需要帮助来修复以下代码的arrayoutofboundary异常

Question

How to fix arrayOutOfBoundException error message for the below code. This seem to be logically correct for me. But I'm not sure why I get this error. Need help on this

public class list  {

    public String reverseStr(String input){
        String reverString = input;
        int j=0;

        Character rev[] = new Character[reverString.length()-1];

        for(int i= reverString.length()-1;i> 0; --i){

            for(j = 0;j<= reverString.length()-1; ++j){
             rev[j] = reverString.charAt(i);
            }

        }
        String output = String.valueOf(rev[j]);
        return output;
    }

    public static void main(String args[]){
        String reverse = "Ambika";
        list li = new list();
        System.out.println("The reverse of " + reverse + " is " + li.reverseStr(reverse));
    }
}

Answer 1

When inner for loop breaks, j will reach beyond the array bounds. add j-- before the line String output = String.valueOf(rev[j]);

On side note, you should make rev array big enough to hole whole string

  Character rev[] = new Character[reverString.length()];

Answer 2

for(j = 0;j<= reverString.length()-1; ++j){

改成

 for(j = 0;j< reverString.length()-1; ++j){

Answer 3

class Untitled {

    public static String reverse( final String s )
    {
        return new StringBuilder(s).reverse().toString();            
    }

    public static void main(String[] args) {
        System.out.println( reverse( "Josh" ) );
    }
}

hsoJ

Answer 4

You initialized rev with size one less than the length of reverString

 Character rev[] = new Character[reverString.length()-1];

Change it to

Character rev[] = new Character[reverString.length()];

Actually, your whole idea of nested for-loop is a mess. You can simplify your program as follows;

public class list {

    public String reverseStr(String input) {
        String reverString = input;
        int j = 0;

        char rev[] = new char[reverString.length()];

        for (int i = reverString.length() - 1; i >= 0; --i) {

            rev[j++] = reverString.charAt(i);
        }

        String output = new String(rev);
        return output;
    }

    public static void main(String args[]) {
        String reverse = "Ambika";
        list li = new list();
        System.out.println("The reverse of " + reverse + " is "
                + li.reverseStr(reverse));
    }
}

Answer 5

There are so many issues in your source,

1. You are defining an array with one length less than the acutual Sting size.

   Character rev[] = new Character[reverString.length()-1];

   It should have been,

   Character rev[] = new Character[reverString.length()-1];

2. Printing the value using the Index

   String output = String.valueOf(rev[j]);

   You can print using for loop

   for (Character c : rev) System.out.print(c);

3. You don't need two loops. One loop should be sufficient as below

   int j = 0; for (int i = reverString.length() - 1; i >= 0; --i) { rev[j] = reverString.charAt(i); j++; }

4. Finally you don't need a separate array to hold your result. You can hold the result in a String or StringBuilder .

Answer 6

Couple of things I noticed in your program. 1. You do not need two loops to reverse the string, you can use one loop for traversing and increase the value of j to move.

int j=0;     
for(int i= reverString.length()-1;i>= 0; --i){           
             rev[j++] = reverString.charAt(i);
        }

1. Second if you noticed the above loop you will find that it is actually being invoked 6 time for value of i which is ( 5,4,3,2,1,0), so you need a array of size 6 which mean the size of rev should be 6 which is reverString.length() Please refer the code below.

    public class List { public String reverseStr(String input){ String reverString = input; int j=0; char rev[] = new char[reverString.length()-1]; for(int i= reverString.length()-1;i>= 0; --i){ rev[j++] = reverString.charAt(i); } String output =String.valueOf(rev); return output; } public static void main(String args[]){ String reverse = "Ambika"; List li = new List(); System.out.println("The reverse of " + reverse + " is " + li.reverseStr(reverse)); } 

   }