What is a Class?
• A class is a blueprint that defines the variables and methods common to all objects of a certain kind.
• Example: ‘your dog’ is a object of the class Dog.
• An object holds values for the variables defines in the class.
• An object is called an instance of the Class.
• A basis for the Java language.
• Each concept we wish to describe in Java must be included inside a class.
• A class defines a new data type, whose values are objects:
• A class is a template for objects
• An object is an instance of a class
Class Definition
A class contains a name, several variable declarations (instance
variables) and several method declarations. All are called
members of the class.
General form of a class:
class classname {
type instance-variable-1;
...
type instance-variable-n;
type method-name-1(parameter-list) { ... }
type method-name-2(parameter-list) { ... }
...
type method-name-m(parameter-list) { ... }
}
Example: Class Usage
class Box {
double width;
double height;
double depth;
}
class BoxDemo {
public static void main(String args[]) {
Box mybox = new Box();
double vol;
mybox.width = 10;
mybox.height = 20;
mybox.depth = 15;
vol = mybox.width * mybox.height * mybox.depth;
System.out.println ("Volume is " + vol);
} }