The reverse() method in Java is a built-in function of the StringBuilder class that is used to reverse a string or sequence of characters. This method can be used to reverse an integer by converting it to a string first, and then using the StringBuilder class to reverse the string.

The reverse() method takes no arguments and returns the reversed StringBuilder object. To use this method, you first need to create an instance of the StringBuilder class and pass the integer value to its constructor. Then, you can use the reverse() method to reverse the string representation of the integer, and finally, convert it back to an integer using the parseInt() method of the Integer class.

Here's an example code snippet that demonstrates the usage of the reverse() method to reverse an integer: 

int num = 12345;
StringBuilder sb = new StringBuilder(Integer.toString(num));
sb.reverse();
int reversedNum = Integer.parseInt(sb.toString());
System.out.println(reversedNum); // Output: 54321

In this code snippet, we first convert the integer num to a string using the toString() method of the Integer class. Then, we create a new StringBuilder instance and pass the string representation of num to its constructor. Next, we call the reverse() method of the StringBuilder object to reverse the string. Finally, we convert the reversed string back to an integer using the parseInt() method of the Integer class and print the result.