Feb 15: Writing Classes

Learning Objectives

After today's class, you should be able to:

• Interpret a UML class diagram and stub out the corresponding code.
• Write JUnit tests that create objects and assert non-static methods.
• Draw a memory diagram that includes variables, arrays, and objects.

Reminders

• By Friday 11pm: Do the Week 5 reading and take Quiz04
• By Monday 11pm: Complete Homework 4 (due Feb 19)

Lesson Outline

Lab04 [50 min]

• Lab 4: Writing and Testing a Class

Lecture [25 min]

How to draw pictures like Java Visualizer

a.k.a. "Memory Diagrams"

• Variables
• Methods
• Strings
• Arrays
• Objects

Example Code

public class Example {

    public static void main(String[] args) {

        Car[] cars = new Car[3];
        cars[0] = new Car("Dodge", 1989);
        cars[1] = new Car("Tesla", 2024);
        cars[2] = cars[0];

        for (Car car : cars) {
            car.accelerate();
            System.out.println(car);
        }

        System.out.println();
        race(cars);
    }

    public static void race(Car[] cars) {
        int i;
        int best = 0;
        for (i = 1; i < cars.length; i++) {
            if (cars[i].getSpeed() > cars[best].getSpeed()) {
                best = i;
            }
        }

        System.out.println("Winner at index " + best);
        System.out.println(cars[best]);
    }

}

Output

A 1989 Dodge that is going 5.0 mph
A 2024 Tesla that is going 5.0 mph
A 1989 Dodge that is going 10.0 mph

Winner at index 0
A 1989 Dodge that is going 10.0 mph

Memory Diagram

Here is the diagram I drew on the whiteboard: