Here's a simple Java program to reverse a string:

public class ReverseString {

public static void main(String[] args) {

String original = "Hello, World!";

String reversed = reverseString(original);

System.out.println("Original string: " + original);

System.out.println("Reversed string: " + reversed);

}

public static String reverseString(String str) {

// Convert string to char array

char[] charArray = str.toCharArray();

// Initialize pointers for reversing

int left = 0;

int right = charArray.length - 1;

// Reverse the string

while (left < right) {

// Swap characters at left and right pointers

char temp = charArray[left];

charArray[left] = charArray[right];

charArray[right] = temp;

// Move pointers towards the center

left++;

right--;

}

// Convert char array back to string

return new String(charArray);

}

}

This program defines a `reverseString` method that takes a string as input and returns its reverse. In the `main` method, an example string "Hello, World!" is provided, and its reverse is printed out. You can replace `"Hello, World!"` with any string you want to reverse.