Java Defining Class
Let's consider a scenario Car as a class (template). It has properties such as a model, color, and year. It has methods such us gear(),stop() and brake(). Objects represent the class. Hence car1, car2, and car3 are the objects of class Car.
.png)
A class is a group of objects which have common properties. It is a user-defined data type with a template that serves to define its properties. To create a class, use the keyword class.
A class can contain any of the following variable types.
- Local variables − Variables defined inside methods, or blocks are called local variables. Methods are used to perform certain actions, and they are also known as functions.
int area()
{
int length = 10; //local variable
int breadth = 5; //local variable
int rectarea = length*breadth; //local variable
return rectarea;
}
- Instance variables − Instance variables are variables within a class but outside any method.
class Student
{
int rollno;// rollno is an Instance variable
void details(){
}
}
- Class variables − Class variables are variables declared within a class, outside any method, with the static keyword. Keywords are reserved words.
class Student
{
static int rollno;// rollno is class variable
void details(){
}
}
Defining a Class:
Class consists of field declarations and method declarations.
.png)
Syntax:
class classname {
field declaration;
method declaration;
}
Example:
class Student { // Student is the classname
// state or field declaration
String name = "Anu";
int mark1 = 50;
int mark2 = 70;
int mark3 = 60;
// behavior or method declaration
void total() {
System.out.println("Total");
}
void average() {
System.out.println("Average");
}}
The variables and methods of the class are embraced by the curly brackets that begin and end the class definition block.
i) Fields Declaration:
A Java field is a variable. This means that it represents a value, such as a numerical value or a text.
syntax:
class classname{
type fieldname;
}
Example:
class Student{
String name ="Anu"
int mark1 = 50;
int mark2 = 70;
int mark3 = 60;
}
/* name, mark1, mark2 and mark3 are the fields declared inside the class Student
ii) Method Declaration:
A Java method is a function. It's a block of code that carries out an operation. Like Java fields, Java methods must be declared inside classes. A Java method can accept values from fields and return results back to other parts of the program.
syntax:
type methodname( parameter-list ){
method-body;
}
Example:
void total() {
System.out.println("Total");
}
void average() {
System.out.println("Average");
}
/*total() and average() are the methods