Java：for 循环使用字符串 charAt 方法崩溃

Question

I have a bug in this block of code. The debugger suggest it´s cause is this line of code char chr = getSecretWord.charAt(i);

What this code does is look for a match between userInput and secretWord . I have the for loop to go through the length of the secretWord letters one by one, and if there is a letter matching return true. If not, return false... but the program crashes when it is suppose to just return false... I guess it is something with this line, but do not know exactly what getSecretWord.charAt(i);

    private boolean isMatchingSecretWord(String userInput)
{
    String secretWord = "";
    String getSecretWord = getSecretWord();
    for (int i = 0; i <= getSecretWord.length();i++)
        {
        char chr = getSecretWord.charAt(i);
        secretWord = ""+chr;

        if (secretWord.equals(userInput))
        {
            println("is true");
            return true;
        }
    }
    return false;
}

As an side note, is what I´ve done with this code correct, assigning the getSecretWorld() Method to a String so I can use the Strings method length() ?

String getSecretWord = getSecretWord();

for (int i = 0; i <= getSecretWord.length();i++)

Debug code:

Exception in thread "Thread-4" java.lang.StringIndexOutOfBoundsException: String index out of range: 4    
    at java.lang.String.charAt(String.java:686)    
    at Hangman.isMatchingSecretWord(Hangman.java:49)    
    at Hangman.userInput(Hangman.java:34)    
    at Hangman.run(Hangman.java:20)*

Answer 1

for (int i = 0; i <= getSecretWord.length(); i++)

should be:

for (int i = 0; i < getSecretWord.length(); i++)
//               ^^^
//             see here

The valid indexes for an n -character string (or an n -element array) are 0 through n-1 inclusive.

So, if your secret word is xyyzy , the valid indexes are zero through four. Your original loop iterates with i set to zero through five, hence the problem.

---

But there seems to be a lot of unnecessary code in there, when you could get away with something simple.

First, I would remove a source of confusion - the function name sounds like the user input and the secret word have to match completely whereas your comment indicates otherwise:

Thanks, this works. But the reason for the loops is that the user enters one letter, I want to see if that letter is within the SecretWord. (it´sa hangman game).

In that case, you simply want to see if the single character exists in the secret word. I would change the function name to suit and, even then, it can be done with a lot less code:

private boolean isInSecretWord (String userInput) {
    String secretWord = getSecretWord();
    return secretWord.contains(userInput);
}

Answer 2

You were getting out of bounds error as your for loop wasn't looping correctly, I have modified it so that the loop doesn't go out of bounds and also your secretWord variable wasn't populating correctly, the code should now work as intended :)

private boolean isMatchingSecretWord(String userInput)
{
    String secretWord = "";
    String getSecretWord = getSecretWord();
    for (int i = 0; i < getSecretWord.length();i++)
        {
        char chr = getSecretWord.charAt(i);
        secretWord = secretWord + chr;

        if (secretWord.equals(userInput))
        {
            println("is true");
            return true;
        }
    }
    return false;
}