Here's an example Java program that reverses a number:

public class ReverseNumber {
    public static void main(String[] args) {
        int num = 12345;
        int reversed = 0;

        while (num != 0) {
            int digit = num % 10;
            reversed = reversed * 10 + digit;
            num /= 10;
        }

        System.out.println("Original number: " + 12345);
        System.out.println("Reversed number: " + reversed);
    }
}

This program first initializes a variable num with the original number to be reversed, and a variable reversed with an initial value of 0. The program then uses a while loop to repeatedly extract the rightmost digit of num using the modulus operator %, add it to the reversed number reversed by multiplying it by 10 and adding the current digit, and divide num by 10 to remove the rightmost digit. This process is repeated until num becomes 0.

The program then prints the original and reversed numbers to the console.

The output of this program would be:

Original number: 12345
Reversed number: 54321