static keyword
The static keyword in java is used for memory management mainly. We can apply java static keyword with variables, methods, blocks and nested class. The static keyword belongs to the class than instance of the class.
The static can be:
Java static variable
If you declare any variable as static, it is known static variable.
Advantage of static variable
It makes your program memory efficient (i.e it saves memory).
Understanding problem without static variable
class Student
{
int rollno;
String name;
String college="ITS";
}
Suppose there are 500 students in my college, now all instance data members will get memory each time when object is created.All student have its unique rollno and name so instance data member is good.Here, college refers to the common property of all objects.If we make it static,this field will get memory only once.
Example of static variable//Program of static variable
class Student8{
int rollno;
String name;
static String college ="ITS";
Student8(int r,String n){
rollno = r;
name = n;
}
void display (){System.out.println(rollno+" "+name+" "+college);}
public static void main(String args[]){
Student8 s1 = new Student8(111,"Karan");
Student8 s2 = new Student8(222,"Aryan");
s1.display();
s2.display();
}
}
Output:111 Karan ITS 222 Aryan ITS
Java static method
If you apply static keyword with any method, it is known as static method.
Why java main method is static?
Because object is not required to call static method if it were non-static method, jvm create object first then call main() method that will lead the problem of extra memory allocation.
What is difference between static (class) method and instance method?
static or class method instance method
1) A method i.e. declared as static is known as static method A method i.e. not declared as static is known as instance method.
2) Object is not required to call static method. Object is required to call instance methods.
3) Non-static (instance) members cannot be accessed in static directly.static and non-static variables both can be accessed in instance context (static method, static block and static nested class) methods.
The static can be:
- variable (also known as class variable)
- method (also known as class method)
- block
- nested class
Java static variable
If you declare any variable as static, it is known static variable.
- The static variable can be used to refer the common property of all objects (that is not unique for each object) e.g. company name of employees,college name of students etc.
- The static variable gets memory only once in class area at the time of class loading.
Advantage of static variable
It makes your program memory efficient (i.e it saves memory).
Understanding problem without static variable
class Student
{
int rollno;
String name;
String college="ITS";
}
Suppose there are 500 students in my college, now all instance data members will get memory each time when object is created.All student have its unique rollno and name so instance data member is good.Here, college refers to the common property of all objects.If we make it static,this field will get memory only once.
Example of static variable//Program of static variable
class Student8{
int rollno;
String name;
static String college ="ITS";
Student8(int r,String n){
rollno = r;
name = n;
}
void display (){System.out.println(rollno+" "+name+" "+college);}
public static void main(String args[]){
Student8 s1 = new Student8(111,"Karan");
Student8 s2 = new Student8(222,"Aryan");
s1.display();
s2.display();
}
}
Output:111 Karan ITS 222 Aryan ITS
Java static method
If you apply static keyword with any method, it is known as static method.
- A static method belongs to the class rather than object of a class.
- A static method can be invoked without the need for creating an instance of a class.
- static method can access static data member and can change the value of it.
Why java main method is static?
Because object is not required to call static method if it were non-static method, jvm create object first then call main() method that will lead the problem of extra memory allocation.
What is difference between static (class) method and instance method?
static or class method instance method
1) A method i.e. declared as static is known as static method A method i.e. not declared as static is known as instance method.
2) Object is not required to call static method. Object is required to call instance methods.
3) Non-static (instance) members cannot be accessed in static directly.static and non-static variables both can be accessed in instance context (static method, static block and static nested class) methods.