis().setLowerMargin(0.0);
    plot.getDomainAxis().setUpperMargin(0.0);
    return chart;
}

/**
 * Creates a sample dataset.
 * 
 * @return A sample dataset.
 */
public static XYDataset createDataset() {
    XYDataset result = DatasetUtilities.sampleFunction2D(new X2(), 
            -10.0, 10.0, 40, "f(x)");
    return result;
}

public static JPanel createDemoPanel() {
    JFreeChart chart = createChart(createDataset());
    return new ChartPanel(chart);
}

static class X2 implements Function2D {

    public double getValue(double x) {
        return a*x*x*x + b*x*x + c*x + d;
    }

}



}

---

出于某种奇怪的原因，无论我做什么，我都会得到NullPointerException

错误在以下代码中：

private static PanelFunkcji panelFunkcji;   //1
private static double a;
private static double b;
private static double c;
private static double d;

public void getDane()
{
    a = panelFunkcji.getA();   //9
    b = panelFunkcji.getB();
    c = panelFunkcji.getC();
    d = panelFunkcji.getD();
}

public OknoFunkcji(String title)
{
    super(title);
    JPanel chartPanel = createDemoPanel();
    //chartPanel.setPreferredSize(new java.awt.Dimension(500, 270));
    chartPanel.setSize(500, 270);
    setContentPane(chartPanel);
    getDane();    //22
}

在第1行声明变量

panelFunkcji

，并在第9行使用它。但是，您从未实例化该变量。这就是导致

NullPointerException

的原因

要修复它，请添加行

panelFunkcji = new PanelFunkcji(chartPanel);

---

第22行之前的

OknoFunkcji

构造函数中的任何位置。

哪一行是NullPointerException？感谢您的回答。但是，在这样做之后：

public-OknoFunkcji（字符串标题）{super（标题）；JPanel-chartPanel=createDemoPanel（）；panelFunkcji=new-panelFunkcji（chartPanel）；chartPanel.setSize（500270）；setContentPane（chartPanel）；getDane（）；}

我得到

构造函数面板funkcji（JPanel）未定义的
错误。我该如何解决这个问题？我知道我必须为它制作构造器，但我确实是Java Swing和Java的新手，我非常感谢您的帮助。@Asunez抱歉，这是我没有注意到的错误。应该使用构造函数
PanelFunkcji（JFrame）
。因此，在
panelFunkcji=newpanelfunkcji（chartpanel）行中，不使用
chartpanel
，您应该将
JFrame
对象作为参数。我对秋千了解不多，所以我帮不了你。谢谢！现在它编译时没有任何错误，但是，在将所有a、b、c和d变量打印到控制台后，它们都设置为0。我认真地看了几个小时的代码，几乎熟记在心，但仍然不知道，为什么我不能将这些数据转发到另一个窗口。。。请告诉我你还有其他想法。。。
panelFunkcji = new PanelFunkcji(chartPanel);