空按钮监听器

时间：2013-12-09 03:30:05

标签： java user-interface

我现在只使用Java大约一年了，刚刚学习了GUI的基础知识。我正在编写一个计算2,3,4或5点之间质量中心的程序（用户选项）。根据用户想要输入的点数，一些可编辑的JTextField似乎可以获得坐标和这些坐标质量的输入。不幸的是，当被要求计算质心时，按钮将不会显示我想要的内容。它现在编写的方式是我编译/运行没有空字符串错误的唯一方法。我相信它与我如何初始化变量/它们在构造函数之间初始化的位置有关，但我不能在我的生活中弄清楚问题究竟在哪里。任何帮助将不胜感激！我附上了代码 - 我知道它很长，但你永远不知道什么是有用的。谢谢！

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.util.*;

public class ComboBox extends JFrame
/*************VARIABLES*******************************************************/
{
   private final int WIDTH = 1500;
   private final int HEIGHT = 1500;
   private JPanel northPanel;
   private JPanel centerPanel;

private JPanel blankPanel;
private JPanel pointsPanel;
private JPanel selectedPointsPanel;
private JComboBox pointsBox;
private JTextField selectedPoints;
private JLabel selection;
private String choose = "Choose an option...";
private String twoPoints = "2 points";
private String threePoints = "3 points";
private String fourPoints = "4 points";
private String fivePoints = "5 points";
private String[] points = {choose, twoPoints, threePoints, fourPoints, fivePoints};

private JPanel coordinatesPanel;
private JPanel cPanel;
private JTextField xField1; 
private JTextField xField2;
private JTextField xField3;
private JTextField xField4;
private JTextField xField5;
private JTextField yField1;
private JTextField yField2;
private JTextField yField3;
private JTextField yField4;
private JTextField yField5;
private JLabel instructions; 
private JLabel X;
private JLabel Y;
private JLabel blankLabel; 

private JPanel massPanel;
private JTextField mass1 = new JTextField(10);
private JTextField mass2 = new JTextField(10);
private JTextField mass3 = new JTextField(10);
private JTextField mass4 = new JTextField(10);
private JTextField mass5 = new JTextField(10);
private JLabel instructions2;

Boolean calcBool = false;
private JButton calcButton = new JButton("Calculate");
private JButton resetButton = new JButton("Reset");

private JPanel displayPanel;
private double centerX;
private double centerY;
private JLabel display; 

private double x1, x2, x3, x4, x5;
private double y1, y2, y3, y4, y5;
private double m1, m2, m3, m4, m5;


/**********************************WINDOW************************************/  
public ComboBox()
{
  super("Choose an option");
  setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  setLayout(new GridLayout(3,2));
  setLocationRelativeTo(null);
  setResizable(true);
  setSize(WIDTH, HEIGHT);

  buildPointsPanel();
  buildCoordinatesPanel();
  buildMassPanel();
  buildDisplayPanel();
  buildBlankPanel();

  add(pointsPanel);
  add(coordinatesPanel);
  add(massPanel);
  add(blankPanel);
  add(calcButton);
  add(blankPanel);
  add(resetButton);
  add(blankPanel);
  add(displayPanel);

  calcButton.addActionListener(new CalcButtonListener());
  pointsBox.addActionListener(new ComboBoxListener());
  //resetButton.addActionListener(new ResetButtonListener());

  pack();
  setVisible(true);

} 

/************************BUILD ALL THE PANELS**********************/
private void buildBlankPanel()
{
  blankPanel = new JPanel();
}
private void buildPointsPanel()
{
  pointsPanel = new JPanel();
     pointsPanel.setLayout(new GridLayout(3,1));
  pointsBox = new JComboBox(points);
  pointsBox.addActionListener(new ComboBoxListener());
  pointsPanel.add(pointsBox);
  selection = new JLabel("You selected: ");
  selectedPoints = new JTextField(10);
  selectedPoints.setEditable(false);
  pointsPanel.add(selection);
  pointsPanel.add(selectedPoints);
}

private void buildCoordinatesPanel()
{
  coordinatesPanel = new JPanel();
  coordinatesPanel.setLayout(new GridLayout(6,2));
  instructions = new JLabel("Please enter the X and Y values of your points below.");
  JLabel blank = new JLabel("");
  X = new JLabel("X values");
  Y = new JLabel("Y values");
  blankLabel = new JLabel("");

  coordinatesPanel.add(instructions);
  coordinatesPanel.add(blankLabel);
  coordinatesPanel.add(X);
  coordinatesPanel.add(Y);

  xField1 = new JTextField(10);
     xField1.setEditable(true);
  yField1 = new JTextField(10);
   yField1.setEditable(true);
  xField2 = new JTextField(10);
     xField2.setEditable(true);
  yField2 = new JTextField(10);
     yField2.setEditable(true);
  xField3 = new JTextField(10);
   xField3.setEditable(true);
  yField3 = new JTextField(10);
   yField3.setEditable(true);
  xField4 = new JTextField(10);
   xField4.setEditable(true);
  yField4 = new JTextField(10);
   yField4.setEditable(true);
  xField5 = new JTextField(10);
   xField5.setEditable(true);
  yField5 = new JTextField(10);
   yField5.setEditable(true);
}

private void buildMassPanel()
{
  massPanel = new JPanel();
  instructions2 = new JLabel("Please enter the masses of your points");
  massPanel.add(instructions2);
  mass1.setEditable(true);
  mass2.setEditable(true);
  mass3.setEditable(true);
  mass4.setEditable(true);
  mass5.setEditable(true);
}

private void buildDisplayPanel()
{
   displayPanel = new JPanel();
  //display = new JLabel("The center of mass is located at (" + centerX + "," + centerY
  +").");
  //displayPanel.add(display);
 }

/********************************COMBOBOX LISTENER****************************/     
private class ComboBoxListener implements ActionListener
{
  public void actionPerformed(ActionEvent e)
  { //The following asks the user to select the number of points they want and stores
       it
     String select =(String) pointsBox.getSelectedItem();
     selectedPoints.setText(select);

  //The following determines how many text fields to display depending on how many     
    points the user wants

     if (select==twoPoints)
     {
        coordinatesPanel.add(xField1);
        coordinatesPanel.add(yField1);
        coordinatesPanel.add(xField2);
        coordinatesPanel.add(yField2);

        massPanel.add(mass1);
        massPanel.add(mass2);

centerX = ((m1*x1)+(m2*x2)/(m1+m2));
        centerY = ((m1*y1)+(m2*y2)/(m1+m2));
      }
     if (select==threePoints)
     {
        coordinatesPanel.add(xField1);
        coordinatesPanel.add(yField1);
        coordinatesPanel.add(xField2);
        coordinatesPanel.add(yField2);
        coordinatesPanel.add(xField3);
        coordinatesPanel.add(yField3);

        massPanel.add(mass1);
        massPanel.add(mass2);
        massPanel.add(mass3);

    centerX = ((m1*x1)+(m2*x2)+(m3*x3)/(m1+m2+m3));
        centerY = ((m1*y1)+(m2*y2)+(m3*y3)/(m1+m2+m3));
     }
     if (select==fourPoints)
     {
        coordinatesPanel.add(xField1);
        coordinatesPanel.add(yField1);
        coordinatesPanel.add(xField2);
        coordinatesPanel.add(yField2);
        coordinatesPanel.add(xField3);
        coordinatesPanel.add(yField3);
        coordinatesPanel.add(xField4);
        coordinatesPanel.add(yField4);

        massPanel.add(mass1);
        massPanel.add(mass2);
        massPanel.add(mass3);
        massPanel.add(mass4);

    centerX = ((m1*x1)+(m2*x2)+(m3*x3)+(m4*x4)/(m1+m2+m3+m4));
        centerY = ((m1*y1)+(m2*y2)+(m3*y3)+(m4*y4)/(m1+m2+m3+m4));
        }
     if (select==fivePoints)
     {
        coordinatesPanel.add(xField1);
        coordinatesPanel.add(yField1);
        coordinatesPanel.add(xField2);
        coordinatesPanel.add(yField2);
        coordinatesPanel.add(xField3);
        coordinatesPanel.add(yField3);
        coordinatesPanel.add(xField4);
        coordinatesPanel.add(yField4);
        coordinatesPanel.add(xField5);
        coordinatesPanel.add(yField5);

        massPanel.add(mass1);
        massPanel.add(mass2);
        massPanel.add(mass3);
        massPanel.add(mass4);
        massPanel.add(mass5);

    centerX = ((m1*x1)+(m2*x2)+(m3*x3)+(m4*x4)+(m5*x5)/(m1+m2+m3+m4+m5));
        centerY = ((m1*y1)+(m2*y2)+(m3*y3)+(m4*y4)+(m5*y5)/(m1+m2+m3+m4+m5));
     }
     if (select==choose)
     {
        JOptionPane.showMessageDialog(null, "Please select a valid option");
     }
  }
}
/********************************CALC BUTTON LISTENER******************************/   
private class CalcButtonListener implements ActionListener
{
  public void actionPerformed(ActionEvent e)
  {
    display = new JLabel("The center of mass is located at (" + centerX + "," + centerY
     +").");
displayPanel.add(display);
  }       

}
/******************************MAIN METHOD***************************/      
public static void main(String[] args)
{
  new ComboBox();
}

2 个答案:

答案 0 :(得分：0)

你应该做的是实例化你声明它的display。 

JLabel display = new JLabel("  ");

然后将其添加到GUI，无论您在代码中添加所有其他组件。比在你的监听器类中，只需设置文本

public void actionPerformed(ActionEvent e){
    display.setText("some text");
}

你这样做的方式可能搞乱你想要的GUI格式。但是，如果您这样做，则在添加任何新组件后，您需要revalidate()和repaint()。我建议使用前者。

答案 1 :(得分：0)

不知道你的具体问题在哪里，但看看你的代码，我发现了一些潜在的错误。在java中，您将对象与equals()和==进行比较。==仅供参考。

因此，将用字符串==与equals进行比较的所有行都更改为select==fivePoints。

例如更改

select.equals(fivePoints) 到

private JTextField mass1 = new JTextField(10);
private JTextField mass2 = new JTextField(10);
private JTextField mass3 = new JTextField(10);
private JTextField mass4 = new JTextField(10);
private JTextField mass5 = new JTextField(10);

拥有像

这样的属性 
Collection

不是最佳方式，您可以将它们存储在private List<JTextField> masses; 或数组中。 

revalidate

始终在添加组件调用repaint和 display = new JLabel("The center of mass is located at (" + centerX + "," + centerY +")."); displayPanel.add(display); displayPanel.revalidate(); displayPanel.repaint(); 时。 

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