Reverse string. A Java string contains a sequence of characters. To create another version of that string, we can reverse it. This can be used to form a string key.
Java method notes. We use many parts from Java to reverse a string. We create a mutable char array buffer. We use charAt to get (in inverse order) chars from the original string.
Method example. We introduce the reverseString method. First we allocate a char array with a size equal to the string's length. Then we loop the array elements.
And We assign the array elements to a string character indexed from the opposite (inverted) side. This reverses the characters.
public class Program {
public static String reverseString(String value) {
// Create a char buffer.
char[] array = new char[value.length()];
for (int i = 0; i < array.length; i++) {
// Assign to the array from the string in reverse order.// ... charAt uses an index from the last.
array[i] = value.charAt(value.length() - i - 1);
}
return new String(array);
}
public static void main(String[] args) {
// Test our reverse string method.
String original = "abc";
String reversed = reverseString(original);
System.out.println(original);
System.out.println(reversed);
original = "qwerty";
reversed = reverseString(original);
System.out.println(original);
System.out.println(reversed);
}
}abc
cba
qwerty
ytrewq
A discussion. The Arrays class has no reverse method. This means that we must reverse these characters manually. We find a reverse() on Collections.
But Collections.reverse would require the string be converted into a collection like an ArrayList. This would hinder performance.
A review. String reversal is not a common requirement. But for certain problems (like key generation) or for homework assignments, it has use.
Dot Net Perls is a collection of tested code examples. Pages are continually updated to stay current, with code correctness a top priority.
Sam Allen is passionate about computer languages. In the past, his work has been recommended by Apple and Microsoft and he has studied computers at a selective university in the United States.
This page was last updated on Jan 9, 2022 (image).
