How can I generate a random number within a certain range with Java?

I want to generate a random number in Java. It can be of integer, byte or float type, but all I really need it is to generate a random number. This is what I'm doing:

1. Generate a random number within a certain range (e.g. 5 through 20).
2. Take the number and store it within a variable.
3. Perform arithmetic on it.

Here's the code:

import java.util.HashMap;

public class Attack {
    public static void main(String[] args) {
        HashMap<String, Integer> attacks = new HashMap<String, Integer>();
        attacks.put("Punch", 1);
        attacks.put("Uppercut", 3);
        attacks.put("Roundhouse Kick", 5);

        int actionPoints = // Code for random number generation

        System.out.println("A brigade integrant appeared!");
        System.out.println("What do you do?");
        System.out.println("1: Punch [1 AP], 2: Uppercut [3 AP], 3: Roundhouse Kick [5 AP]");
        System.out.println("You have " + actionPoints + " Action Points.");
        Scanner reader = new Scanner(System.in);
        System.out.println("Enter a number: ");
        int n = reader.nextInt();
        reader.close();

        if n == 1 {
            System.out.println("The brigade integrant takes 2 HP of damage!");
        }
        else if n == 2 {
            System.out.println("The brigade integrant takes 5 HP of damage!");
        }
        else if n == 3 {
            System.out.println("The brigade integrant takes 8 HP of damage!");
        }
    }
}