JAVA An Introduction to Java OOP Basics Mudassir Hasan

Data Types & Operators Data Types: byte, short, int, long, float, double, long , boolean, char Operators: - Arithmetic: +,-,*,/, % ( modulus-remainder ) - Relational: <, >, <=, >=, ==, != - Logical: &&, ||, !

Strings public class LearnJava { public static void main( String [] args ) { String fun = “Java is fun”; System.out.println(fun); } }

Strings (cont’d.) Date columbusDay = new Date(10, 12, 2009); System.out.println(“Columbus day was on “ + columbusDay.getDay() ); Columbus day was on 12 Stores values for columbusDay. int age = 20; // String Concatenation String youth = "He is " + age + " years old."; System.out.println(youth); He is 20 years old.

Modifiers Access Modifiers: Public – access methods of the same class and of other classes Private – access methods of the same class only Protected – access methods in the same class and also in subclasses

Constructors Initializes the fields of the new object It is called when an object is instantiated using the new keyword For example: Auto suv = new Auto( );

Constructors Default Constructor public class Auto { private int drivenMiles; private int modelYear; public Auto ( ) // same name as the class // no parameters passed, auto initialized drivenMiles to 0. modelYear = 2009; }

Constructors (cont’d.) Overloaded Constructors public Auto(int adriven Miles, int amodelYear ) // passes parameter, allows user to set their own values

Class Methods Accessor Methods, also called get Methods Get radius public int getRadius( ) { return radius; }

Class Methods Mutator Methods, also called set Methods Allows the user to set its own values in the client class public Class public void setRadius( int newRadius ) { radius = newRadius; } Client Class Circle circ = new Circle( 4 );

Arrays public class ArrayElements { public static void main(String [] args) double cells = new double [3] cells[0] = 1; cells[1] = 2; cells[2] = 3; } First index is 0. Last index is [array.length – 1]

Swapping Array int temp = array[2]; array[2] = array[4]; array[4] = temp; Value 23 45 7 33 78 Index 1 2 3 4 5

Class public class Circle { private int point; private int radius; public Circle( int newPoint, int newRadius ) { point = newPoint; radius = newRadius; } public int getLocation() { return point; } public void setLocation( int newPoint) { point = newPoint; }

Class (cont’d.) public int getRadius() { return radius; } public void setRadius( int newRadius ) { radius = newRadius; } public double getPerimeter() { return 2 * Math.PI * radius; } public double getArea() { return Math.PI * radius * radius; } public String toString() { return "The point is " + point + "\nThe radius is " + radius + "\nPerimeter of the circle is " + getPerimeter() + "\nArea of the circle is " + getArea();

Client Class public class ClientCircle { public static void main( String [] args ) { Circle circ = new Circle( 4, 5 ); System.out.println( circ.toString() ); } } The point is 4 The radius is 5 Perimeter of the circle is 31.41592653589793 Area of the circle is 78.53981633974483

Bibliography Anderson, Julie and Franceschi, Herve. Java Illuminated.