COMP2511 Week 2

Agenda

Admin Stuff
Code Review
Documentation
Basic Inheritance & Polymorphism (Code Demo)
Access Modifiers & Packages

Admin Stuff

Assignment 1 has been released
- Due Week 5 Friday, 5pm (17th March)
- 20% of the Course mark
Help sessions exist!
Solutions for tute1

Code Review

package shapes;

public class Shape {
    public String color;

    public Shape(String color) {
        System.out.println("Inside Shape constructor");
        this.color = color;
    }
}

public class Rectangle extends Shape {
    public int height;
    public int width;

    public Rectangle(String color) {
        super(color);
        System.out.println("Inside Rectangle constructor with one argument");
    }

    public Rectangle(String name, int width, int height) {
        this(name);
        this.width = width;
        this.height = height;
        System.out.println("Inside Rectangle constructor with three arguments");
    }

    public static void main(String[] args) {
        Rectangle r = new Rectangle("red", 10, 20);
        System.out.println(r.color);
        System.out.println(r.width);
        System.out.println(r.height);
    }
}

What is the difference between super and this?

Shape.java

Rectangle.java

Code Review

package shapes;

public class Shape {
    public String color;

    public Shape(String color) {
        System.out.println("Inside Shape constructor");
        this.color = color;
    }
}

public class Rectangle extends Shape {
    public int height;
    public int width;

    public Rectangle(String color) {
        super(color);
        System.out.println("Inside Rectangle constructor with one argument");
    }

    public Rectangle(String color, int width, int height) {
        this(color);
        this.width = width;
        this.height = height;
        System.out.println("Inside Rectangle constructor with three arguments");
    }

    public static void main(String[] args) {
        Rectangle r = new Rectangle("red", 10, 20);
        System.out.println(r.color);
        System.out.println(r.width);
        System.out.println(r.height);
    }
}

What is the difference between super and this?
- super refers to the superclass whereas this refers to the current class

Shape.java

Rectangle.java

Code Review

package shapes;

public class Shape {
    public String color;

    public Shape(String color) {
        System.out.println("Inside Shape constructor");
        this.color = color;
    }
}

public class Rectangle extends Shape {
    public int height;
    public int width;

    public Rectangle(String color) {
        super(color);
        System.out.println("Inside Rectangle constructor with one argument");
    }

    public Rectangle(String color, int width, int height) {
        this(color);
        this.width = width;
        this.height = height;
        System.out.println("Inside Rectangle constructor with three arguments");
    }

    public static void main(String[] args) {
        Rectangle r = new Rectangle("red", 10, 20);
        System.out.println(r.color);
        System.out.println(r.width);
        System.out.println(r.height);
    }
}

What is the difference between super and this?
- super refers to the superclass whereas this refers to the current class
What about super(...) and this(...)?

Shape.java

Rectangle.java

Code Review

public class Shape {
    public String color;

    public Shape(String color) {
        System.out.println("Inside Shape constructor");
        this.color = color;
    }
}

public class Rectangle extends Shape {
    public int height;
    public int width;

    public Rectangle(String color) {
        super(color);
        System.out.println("Inside Rectangle constructor with one argument");
    }

    public Rectangle(String color, int width, int height) {
        this(color);
        this.width = width;
        this.height = height;
        System.out.println("Inside Rectangle constructor with three arguments");
    }

    public static void main(String[] args) {
        Rectangle r = new Rectangle("red", 10, 20);
        System.out.println(r.color);
        System.out.println(r.width);
        System.out.println(r.height);
    }
}

What is the difference between super and this?
- super refers to the superclass whereas this refers to the current class
What about super(...) and this(...)?
- super() calls the parent class constructor
- this() calls the current class constructor

Shape.java

Rectangle.java

Code Review

public class Shape {
    public String color;

    public Shape(String color) {
        System.out.println("Inside Shape constructor");
        this.color = color;
    }
}

public class Rectangle extends Shape {
    public int height;
    public int width;

    public Rectangle(String color) {
        super(color);
        System.out.println("Inside Rectangle constructor with one argument");
    }

    public Rectangle(String color, int width, int height) {
        this(color);
        this.width = width;
        this.height = height;
        System.out.println("Inside Rectangle constructor with three arguments");
    }

    public static void main(String[] args) {
        Rectangle r = new Rectangle("red", 10, 20);
        System.out.println(r.color);
        System.out.println(r.width);
        System.out.println(r.height);
    }
}

What is the difference between super and this?
- super refers to the superclass whereas this refers to the current class
What about super(...) and this(...)?
- super() calls the parent class constructor
- this() calls the current class constructor

Shape.java

Rectangle.java

Code Review

public class Circle {

    private static final double pi = 3.14159;
    private int x, y;
    private int r;
	
    // Only 1 variable for all Circle objects
    public static int numberOfCircles = 0; 

    public Circle() {
        numberOfCircles++;
    }
    
    public double circumference() {
        return 2 * pi * r;
    }
    
    public static void main(String[] args) {
        System.out.println("Number of circles: " + Circle.numberOfCircles); // 0
        
        Circle c1 = new Circle();
        System.out.println("Number of circles: " + Circle.numberOfCircles); // 1
        
        Circle c2 = new Circle();
        System.out.println("Number of circles: " + Circle.numberOfCircles); // 2
    }
}

What are static fields and methods?

Code Review

public class Circle {

    private static final double pi = 3.14159;
    private int x, y;
    private int r;
	
    // Only 1 variable for all Circle objects
    public static int numberOfCircles = 0; 

    public Circle() {
        numberOfCircles++;
    }
    
    public double circumference() {
        return 2 * pi * r;
    }
    
    public static void main(String[] args) {
        System.out.println("Number of circles: " + Circle.numberOfCircles); // 0
        
        Circle c1 = new Circle();
        System.out.println("Number of circles: " + Circle.numberOfCircles); // 1
        
        Circle c2 = new Circle();
        System.out.println("Number of circles: " + Circle.numberOfCircles); // 2
    }
}

What are static fields and methods?
- Static fields are variables that are common and available to all instances of a Class. They belong to the Class, rather than an instance.

Code Review

public class Circle {

    private static final double pi = 3.14159;
    private int x, y;
    private int r;
	
    // Only 1 variable for all Circle objects
    public static int numberOfCircles = 0; 

    public Circle() {
        numberOfCircles++;
    }
    
    public double circumference() {
        return 2 * pi * r;
    }
    
    public static void main(String[] args) {
        System.out.println("Number of circles: " + Circle.numberOfCircles); // 0
        
        Circle c1 = new Circle();
        System.out.println("Number of circles: " + Circle.numberOfCircles); // 1
        
        Circle c2 = new Circle();
        System.out.println("Number of circles: " + Circle.numberOfCircles); // 2
    }
}

What are static fields and methods?
- Static fields are variables that are common and available to all instances of a Class. They belong to the Class, rather than an instance.
- Methods are a block of code that performs a task. You can think of them as functions of a class.

Code Review

Documentation

What is meant by self-documenting code?

Documentation

What is meant by self-documenting code?
- It is inherently easy to read through the use of meaningful variables, function names, clear logic.

Documentation

What is meant by self-documenting code?
- It is readable inherently, through things like meaningful variables and function names.
When can comments be bad (code smell)?

Documentation

What is meant by self-documenting code?
- It is readable inherently, through the use of meaningful variables and function names.
When can comments be bad (code smell)?
- Comments go stale/outdated comments
- Comments are literally reiterating your code.

Documentation

JavaDoc is one way of documenting in Java.
JavaDoc is a way of writing your comments
It mainly targets class definitions and method/function definitions.
in COMP2511, you will not have to use JavaDoc documentation unless asked.

/**
 * File class that stores content under a file name
 */
public class File {
    /**
     * Constructor used to create a file
     * @param fileName the name of the file
     * @param content contents of the file
     */
    public File(String fileName, String content) {}
 
    /**
     * Constructor used to make a partial file when receiving a new file
     * I.e., content.length() != fileSize with no compression
     * @param fileName
     * @param fileSize
     */
    protected File(String fileName, int fileSize) {}
    
    /**
     * Checks if transfer has been completed
     * @return true if it has been completed
     */
    public boolean hasTransferBeenCompleted() {}
}

Documentation

VSCode Extensions

Java Code Generators: generate methods for classes such as getters and setters (recommend)
Javadoc Tools: generate Javadoc comments for methods within a class

Code Demo

Create an Employee class with a name and salary
Create a constructor which sets the name and salary
Create getters & setters with JavaDoc
Create a Manager Class that inherits Employee with a hireDate
Override toString() method for both classes
Override equals() method for both classes

Access Modifiers

public class Circle {
    int a; // Default
    private int b; // Private
    protected int c; // Protected
    public int d; // Public
}