Class is the means by which you define objects. A class may contain three types of items : variables, methods and constructors.
Variables represent its state. Class can have static and instance variables. Methods provide the logic that constitutes the behavior defined by a class. Class can have static and instance methods. Constructors initialize the state of a new instance of a class.
General form or Syntax of a Class
class clsName
{
// instance variable declaration
type1 varName1 = value1;
type2 varName2 = value2;
:
:
typeN varNameN = valueN;
// Constructors
clsName(cparam1)
{
// body of constructor
}
:
:
clsName(cparamN)
{
// body of constructor
}
// Methods
rType1 methodName1(mParams1)
{
// body of method
}
:
:
rTypeN methodNameN(mParamsN)
{
// body of method
}
class indicates that a class named clsName is being declared. It must follow the java naming conventions for identifiers.
Instance variables named varName1 through varNameN are normal variable declaration syntax. Each variable must be assigned a type shown as type1 through typeN and may be initialized to a value shown as valueN.
Constructors always have the same name as the class. They do not have return values. cparam1 through cparamN are optional parameter lists.
Methods named mthName1 through mthNameN can be included. The return type of the methods are rtype1 through rTypeN and mParamN aew an optional parameter lists.
Example of a General Class
class clsSample
{
// Variables
static int ctr;
int i;
int j;
// Constructor
clsSample()
{
ctr = 0;
i = 0;
j = 0;
}
clsSample(int a, int b, int c)
{
ctr = a;
i = b;
j = c;
}
// Methods
int addition()
{
ctr++;
return i + j;
}
int NumberOfInstances()
{
return ctr;
}
}
Creating Object of clsSample Class
clsSample smpObj = new clsSample();