Object-Oriented Programming Concepts

• Object-oriented programming (OOP) uses objects that belong to specific classes to solve programming problems.
• Each object is a self-contained entity.
• Objects possess properties (fields) and actions (methods).
• A class serves as a blueprint, defining the behavior of objects created from it.
• An object from the Triangle class will have different properties and actions than an object from a Rectangle class.
• An instance of a class is an object created from that class.
• Instantiation refers to the process of creating an object from a class
• A class can be used to produce multiple objects.
• Encapsulation combines methods and fields into a single unit within a class
• Encapsulation happens when fields and methods combine into one unit within a class.
• Static fields and methods are used to program a class without needing to create objects of that class.
• Method overloading refers to the ability of two methods to share a name.
• Method signature refers to the way a method is identified, using its name and its parameter set.
• Method resolution is the process of identifying a method when two methods share a name, through the parameter set.

Typed vs. Void Methods

• A typed method returns a value to the call statement.
• A void method performs an action, like changing a field's value or producing output, but does not return a value.

Static vs. Non-Static

• Static methods are associated with a class and do not require object instantiation.
• The Math class methods, Character class methods are examples of Static methods.
• You must instantiate a class object for non-static methods.
• String objects are examples of non-static methods.

User-Defined Methods (Triangle Class)

• User defined static methods must use the "static" keyword.
• Example: public static void/type methodName(parameters)
• User defined non static methods do not need to use to use the "non-static" keyword.
• Example: public void/type methodName(parameters)

Non-Static Class Structure

• Non-static classes typically include a package declaration.
• Example: package myTriangle;
• Often include import statements
• Example: import javax.swing;
• Class declarations must be declared as public or protected, but not private.
• Class declarations must include the name of the class
• Example: public class Triangle
• Classes specify a list of fields with public, private, or protected access.
• Example: public int width=0; or private int width;
• Public fields need an initial value.
• Private fields need getter and setter methods.
• Classes include constructor methods like default and/or parameterised constructors.
• Constructor methods are not needed if the fields are public
• Getter and setter methods are used for private fields.
• Methods can be typed or void, and may include parameters, supporting IPO programming.
• Method overloading happens when two methods share a name.

Calling from Classes with main Method

• Instantiating an object is done using ClassName ObjectName = new ClassName();.
• If you are creating a new Triangle object, you would use Triangle tri = new Triangle();.
• Public fields can be accessed using ObjectName.FieldName;.
• tri.width = 5; is an example of accessing the width of the triangle object.
• Getter and setter methods are used to call private variables.
• Example: tri.setWidth(5);
• Public methods are called using ObjectName.MethodName();.
• Example: double area = tri.calcArea();

Programming w/Private Fields (Triangle Example)

• Private fields need to be declared
• Example: private int width;
• Default constructors assign default values to fields.
• Parameterised constructors assign supplied values to fields.
• Setter methods are void, receiving a value, and storing it in the formal parameter.
• Getter methods are typed, passing the field's value back to the call statement.
• Other methods perform calculations or actions.
• Named public methods can declare the calculations.
• Example public double calcArea() or public void multiplyWidth( int m)

Void Method Call Notes From Triangle Object

• Instance of triangle is created Triangle tri = new Triangle();
• Void methods do not need to be stored, as nothing is sent back.
• Actual parameters (values) need to be sent in parameterised methods.
• Example statements:
  • tri.setWidth(5);
  • tri.setHeight(10);

Typed Method Call Notes From Triangle Object

• Typed methods require storage of sent-back data through assignment or as part of another statement.
• Call statement with no parameter sent in. -double area = tri.calcArea();
• The output of printed width, height and area of tri object.
• System.out.println( "The width is " +tri.getWidth()+ "\nThe height is " +tri.getHeight()+ “\nThe area is " +area);

Public Field Programming (Triangle Example)

• Classes with public fields do not need constructors due to parameters being known
• Named public methods can declare the calculations.
• Example public double calcArea() or public void multiplyWidth( int m)
• New instance of triangle is created
• Triangle tri = new Triangle();
• The width for the new object can be declared directly
• tri. width = 5;
• The output of printed width, height and area of tri object.
• System.out.println( "The width is " +tri. width + “\nThe height is " +tri. height + “\nThe area is " +area);

Explore object-oriented programming (OOP) with objects, classes, and instances. Understand encapsulation, static methods, and method overloading. Learn how classes act as blueprints for creating objects with unique properties and actions.