JAVA中最后一个字符出现的次数只使用String

Question

I'm doing a part of a program, where I should see the number of times the last character appears in JAVA.

The problem is that I am new with the use of Strings ( and only can use String ). Informing a bit I have seen that with equals I can compare Strings. And with substring I can select each of the letters one by one in a loop. The problem comes when I compile, that I go out of the index of the String. And I do not understand why, since I only get to .length - 1

    String aux;
    int cont = 0;

    aux = cadena.substring(cadena.length()-1);

    for (int i = 0; i < cadena.length()-1; i++) {
        if(cadena.substring(i,1).equals(aux)) {
            cont++;
        }
    }

java.lang.StringIndexOutOfBoundsException: String index out of range:-1

In this line

if(cadena.substring(i,1).equals(aux))

Answer 1

what you have done is like "Hello".substring(3, 1)

substring method takes two arguments startIndex and endIndex . so end index should always be greater than start index.

In cadena.substring(i,1) , the value of i will go from 0 to cadena.length()-2 , because of condition i<cadena.length()-1

Answer 2

You can do something like this:

int count = 0;

char lastChar = cadena.charAt(cadena.length()-1);

for (int i = 0; i < cadena.length()-1; i++) {
   if(lastChar==cadena.charAt(i)) count++;
}