JTextField不工作，因为它应该

Question

我想做一个简单的计算器使用Java。下面是用于创建GUI的代码。

import java.awt.*; 
import java.awt.event.ActionEvent; 
import java.awt.event.ActionListener; 
import javax.swing.*; 

public class Calculator extends JFrame implements ActionListener { 

    private JButton one, two, three, four, five, six, seven, eight, nine, zero, plus, minus, 
      multiply, divide, equalTo, point; 
    private JPanel panelForResult, panelForKeys; 
    private JLabel Result; 
    private JTextField result; 

    public Calculator() { 
    } 

    @Override 
    public void actionPerformed(ActionEvent ae) { 
    } 

    public static void main(String... args) { 


     Calculator calcFrame = new Calculator(); 
     calcFrame.setSize(330, 400); 
     calcFrame.setVisible(true); 
     calcFrame.setResizable(false); 
     calcFrame.createCalcGUI(); 

    } 

    private void createCalcGUI() { 
     setDefaultCloseOperation(EXIT_ON_CLOSE); 



     Container window = getContentPane(); 
     window.setBackground(Color.blue); 
     window.setSize(400, 400); 

     FlowLayout windowLayout = new FlowLayout(); 
     windowLayout.setHgap(50); 
     window.setLayout(windowLayout); 


     panelForKeys = new JPanel(); 
     panelForKeys.setBackground(Color.CYAN); 
     panelForKeys.setPreferredSize(new Dimension(200, 250)); 

     FlowLayout buttonLayout = new FlowLayout(); 
     // buttonLayout.setAlignOnBaseline(true); 
     panelForKeys.setLayout(buttonLayout); 

     panelForResult = new JPanel(); 
     panelForResult.setBackground(Color.CYAN); 
     panelForResult.setPreferredSize(new Dimension(200, 50)); 
     panelForResult.setLayout(new FlowLayout()); 


     Result = new JLabel("="); 
     result = new JTextField(); 

     one = new JButton("1"); 
     two = new JButton("2"); 
     three = new JButton("3"); 
     four = new JButton("4"); 
     five = new JButton("5"); 
     six = new JButton("6"); 
     seven = new JButton("7"); 
     eight = new JButton("8"); 
     nine = new JButton("9"); 
     zero = new JButton("0"); 
     plus = new JButton("+"); 
     minus = new JButton("-"); 
     multiply = new JButton("*"); 
     divide = new JButton("÷"); 
     equalTo = new JButton("="); 
     point = new JButton(". "); 




     one.addActionListener(this); 
     two.addActionListener(this); 
     three.addActionListener(this); 
     four.addActionListener(this); 
     five.addActionListener(this); 
     six.addActionListener(this); 
     seven.addActionListener(this); 
     eight.addActionListener(this); 
     nine.addActionListener(this); 
     zero.addActionListener(this); 
     plus.addActionListener(this); 
     minus.addActionListener(this); 
     divide.addActionListener(this); 
     multiply.addActionListener(this); 
     equalTo.addActionListener(this); 
     point.addActionListener(this); 

     panelForKeys.add(one); 
     panelForKeys.add(two); 
     panelForKeys.add(three); 
     panelForKeys.add(four); 
     panelForKeys.add(five); 
     panelForKeys.add(six); 
     panelForKeys.add(seven); 
     panelForKeys.add(eight); 
     panelForKeys.add(nine); 
     panelForKeys.add(zero); 
     panelForKeys.add(minus); 
     panelForKeys.add(plus); 
     panelForKeys.add(multiply); 
     panelForKeys.add(divide); 
     panelForKeys.add(equalTo); 
     panelForKeys.add(point); 


     window.add(panelForResult); 
     window.add(this.panelForKeys); 

     panelForResult.add(Result); 
     panelForResult.add(result); 


    } 
} 

每当我创建的JTextField的实例，并在panelForResult添加它的整个容器窗口得到蓝色。如果我评论JTextField然后它的作品。我只是Java的初学者，我可能知道可能的原因以及如何纠正它？

Answer 1

这很可能是因为您在主线程上制作GUI而不是Event Dispatch Thread。

只能在事件调度线程上访问Swing组件。这可以通过呼叫SwingUtilities.invokeLater来实现。

在你的情况，你的主要方法改成这样：

public static void main(String... args) { 
    SwingUtilities.invokeLater(new Runnable() { 
     @Override 
     public void run() { 
      Calculator calcFrame = new Calculator(); 
      calcFrame.setSize(330, 400); 
      calcFrame.setVisible(true); 
      calcFrame.setResizable(false); 
      calcFrame.createCalcGUI(); 
     } 
    }); 
} 

编辑： 在Java中，有一些所谓的线程。通过使用多个线程，您可以同时运行多个代码段，这可以提高效率。

但是，并不是所有的代码可以同时安全地在不同的线程上运行。例如，Swing组件。 Swing组件只能在称为Event Dispatch Thread的特定线程上访问。

您可以阅读更多关于线程here。

Answer 2

您的代码有几个问题，很难提供确切的答案。这里有几件事情上下工夫：

• JFrame.setVisible(true)应该是你最后一次通话（设置UI调用它之前，还是请确保调用pack()之后）
• 不要强迫preferredSize（不曾经呼吁setPreferredSize）。这可能是你的问题的原因。始终使用适当的LayoutManager。
• 不要依靠FlowLayout来执行组件换行。
• 做它用SwingUtilities.invokeLater()

这里是你的代码的工作示例（不知道通过设置列

上调用EDT所有Swing相关的代码（数量提供一个尺寸暗示的JTextField虽然它符合布局你的想法）：

import java.awt.Color; 
import java.awt.Container; 
import java.awt.FlowLayout; 
import java.awt.GridLayout; 
import java.awt.event.ActionEvent; 
import java.awt.event.ActionListener; 

import javax.swing.BoxLayout; 
import javax.swing.JButton; 
import javax.swing.JFrame; 
import javax.swing.JLabel; 
import javax.swing.JPanel; 
import javax.swing.JTextField; 
import javax.swing.SwingUtilities; 

public class Calculator extends JFrame implements ActionListener { 

    private JButton one, two, three, four, five, six, seven, eight, nine, zero, plus, minus, multiply, divide, equalTo, point; 
    private JPanel panelForResult, panelForKeys; 
    private JLabel Result; 
    private JTextField result; 

    public Calculator() { 
    } 

    @Override 
    public void actionPerformed(ActionEvent ae) { 
    } 

    public static void main(String... args) { 
     SwingUtilities.invokeLater(new Runnable() { 
      @Override 
      public void run() { 
       Calculator calcFrame = new Calculator(); 
       calcFrame.createCalcGUI(); 
       calcFrame.setResizable(false); 
       calcFrame.pack(); 
       calcFrame.setVisible(true); 
      } 
     }); 

    } 

    private void createCalcGUI() { 
     setDefaultCloseOperation(EXIT_ON_CLOSE); 

     Container window = getContentPane(); 
     window.setBackground(Color.blue); 

     BoxLayout windowLayout = new BoxLayout(window, BoxLayout.PAGE_AXIS); 
     window.setLayout(windowLayout); 

     panelForKeys = new JPanel(new GridLayout(0, 3, 5, 5)); 
     panelForKeys.setBackground(Color.CYAN); 

     panelForResult = new JPanel(); 
     panelForResult.setBackground(Color.CYAN); 
     panelForResult.setLayout(new FlowLayout()); 

     Result = new JLabel("="); 
     result = new JTextField(12); 

     one = new JButton("1"); 
     two = new JButton("2"); 
     three = new JButton("3"); 
     four = new JButton("4"); 
     five = new JButton("5"); 
     six = new JButton("6"); 
     seven = new JButton("7"); 
     eight = new JButton("8"); 
     nine = new JButton("9"); 
     zero = new JButton("0"); 
     plus = new JButton("+"); 
     minus = new JButton("-"); 
     multiply = new JButton("*"); 
     divide = new JButton("÷"); 
     equalTo = new JButton("="); 
     point = new JButton(". "); 

     one.addActionListener(this); 
     two.addActionListener(this); 
     three.addActionListener(this); 
     four.addActionListener(this); 
     five.addActionListener(this); 
     six.addActionListener(this); 
     seven.addActionListener(this); 
     eight.addActionListener(this); 
     nine.addActionListener(this); 
     zero.addActionListener(this); 
     plus.addActionListener(this); 
     minus.addActionListener(this); 
     divide.addActionListener(this); 
     multiply.addActionListener(this); 
     equalTo.addActionListener(this); 
     point.addActionListener(this); 

     panelForKeys.add(one); 
     panelForKeys.add(two); 
     panelForKeys.add(three); 
     panelForKeys.add(four); 
     panelForKeys.add(five); 
     panelForKeys.add(six); 
     panelForKeys.add(seven); 
     panelForKeys.add(eight); 
     panelForKeys.add(nine); 
     panelForKeys.add(zero); 
     panelForKeys.add(minus); 
     panelForKeys.add(plus); 
     panelForKeys.add(multiply); 
     panelForKeys.add(divide); 
     panelForKeys.add(equalTo); 
     panelForKeys.add(point); 

     window.add(panelForResult); 
     window.add(this.panelForKeys); 

     panelForResult.add(Result); 
     panelForResult.add(result); 

    } 
}