Introduction to OOP

• understanding the concepts of class and object
• using contructors to initialize objects
• overloading methods
• static keyword
• this keyword

Java Oracle Tutorial - OOP Concepts
Principiile programarii orientate pe obiecte
Ciclul de viaţă al obiectelor

A class Sensor contains:

• One instance variable 'value' (of type int);
• One default constructor which initialize the value to -1;
• One change(int k) method which add to the current sensor value k;
• One toString() method which returns the current value of the sensor;

Write a class which models the class Sensor . Write a class TestSensor which test Sensor class.

A class called Circle contains:

• Two private instance variables: radius (of type double) and color (of type String), with default value of 1.0 and “red”, respectively.
• Two overloaded constructors;
• Two public methods: getRadius() and getArea().

Write a class which models the class Circle. Write a class TestCircle which test Circle class.

A class called Author contains:

• Three private instance variables: name (String), email (String), and gender (char of either 'm' or 'f');
• One constructor to initialize the name, email and gender with the given values;
• public Author (String name, String email, char gender) {……}
• (There is no default constructor for Author, as there are no defaults for name, email and gender.)
• public getters/setters: getName(), getEmail(), setEmail(), and getGender();
• (There are no setters for name and gender, as these attributes cannot be changed.)
• A toString() method that returns “author-name (gender) at email”, e.g., “My Name (m) at myemail@somewhere.com”.

Write the Author class. Also write a test program called TestAuthor to test the constructor and public methods.

A class called MyPoint, which models a 2D point with x and y coordinates contains:

• Two instance variables x (int) and y (int).
• A “no-argument” (or “no-arg”) constructor that construct a point at (0, 0).
• A constructor that constructs a point with the given x and y coordinates.
• Getter and setter for the instance variables x and y.
• A method setXY() to set both x and y.
• A toString() method that returns a string description of the instance in the format “(x, y)”.
• A method called distance(int x, int y) that returns the distance from this point to another point at the given (x, y) coordinates.
• An overloaded distance(MyPoint another) that returns the distance from this point to the given MyPoint instance another.

Write the code for the class MyPoint. Also write a test class (called TestMyPoint) to test all the methods defined in the class.

Modify Flower class from Ciclul de viaţă al obiectelor so that it keeps track of the number of constructed object. Add a method which returns the number of constructed objects. Use 'static' variables and methods for implementing this task.