宾果歌词代码Java.lang.stringindexoutofbounds？

Question

我是编程新手，我已经编写了一个bingo类，用于输入bingo的歌词。代码如下：

public class BingoLyrics {
String lineOne = "There was a farmer had a dog and Bingo was his name, oh." ;
String lineTwo = "BINGO" ;
String lineThree = "And Bingo was his name, oh." ;
int starCount = 1 ;
public void bingoLyrics ( ) {
    while (starCount != 7) {
System.out.println (lineOne) ;
System.out.println (lineTwo + ", " + lineTwo + ", " +  lineTwo) ;
System.out.println (lineThree) ;
lineTwo = "*" + (lineTwo.substring(starCount)) ;
if (lineTwo.length() == 4) {
    lineTwo = "*" + lineTwo ;
}
else if (lineTwo.length() == 3) {
    lineTwo = "**" + lineTwo;
}
else if (lineTwo.length() == 2) {
    lineTwo = "***" + lineTwo;
}
else if (lineTwo.length() == 1) {
    lineTwo = "****" + lineTwo;
}
starCount = starCount + 1 ;
 }
 }
 }

它可以工作，但我得到了行lineTwo = "*“+ (lineTwo.substring(starCount))；的java.lang.stringindexoutofbounds。它为什么要这样做？有什么办法可以解决吗？

Answer 1

您会得到一个StringOutOfBoundsException，因为在循环的最后一次迭代中，starCount是6，但是字符串只有5个字符。您可以使用StringBuilder，而不是对第二行使用字符串。这更容易，因为您可以替换指定索引处的字符。

public class BingoLyrics {
String lineOne = "There was a farmer had a dog and Bingo was his name, oh.";
StringBuilder lineTwo = new StringBuilder("BINGO");
String lineThree = "And Bingo was his name, oh.";
int starCount = 0;

public void bingoLyrics() {
    while (starCount < 6) {
        System.out.println(lineOne);
        System.out.println(lineTwo + ", " + lineTwo + ", " + lineTwo);
        System.out.println(lineThree);
        lineTwo.replace(starCount, starCount + 1, "*");
        starCount = starCount + 1;
    }
}

}