Practice 1: Instantiable Classes

Write a class called Fountain. Objects of this class will have three component variables:

• the capacity of the fountain (in liters),
• the amount of water currently in the fountain (also in liters), and
• whether the fountain is currently running or not.

Fountains start out empty, in the off state, with a given capacity. For example,

Fountain fountain = new Fountain(200);

should create a Fountain object representing an empty fountain which is not running and has a capacity of 200 liters of water.

Besides the constructor, you will need three additional methods: add(int liters), toggle(), and look().

• When public void add(int liters) is called, the given number of liters of water are added to the fountain. (Note that liters could be negative, in which case water will be removed from the fountain.) However:
  • The fountain cannot hold more than its capacity. If the total contents of the fountain would exceed its capacity, the excess liters overflow and the fountain will contain exactly its capacity.
  • The contents of the fountain cannot become negative. If the fountain becomes empty then it should automatically turn off.

• When public void toggle() is called:

  • If the fountain is on, it will turn off.
  • If the fountain is off but it is empty, it cannot turn on.
  • If the fountain is off and contains some water, it will turn on.
• When public String look() is called, it returns a string explaining what the fountain looks like. The string should say whether the fountain is on or off, and how much water it contains.

Here is a sample Main class in Java that tests the fountain.

public class Main {
  public static void main(String[] args) {
    Fountain f = new Fountain(200);
    System.out.println(f.look());  
    f.toggle();
    System.out.println(f.look());
    f.add(120);
    System.out.println(f.look());
    f.toggle();
    System.out.println(f.look());
    f.add(397);
    System.out.println(f.look());
    f.toggle();
    System.out.println(f.look());
    f.toggle();
    System.out.println(f.look());
    f.add(-90);
    System.out.println(f.look());
    f.add(-200);
    System.out.println(f.look());
 }
}

When you run the above code, here is a sample of output that you could see. Your implementation does not have to produce exactly the same messages, as long as they contain the same information.

The fountain is off. It contains 0 liters of water.
The fountain is off. It contains 0 liters of water.
The fountain is off. It contains 120 liters of water.
Sploosh! The fountain is on. It contains 120 liters of water.
Sploosh! The fountain is on. It contains 200 liters of water.
The fountain is off. It contains 200 liters of water.
Sploosh! The fountain is on. It contains 200 liters of water.
Sploosh! The fountain is on. It contains 110 liters of water.
The fountain is off. It contains 0 liters of water.