Bingo歌词代码Java.lang.stringindexoutofbounds？

Question

I am new to programming and I have written a bingo class that types out the lyrics to bingo. Here is the code:

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 ;
 }
 }
 }

It works but i get a java.lang.stringindexoutofbounds for the line lineTwo = "*" + (lineTwo.substring(starCount)) ; . Why does it do this? Any way to fix?

Answer 1

You get an StringOutOfBoundsException because at the last iteration of the loop the starCount is 6, but the string is only five characters long. Instead of using a string for line two, you can use a StringBuilder. It's easier because you can replace a char at a specified index.

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;
    }
}

}