What is a Class in Java
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 Animal.
- 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
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) { … }
}
Object
Real world objects are things that have:
- state
- behavior
Example: your dog:
state –name, color, breed, sits?, barks?, wages tail?, runs?
behavior –sitting, barking, waging tail, running
A software object is a bundle of variables (state) and methods (operations).
Object Creation:
A variable is declared to refer to the objects of type/class String:
String s;
The value of s is null; it does not yet refer to any object.
A new String object is created in memory with initial “abc” value:
String s = new String(“abc”);
Now s contains the address of this new object.
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);
}
}
Example for class
class sum
{
int a,b,sum;
void get()
{
a=10;b=5;
}
void sum()
{
sum=a+b;
//System.out.print("sum is "+sum);
}
}
class sum1
{
public static void main(String args[])
{
sum s1=new sum();
s1.get();
s1.sum();
System.out.print("sum is" +s1.sum);
}