Cloud Compute Hierarchy

12 points

This question requires a question-specific abstract class and a question-specific interface. Every concrete instance type must extend the class and implement the interface.

Create an abstract class CloudInstance in CloudInstance.java:

Protected fields: String instanceId, double baseHourlyRate.
Constructor: CloudInstance(String instanceId, double baseHourlyRate).
Abstract method: public abstract double computeCost(double hoursRunning);

Create an interface Billable in Billable.java:

Abstract method: double costFor(double hours);
Default method: default double dailyEstimate(): returns costFor(24.0).
Default method: default boolean exceedsBudget(double hours, double budget): returns true when costFor(hours) is strictly greater than budget.

Create OnDemandInstance in OnDemandInstance.java extending CloudInstance and implementing Billable:

Constructor: OnDemandInstance(String instanceId, double baseHourlyRate).
computeCost(double hoursRunning): baseHourlyRate * hoursRunning.
costFor(double hours) must return the same value as computeCost(hours).

Create SpotInstance in SpotInstance.java extending CloudInstance and implementing Billable:

Private field: double bidDiscountPercent (e.g. 60.0 for 60% off).
Constructor: SpotInstance(String instanceId, double baseHourlyRate, double bidDiscountPercent) using super.
computeCost(double hoursRunning):
effectiveRate = baseHourlyRate * (1.0 - (bidDiscountPercent / 100.0)).
Base cost is effectiveRate * hoursRunning.
If hoursRunning > 24.0, subtract a $2.00 interruption-risk rebate; the final cost cannot drop below 0.0.
costFor(double hours) must return the same value as computeCost(hours).

Sample Run

CloudInstance onDemand = new OnDemandInstance("i-ondemand", 2.00);
CloudInstance spot = new SpotInstance("i-spot", 2.00, 50.0); // $1.00/hr
System.out.println("On-Demand (10h): " + onDemand.computeCost(10.0));
System.out.println("Spot (10h): " + spot.computeCost(10.0));
System.out.println("Spot (30h): " + spot.computeCost(30.0)); // 30*1.0 - 2.0 = 28.0

Expected Output

On-Demand (10h): 20.0
Spot (10h): 10.0
Spot (30h): 28.0

Test Cases

VisibleTest 1 [Visible] (Sample Run)
On-demand linear rate, spot 50% discount, spot > 24h rebate.
Hidden6 hidden tests
Additional edge cases run when you grade, but their details are not shown.

Java 25

Press Compile & Run to compile and execute your code (OpenJDK 25). Output appears here.