Static keyword ppt

Static
Compiled By:
Vinod Kumar(Asst. Prof.)

Java 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.
• Java supports definition of global methods and variables that can be
accessed without creating objects of a class. Such members are called Static
members.
• Define a variable by marking with the static methods.
• This feature is useful when we want to create a variable common to all
instances of a class.
• Note: Java creates only one copy for a static variable which can be used
even if the class is never instantiated.
The static can be:
• variable (also known as class variable)
• method (also known as class method)
• block
• nested class

3
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).
class Student{
int rollno;
String name;
String university=“CURAJ";
}
Suppose there are 2000 students in our university, 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, university refers to the common
property of all objects . If we make it static , this field will get memory only once.

Example 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();
}
}

Program of counter without static variable and by
static variable
without static variable
class Counter{
int count=0;/*will get memory when instance is c
reated */
Counter(){
count++;
System.out.println(count);
}
Counter c1=new Counter();
}
}
By static variable
class Counter2{
static int count=0;/*will get memory only once an
d retain its value */
Counter2(){
count++;
System.out.println(count);
}
Counter2 c1=new Counter2();
}
}

6
Static Methods
• A static method belongs to the class rather than object of
a class.
• A class can have methods that are defined as static (e.g.,
main method).
• Static methods can be accessed without using objects.
Also, there is NO need to create objects.
• static method can access static data member and can
change the value of it.
• They are prefixed with keyword “static”
• Static methods are generally used to group related library
functions that don’t depend on data members of its class.
For example, Math library functions.

Example :1
class Student9{
int rollno;
String name;
static String university = "ITS";
static void change(){
university = “Curaj";
}
Student9(int r, String n){
rollno = r;
name = n;
}
void display ()
{
System.out.println(rollno+" "+name+" "+university);
}
Student9.change();
Student9 s1 = new Student9 (111,"Karan");
Student9 s2 = new Student9 (222,"Aryan");
Student9 s3 = new Student9 (333,"Sonoo");
s1.display();
s2.display();
s3.display();
}
}
Output:-
111 Karan Curaj
222 Aryan Curaj
333 Sonoo Curaj

Example: 2
class Calculate{
static int cube(int x){
return x*x*x;
}
int result=Calculate.cube(5);
System.out.println(result);
}
}
Output :
125

Comparator class with Static methods
/* Comparator.java: A class with static data
items comparison methods*/
class Comparator {
public static int max(int a, int b)
{
if( a > b)
return a;
else
return b;
}
public static String max(String a, String b)
{
if( a.compareTo (b) > 0)
return a;
else
return b;
}
}
class MyClass {
public static void main(String args[])
{
String s1 = "Melbourne";
String s2 = "Sydney";
String s3 = "Adelaide";
int a = 10;
int b = 20;
System.out.println(Comparator.max(a, b));
// which number is big
System.out.println(Comparator.max(s1, s2));
// which city is big
System.out.println(Comparator.max(s1, s3));
// which city is big
}
}
9
Directly accessed using
ClassName (NO Objects)

10
Static methods restrictions
• They can only call other static methods.
• They can only access static data.
• They cannot refer to “this” or “super” (more later) in anyway.
class A2{
static{System.out.println("static block is invoked");}
System.out.println("Hello main");
}
}
Output:
static block is invoked
Hello main

Can we execute a program without
main() method?

• Yes, one of the way is static block but in previous version of
JDK not In JDK 1.7.
class A3{
static{
System.out.println("static block is invoked");
System.exit(0);
}
}

Static keyword ppt

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Static keyword ppt