这个问题在这里已经有了答案：

什么是indexoutofboundsexception？我该怎么修[重复]（1个答案）
上个月关门了。

public class DuplicateLetters {

    // CW2.2 Lab-Group-06 Question 5
    // You are given two non-empty strings source and target, all lowercase letters, from a user.
    // The user intends to type the string given in target.
    // However, due to using an old keyboard,
    // when the user was typing, a number characters may be duplicated, and typed one or more times.
    // The source is what the user actually typed, which may or may not be the intended target.
    // Return true if and only if it is possible that some characters of target have been duplicated in source,
    // while the user intended to type the target string.
    // You must use String methods in lecture notes.
    // You must NOT use StringBuilder or Regular Expression methods.

    public static boolean duplicateLetters(String source, String target) {
        boolean test = false;

        for(int i=0; i<source.length(); i++) {
            for(int j=i; j<target.length(); j++) {
                if(Character.toString(source.charAt(i)).equals(Character.toString(target.charAt(j)))) {
                    test = true;
                }
                else {
                    test = false;
                    j--;    
                }
                i++;
            }
        }
        return test;
    }

    public static void main(String[] args) {

        System.out.println(duplicateLetters("andddrew", "andrew"));
        // true, there are duplicated letters typed

        System.out.println(duplicateLetters("lllejiiee", "leejie"));
        // false, note the initial letter e
        // there is only one initial e in the source, whereas there is a double initial ee in the target

        System.out.println(duplicateLetters("cherry", "cherry"));
        // true, no duplicated letters typed this time
    }

这是我针对这个问题编写的代码，但它不断得到java.lang.stringindexoutofbounds错误。所以，我想知道我的代码有什么问题，以及如何改进。