I know how to reverse a string but I was just trying for an alternate way to do the same using a character array. Just tell me why the wrong output comes? a has the String
char[] c = a.toCharArray();
int j = c.length;
char c2[] = c;
for(int i = 0; i < j; i++){
c2[i] = c[j - i - 1];
}
System.out.println(c2);
like giving harold gives output dloold
You are reading and writing to the same array. This:
char c2[]=c;
is not correct
You want:
char c2[]= new char[c.length];
There is no real need to use two arrays, and when you do a reference copy you end up working on the same array anyway.
Remember to test your algorithm using an empty array, null, an array with even length and one with odd length.
Here is a single array solution including simple test prints.
public class ReverseTest {
public static String reverse(String s) {
if (s == null)
return null;
char[] ca = s.toCharArray();
for (int i = 0; i < ca.length/2; i++) {
int j = ca.length-i-1;
char c = ca[i];
ca[i] = ca[j];
ca[j] = c;
}
return String.valueOf(ca);
}
public static void main(String[] args) {
System.out.println(reverse(null));
System.out.println(reverse(""));
System.out.println(reverse("54321"));
System.out.println(reverse("4321"));
}
}
Prints:
null
empty line
12345
1234
This is a reference problem.
char c2[]=c;
This does not copy the array, only its reference. So c2 and c are the same arrays. In your loop you override the first chars with the last ones. Simplest solution is to use:
char c2[]= new char[j];
So you have two arrays and no reference problems.
Alternativly you can swap the array inplace. Loop throught it until the half and swap elements from first and second half.
Your assignment char c2[]=c; assigns reference of c to c2. You should create array with the same length with c.
So you should either write;
char c2[] = new char[j];
or
char c2[] = a. toCharArray()
to create array with difference reference in memory.
As other answers have mentioned, you must stop halfway through the array.
I'd just like to add that Java has the StringBuilder.reverse() method, which also operates on a character array in place. The following is adapted from the official source code:
private static String reverse(String s) {
char[] chars = s.toCharArray();
int length = s.length();
for (int j = (length-1) / 2; j >= 0; j--) {
int k = length - j - 1;
char cj = chars[j];
char ck = chars[k];
chars[j] = ck;
chars[k] = cj;
}
return new String(chars);
}
