java - 如何制作一个猜数字游戏

Question

我需要制作一个猜谜游戏程序。我想不出任何方法可以成功记录两个猜测以进行比较。我对“actionPerformed”方法遇到的问题最多。它没有链接到构造函数 - 就像 txtFld 和 Lbl3 一样，它表示它是一个空指针。这是我到目前为止所拥有的:

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


public class GuessTheNumber extends JFrame
{
    Random randNum = new Random();
    int numToGuess = randNum.nextInt(1000);
    int guess1;
    int guess2;

    public static void main(String [] args)
    {
        new GuessTheNumber();

    } // end main

    public GuessTheNumber()
    {
        setTitle("Guess The Number");
        setLayout(new FlowLayout());

        JLabel promptLbl1 = new JLabel("I have a number between 1 and 1000.  Can you guess my number?");
        add(promptLbl1);
        JLabel promptLbl2 = new JLabel("Please enter your guess.");
        add(promptLbl2);
        JTextField txtFld = new JTextField(4);
        add(txtFld);
        JLabel Lbl3 = new JLabel();
        add(Lbl3);
        MyHandler handler = new MyHandler();
        txtFld.addActionListener(handler);
        setSize(300,300);
        setVisible(true);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    }  //end constructor

    private class MyHandler implements ActionListener
    {
        public void actionPerformed(ActionEvent ev)
        {
            String gs1;
            guess1 = txtFld.getText();  
            guess1 = Integer.parseInt(gs1);
            String gs2;
            guess2 = txtFld.getText();  
            guess2 = Integer.parseInt(gs2);

            if (gs1 > gs2)
                txtFld.setBackground(color.blue);

            else if (gs1 < gs2)
                txtFld.setBackground(color.red);

            if (gs2 == numToGuess)  
            {
                Lbl3("Correct!"); 
                txtFld.setBackground(color.green);
            }

            else if (gs2 > numToGuess)
                Lbl3("Too High");

            else if (gs2 < numToGuess)
                Lbl3("Too Low");

        } // end actionPerformed  

    } // end MyHandler

} // end GuessTheNumber

Answer 1

您必须将标签和文本字段的声明从构造函数移动到 GuessTheNumber。

public class GuessTheNumber extends JFrame
{
Random randNum = new Random();
int numToGuess = randNum.nextInt(1000);
int guess1;
int guess2;

JLabel promptLbl1;
JLabel promptLbl2;
JTextField txtFld;
JLabel Lbl3;
//...


public GuessTheNumber()
{
    setTitle("Guess The Number");
    setLayout(new FlowLayout());

    promptLbl1 = new JLabel("I have a number between 1 and 1000.  Can you guess my number?");
    add(promptLbl1);
    promptLbl2 = new JLabel("Please enter your guess.");
    add(promptLbl2);
    txtFld = new JTextField(4);
    add(txtFld);
    Lbl3 = new JLabel();
    add(Lbl3);
    //...

否则您只能在构造函数中访问它们。