Sure, here's a Java program to swap two numbers:

public class SwapNumbers {
    public static void main(String[] args) {
        int num1 = 5;
        int num2 = 10;
        
        System.out.println("Before swapping:");
        System.out.println("num1 = " + num1);
        System.out.println("num2 = " + num2);
        
        int temp = num1;
        num1 = num2;
        num2 = temp;
        
        System.out.println("After swapping:");
        System.out.println("num1 = " + num1);
        System.out.println("num2 = " + num2);
    }
}

In this program, we first define two integer variables num1 and num2 to represent the numbers to swap. We then print out the values of num1 and num2 before swapping.

We then define a third integer variable temp and assign num1 to it. We can think of this as temporarily storing the value of num1 so that we don't lose it when we overwrite num1 with num2.

We then assign num2 to num1 and temp to num2, effectively swapping the values of num1 and num2.

Finally, we print out the values of num1 and num2 after swapping.

Note that we can also swap two numbers without using a temporary variable by using arithmetic operations, as follows:

num1 = num1 + num2;
num2 = num1 - num2;
num1 = num1 - num2;

However, this method is less readable and may be less efficient on some platforms.