java - StringIndexOutOfBoundsException 的问题

Question

我必须创建一个数字内存游戏，但如果用户输入错误的数字，我会收到 StringIndexOutOfBoundsException。我看了很多例子，但仍然不知道如何解决它。这发生在 actionPerformed 方法中，使用这行代码 newNumber = answer.substring(counterOne, counterTwo); 任何帮助将不胜感激。

import java.applet.Applet;
import java.awt.Button;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Label;
import java.awt.TextField;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;



public class MemoryGame extends Applet implements ActionListener, Runnable {

    private Label prompt;
    private Button button;
    private TextField input, numDisplay;
    private int arrayCounter = 3, backgroundColor =0; 
    private int[] myArray = new int[arrayCounter];
    private int[] compare = new int[arrayCounter];
    private Thread delayThread;
    private boolean running = true, isCompare; 


    public void init(){
        prompt = new Label("Enter the numbers!");
        input = new TextField(20);
        numDisplay = new TextField(20);
        numDisplay.setEditable(false);
        button = new Button("Enter");

        add(prompt);
        add(input);
        add(numDisplay);
        add(button);
        button.addActionListener(this);

        populateArray();
        delayThread = new Thread(this); 
        delayThread.start();


    }
    public void paint(Graphics g){

        if(backgroundColor == 1){
            setBackground (Color.green);
        }
        else if(backgroundColor == 2){
            setBackground (Color.red);
        }
    }


    public void populateArray() {
        GenerateNumbers a = new GenerateNumbers();
        myArray = a.returnArray(); 


        int count = 1;
        for(int i = 0; i < myArray.length;i++){
            System.out.println("index: " + count + " : " + myArray[i]);
            count++;
            numDisplay.setText(" ");
        } //for testing purpose
    }

    @Override
    public void actionPerformed(ActionEvent e)throws StringIndexOutOfBoundsException {
        String answer ="", newNumber="";
        String[] stringArray = new String[arrayCounter];
        int counterOne = 0, counterTwo = 2;
        try{
            answer = input.getText();
            for(int i = 0; i < arrayCounter;i++){
                newNumber = answer.substring(counterOne, counterTwo);
                stringArray[i] = newNumber;
                counterOne += 3;
                counterTwo += 3;
            }
        }catch(NumberFormatException ex){
            ex.printStackTrace();
        }

        for(int i = 0; i < arrayCounter;i++){
            compare[i] = Integer.parseInt(stringArray[i]);
        }

        for(int i = 0; i < arrayCounter;i++){
            if(myArray[i] != compare[i]){
                backgroundColor = 2;
                input.setText("Wrong");
                repaint();
            }
            else{
                backgroundColor =1;
                input.setText("RIGHT!");//testing
                repaint();
            }

        }

    }

    public void destroy(){
        running = false; 
    }

    @Override
    public void run() {
        while(running){
            String numberString = "" ,stringTwo = "  ";
            for(int i = 0; i < arrayCounter;i++){
                numberString += myArray[i] + stringTwo;
                numDisplay.setText(numberString);
            }
            try{
                delayThread.sleep(3500);
            }catch(InterruptedException e){
                e.printStackTrace();
                Thread.currentThread().interrupt();
            }
            numDisplay.setText(" ");
            destroy();
        }
    }

}

Answer 1

在调用 answer.substring(counterOne, counterTwo) 之前，您必须确保0 <= counterOne < answer.length()和counterTwo <= answer.length() .

substring会抛出IndexOutOfBoundsException如果the beginIndex is negative, or endIndex is larger than the length of this String object, or beginIndex is larger than endIndex .

编辑:

让我们尝试解决您的问题。以下循环的逻辑有缺陷:

        answer = input.getText();
        for(int i = 0; i < arrayCounter;i++){
            newNumber = answer.substring(counterOne, counterTwo);
            stringArray[i] = newNumber;
            counterOne += 3;
            counterTwo += 3;
        }

如果我理解你想要做什么，你期望输入字符串(存储为 answer )包含数字，你创建这些数字的数组，并将其与正确数字的数组进行比较。

但是，只有当用户的答案以“11x22x33...”之类的内容开头时，上述循环才有效，因为您希望提取 arrayCounter (=3) 个来自该输入字符串的每个 2 个字符的子字符串，并且您将从字符串的位置 (0,1) (3,4) (6,7) 中提取它们。这意味着如果字符串少于 8 个字符，您将得到 StringIndexOutOfBoundsException .

您不应假设输入字符串中数字的长度或数字的数量。更好、更简单的解决方案是:

stringArray = answer.split(" ");

这会在空格处分割输入数组。请注意，您将获得的数组的长度不一定与正确答案的长度匹配，因此您必须比较长度。