In this chapter, the following content will be discussed: Introduce to classes and objects in Java, understand how some of the OO concepts learnt so far are supported in Java, understand important features in Java classes. | Software Construction Lab 3 Classes and Objects in Java Basics of Classes in Java Contents Introduce to classes and objects in Java. Understand how some of the OO concepts learnt so far are supported in Java. Understand important features in Java classes. Classes A class is a collection of fields (data) and methods (procedure or function) that operate on that data. Circle centre radius circumference() area() Classes A class is a collection of fields (data) and methods (procedure or function) that operate on that data. The basic syntax for a class definition: Bare bone class – no fields, no methods public class Circle { // my circle class } class ClassName [extends SuperClassName] { [fields declaration] [methods declaration] } Adding Fields: Class Circle with fields Add fields The fields (data) are also called the instance varaibles. public class Circle { public double x, y; // centre coordinate public double r; // radius of the circle } Adding Methods A class . | Software Construction Lab 3 Classes and Objects in Java Basics of Classes in Java Contents Introduce to classes and objects in Java. Understand how some of the OO concepts learnt so far are supported in Java. Understand important features in Java classes. Classes A class is a collection of fields (data) and methods (procedure or function) that operate on that data. Circle centre radius circumference() area() Classes A class is a collection of fields (data) and methods (procedure or function) that operate on that data. The basic syntax for a class definition: Bare bone class – no fields, no methods public class Circle { // my circle class } class ClassName [extends SuperClassName] { [fields declaration] [methods declaration] } Adding Fields: Class Circle with fields Add fields The fields (data) are also called the instance varaibles. public class Circle { public double x, y; // centre coordinate public double r; // radius of the circle } Adding Methods A class with only data fields has no life. Objects created by such a class cannot respond to any messages. Methods are declared inside the body of the class but immediately after the declaration of data fields. The general form of a method declaration is: type MethodName (parameter-list) { Method-body; } Adding Methods to Class Circle public class Circle { public double x, y; // centre of the circle public double r; // radius of circle //Methods to return circumference and area public double circumference() { return 2**r; } public double area() { return * r * r; } } Method Body Data Abstraction Declare the Circle class, have created a new data type – Data Abstraction Can define variables (objects) of that type: Circle aCircle; Circle bCircle; Class of Circle cont. aCircle, bCircle simply refers to a Circle object, not an object itself. aCircle Points to nothing (Null Reference) bCircle Points to nothing (Null Reference) null null Creating objects of a class Objects are
