java - 静态和非静态问题

Question

我是 Java 的新手，现在正在学习初学者类(class)。非常好，我正在尝试各种方法，但现在我被卡住了。这段代码不起作用。它应该以相反的顺序(按单词)输出输入。

翻转它的代码在我编写的没有 GUI 的一段代码中工作，现在我试图让它在具有固定按钮、标签等的 GUI 中工作。为此，我从互联网上复制了一个例子，并试图以这样的方式改变它。但它似乎没有找到我在 actionPerformed 中使用并在 AddComponentsToPane 中设置的变量。它必须对静态和非静态做一些事情，我似乎不太清楚

任何帮助将不胜感激。

这是代码。

package flipit;


import java.applet.Applet;
import java.awt.*;
import java.awt.event.*;
import java.util.List;
import java.util.*; //ArrayList;
import javax.swing.*;

public class FlipIt extends JFrame implements ActionListener {

public static void addComponentsToPane(Container pane) {

  pane.setLayout(null);

  JLabel     greetingLabel   = new JLabel("Enter your array ");
  JTextField inField         = new JTextField();
  JTextField commentaryField = new JTextField();
  JTextField strLen          = new JTextField();
  JButton    button          = new JButton("FlipIt");

  pane.add(greetingLabel);
  pane.add(inField);
  pane.add(commentaryField);
  pane.add(button);        

  Insets insets  = pane.getInsets();
  Dimension size = button.getPreferredSize();

  greetingLabel.setBounds (   5 + insets.left, 35 + insets.top,size.width + 40, size.height);
  inField.setBounds        (120 + insets.left, 33 + insets.top,size.width + 200, size.height);
  //size = commentaryField.getPreferredSize();
  commentaryField.setBounds(120 + insets.left, 80 + insets.top,size.width + 200, size.height);
  size = button.getPreferredSize();
  button.setBounds         (  5 + insets.left, 80 + insets.top,size.width + 40, size.height);

}

private static void createAndShowGUI() {
    //Create and set up the window.

    JFrame frame = new JFrame("Reverse the input string.");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    //Set up the content pane.
    addComponentsToPane(frame.getContentPane());

    //Size and display the window.
    Insets insets = frame.getInsets();
    frame.setSize(500 + insets.left + insets.right,
                  425 + insets.top + insets.bottom);
    frame.setVisible(true);
}

    public static void main(String[] args) {
     Scanner input = new Scanner(System.in);

    //Schedule a job for the event-dispatching thread:
    //creating and showing this application's GUI.
    javax.swing.SwingUtilities.invokeLater(new Runnable() {
        public void run() {
            createAndShowGUI();
        }
    });
}

public void actionPerformed(ActionEvent event) {

    String InputStr = inField.getText();
    int length = InputStr.length(); 

    if (InputStr.compareTo("") == 0 || InputStr == null) {
        commentaryField.setText("Please enter some data, this array is empty");
    }
    else {

        // Convert string variable to an ArrayList.
        List<String> list = new ArrayList<String>(Arrays.asList(InputStr.split(" ")));            
        // Converting ArrayList to a String Array
        String [] InputList = list.toArray(new String[list.size()]);

        int i = 0 ;
        String ReverseOrder = "" ;

        // starting for loop to print the array in reversed order.
        for (i=InputList.length-1;i>=0; i--)
            {ReverseOrder = ReverseOrder + " " + InputList[i] ;
           }
        // print result.
          commentaryField.setText(ReverseOrder);   
          strLen.setText("Lengte string : "+ length);  
     }
   }  
}

谢谢，罗布。

Answer 1

主要问题是范围界定问题。由于您是在addComponentsToPane 方法内部声明小部件，因此从方法外部看不到它们。

尝试将小部件声明移到 addComponentstoPane 方法之外:

JLabel     greetingLabel   = new JLabel("Enter your array ");
JTextField inField         = new JTextField();
JTextField commentaryField = new JTextField();
JTextField strLen          = new JTextField();
JButton    button          = new JButton("FlipIt");

public static void addComponentsToPane(Container pane) {

  pane.setLayout(null);

  pane.add(greetingLabel);
  pane.add(inField);
  pane.add(commentaryField);
  pane.add(button);     
  // etc
}

正如您所指出的(抱歉，我的错!)您的静态方法将无法再访问小部件(因为它们现在是类实例 的一部分)。

考虑静态与非静态的简单方法是，如果您将某物声明为静态，则不需要需要类实例来访问它。因此在您的代码中为什么可以这样做:

public void run() {
    createAndShowGUI();
}

实际上，这与这样做是一样的:

public void run() {
    FlipIt.createAndShowGUI();
}

请注意，您还没有创建 FlipIt 类的实例；您不需要，因为 createAndShowGUI 方法是 static。但是，如果它不是是静态的，那么您将不得不创建一个新的类实例，如下所示:

public void createAndShowGUI() {
    // do your thing - note NO LONGER STATIC
}

public void run() {
    // Create instance
    FlipIt flipper = new FlipIt();

    // Invoke method against class instance
    flipper.createAndShowGUI();
}

所以 - 为了让您的代码正常工作，最好的解决方案是使所有内容都非静态(当然 main 方法除外，它必须是静态的).

这是全部放在一起的整个代码示例 - 请注意，您可能需要将 createAndShowGUI 方法设为 public - 但我不这么认为。我已经有一段时间没有用 Java 编写代码了，所以我不能确定。

package flipit;


import java.applet.Applet;
import java.awt.*;
import java.awt.event.*;
import java.util.List;
import java.util.*; //ArrayList;
import javax.swing.*;

public class FlipIt extends JFrame implements ActionListener {
  JLabel     greetingLabel   = new JLabel("Enter your array ");
  JTextField inField         = new JTextField();
  JTextField commentaryField = new JTextField();
  JTextField strLen          = new JTextField();
  JButton    button          = new JButton("FlipIt");

  public void addComponentsToPane(Container pane) {
    pane.setLayout(null);

    pane.add(greetingLabel);
    pane.add(inField);
    pane.add(commentaryField);
    pane.add(button);        

    Insets insets  = pane.getInsets();
    Dimension size = button.getPreferredSize();

    greetingLabel.setBounds (   5 + insets.left, 35 + insets.top,size.width + 40, size.height);
    inField.setBounds        (120 + insets.left, 33 + insets.top,size.width + 200, size.height);
    //size = commentaryField.getPreferredSize();
    commentaryField.setBounds(120 + insets.left, 80 + insets.top,size.width + 200, size.height);
    size = button.getPreferredSize();
    button.setBounds         (  5 + insets.left, 80 + insets.top,size.width + 40, size.height);
  }

  private void createAndShowGUI() {
    //Create and set up the window.
    JFrame frame = new JFrame("Reverse the input string.");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    //Set up the content pane.
    addComponentsToPane(frame.getContentPane());

    //Size and display the window.
    Insets insets = frame.getInsets();
    frame.setSize(500 + insets.left + insets.right,
                  425 + insets.top + insets.bottom);
    frame.setVisible(true);
  }

  public void actionPerformed(ActionEvent event) {
    String InputStr = inField.getText();
    int length = InputStr.length(); 

    if (InputStr.compareTo("") == 0 || InputStr == null) {
      commentaryField.setText("Please enter some data, this array is empty");

    } else {

      // Convert string variable to an ArrayList.
      List<String> list = new ArrayList<String>(Arrays.asList(InputStr.split(" ")));            
      // Converting ArrayList to a String Array
      String [] InputList = list.toArray(new String[list.size()]);

      int i = 0 ;
      String ReverseOrder = "" ;

      // starting for loop to print the array in reversed order.
      for (i=InputList.length-1;i>=0; i--) {
        ReverseOrder = ReverseOrder + " " + InputList[i] ;
      }

      // print result.
      commentaryField.setText(ReverseOrder);   
      strLen.setText("Lengte string : "+ length);  
    }
  }  

  public static void main(String[] args) {
      Scanner input = new Scanner(System.in);

      //Schedule a job for the event-dispatching thread:
      //creating and showing this application's GUI.
      javax.swing.SwingUtilities.invokeLater(new Runnable() {
        public void run() {
          FlipIt flipper = new FlipIt();
          flipper.createAndShowGUI();
        }
      });
    }
  }
}

希望对您有所帮助!