java - 是什么原因导致 "Can' t find Symbol”以及如何解决？

Question

我一直在努力解决这个问题，我在不同的程序中运行过它，所以它肯定在代码中。可能也很容易。错误说

Password2.java:90: error: cannot find symbol if(pw.equals(password)) ^ symbol: variable password location: class Password2.EnterButtonHandler 1 error

代码如下:

// Password1.java

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

public class Password2 extends JFrame // inherits from the JFrame class 
{
    // static final variables to hold frame dimensions (in pixels) 
    private static final int WIDTH = 400;
    private static final int HEIGHT = 120;

    //declare labels, fields, buttons, etc.
    private JLabel enterLabel, validLabel, resultLabel;
    private JTextField pwTextField;
    private JButton enterB, clearB;

    private EnterButtonHandler ebHandler;
    private ClearButtonHandler cbHandler;

    public Password2() // constructor defines frame 
    { 
            setTitle( "Password Checker" ); // set the title of the frame
        setSize( WIDTH, HEIGHT ); // set the frame size

        // prepare the container 
        Container pane = getContentPane();
        GridLayout aGrid = new GridLayout( 3, 2, 5, 5 ); // create a 3 row 2 column layout
        pane.setLayout( aGrid ); // set the layout for the frame

        String password = "hello";

        //instantiate JLabels
        enterLabel = new JLabel("Enter Password: ");
        validLabel = new JLabel("Validation: ");
        resultLabel = new JLabel("");

        //instantiate text fields
        pwTextField = new JPasswordField( 30 );

        //instantiate buttons
        enterB = new JButton("Enter");
        clearB = new JButton("Clear");

        //initialize button handler
        ebHandler = new EnterButtonHandler();
        enterB.addActionListener(ebHandler);

        //initialize button handler
        cbHandler = new ClearButtonHandler();
        clearB.addActionListener(cbHandler);


        pane.add(enterLabel);
        pane.add(pwTextField);
        pane.add(validLabel);
        pane.add(resultLabel);
        pane.add(enterB);
        pane.add(clearB);

        //calls center frame method
        centerFrame( WIDTH, HEIGHT );

    }// end constructor

    //methood to center GUI on screen
    public void centerFrame( int frameWidth, int frameHeight)
    {
        //create toolkit object
        Toolkit aToolkit = Toolkit.getDefaultToolkit();

        //create a dimension object with user screen information
        Dimension screen = aToolkit.getScreenSize();

        //assign x, y position of upper left corner of frame
        int xUpperLeft = ( screen.width - frameWidth ) / 2;
        int yUpperLeft = ( screen.height - frameHeight ) / 2;

        //method to position frame on user's screen
        setBounds( xUpperLeft, yUpperLeft, frameWidth, frameHeight );
    }

    private class EnterButtonHandler implements ActionListener
    {
        public void actionPerformed(ActionEvent e)
        {
            String pw = pwTextField.getText();

            if(pw.equals(password))
            {
                resultLabel.setText("Password Accepted");
                pwTextField.setText("");
            }
            else
            {
                resultLabel.setText("Password Rejected");
                pwTextField.setText("");
            }
        }
    }
    private class ClearButtonHandler implements ActionListener
    {
        public void actionPerformed(ActionEvent e)
        {
            resultLabel.setText("");
            pwTextField.setText("");
        }

    }
    public static void main(String [] args) 
    {
        JFrame aPassword2 = new Password2(); // create the JFrame object
        aPassword2.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        aPassword2.setVisible(true);
    }
    } // end of class

Answer 1

阅读错误信息，喜欢错误信息。

这需要一些练习，但一段时间后很容易看得更清楚:只需阅读下面的粗体文本作为句子:)

error: cannot find symbol [...]

symbol: variable password

location: [in] class Password2.EnterButtonHandler

password在该作用域/上下文中 (EnterButtonHandler)。

快乐编码。

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提示:在不同范围/上下文中有一个具有相同名称的本地变量...也许它不应该是本地变量？参见 The Java Tutorial: Variables更多 :)