Static Keyword
The static
keyword is is used
for memory management . java static keyword can be used with a variables
, methods , blocks and nested class. When we define a static keyword with
method and varriable then it is related to class.
The
static can be:
- A
class member (varriable)
- A
method of class
- A
block
- A
nested class (class within class)
1) Java static variable
Static varriable are those varriable which are related to class
instead of objects .
Static varriable gets the memory once at time of class loading not at the time of object creation .
Advantage of static variable
static is used for efficient utilization of memory.
Understanding problem
without static variable
class Employee
{
int Eid;
String name;
String company="google";
}
Let us assume there are 10,000
employee`s in company , now all data
members of class get memory each time
when object of class is created. All employye`s
have its unique Eid and name so i should
not be static because it is related to every employee but company name is common for all employees . If we make company
name static than it takes memory only
once
Example of static variable
//Program of static variable
class employee{
int eid;
String name;
static String company ="google";
employee(int a,String b){
eid = a;
name = b;
}
void display ()
{
System.out.println(eid+" "+name+" "+company);}
public static void main(String args[])
{
employee
e1 = new employee(1200,"vinay");
employee
e2 = new employee(1201,"abhishek");
s1.display();
s2.display();
}
}
class Javacount {
int i=0;// i gets the memory when object of a
class is created
Javacount(){
i++;
System.out.println(i);
}
public static void main(String a[]){
Javacount
c1=new Javacount
();
Javacount
c2=new Javacount
();
Javacount
c3=new Javacount
();
}
}
Output:1
1
1
class Javacount {
static int i=0;// i gets the memory when object of a
class is created
Javacount(){
i++;
System.out.println(i);
}
public static void main(String a[]){
Javacount
c1=new Javacount
();
Javacount
c2=new Javacount
();
Javacount
c3=new Javacount
();
}
}
Output:1
2
3
Where static method can’t be used
1. static
method is not able to acces non static data members and non static method.
2. In static method this and super keyword is not
used .
1.
class employee{
2.
int value=40; //
non static data member
3.
4.
public static void main(String a[]){
5.
System.out.println(value);
6.
}
7.
}
Output:Compile Time Error
Java static block
- static
block is used for static data member initialization .
- static
block executed before the main method .
Example of static block
1.
class employee
2.
{
3.
Static
4.
{
5.
System.out.println("this is static block of employee class");}
6.
7.
public static void main(String argument[])
8.
{
9.
10. System.out.println("main funtion is invoked ");
11.
12. }
13. }
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