#37 Static Variable in Java

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In this lecture we are discussing:
1)What is use static keyword in java?
2)At which place we can use static keyword. (discussing in upcoming next video)
3)when memory get allocated (extra information how static variable memory get allocated)
4)static variable vs instance method
#1
Use of static keyword
= when we are using static keyword with variable, block, method it become
independent of object.
e.g class{
static int a=5;
}
= a is not dependent on object .if we have two object obj1 and obj2 then both object able to access this
variable.
= when we are using static it become independent to object.
#2
Four place we can use static keyword
a) before variable declaration e.g class Calc{ static int s; }
b) before a block class Calc{ static {System.out.println("this is static block);}}
c) during method creation class Calc{public static void add(int num1,int num2){};}
d) with concept of inner class (It is not discussed in this lecture)
class OuterClass {
int x = 10;
static class InnerClass {
int y = 5;
}
}
#3
When memory get allocated
= for that we need to know some term
a)stack area b)heap area c)class loader system
Step 1: when you compile the code you get .class file
Step 2: when you are executing (java MainClass) first class loading to class loader System.
Step 3: During class loading static variable initialize, static block get executed.
Step 4: Since, static variable got memory in heap before object creation. Now we can say that it is independent of object.
#4
Static variable vs instance variable
Class Calc{
static int stA=100; //independent of object // we can use this by class name as well as object
int inB=100; //dependent of object //we can only use this by object
public static void main(String []args){
Calc obj1=new Calc();
Calc obj1=new Calc();
//for static variable
System.out.println(Calc.stA); //use with class name
System.out.println(obj1.stA); //use by object name
//for instance variable
//System.out.println(Calc.inB); //got an error --Cannot make a static reference to the non-static
System.out.println(obj1.inB); //used by object name reference
// = if we can change value static or instance what happen
obj1.inB=1000;
obj1.stA=2000;
//static
System.out.println(obj1.stA);//output: 2000
System.out.println(obj2.stA);//output: 2000 value changed for both obj1 and obj2
//it also show that static variable independent of objects
//instance
System.out.println(obj1.inB); // output: 1000
System.out.println(obj2.inB); // output: 100 no change in obj2
}
}
Remember one thing:
i)we can use static property, member inside non static block or method without object creation.
ii) But we cannot use non static property or method inside static block or method without object creation.
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[@MdRahaman-pj9rc]

Your explanation of static variable helps to understand static keywords better. Thanks.

[@sarthaknema1130]

Can I say a static variable is like a global variable? So local variables can only be shared/used among the instance/object. But a global variable can be used by the entire class and every instance/object belonging to that class?

[@ahmadwaheed8003]

Great explanation

[@zobaidullahniazmand4375]

thanks dear theacer your Student from Afghanistan

[@user-nd7pw9gc1w]

nice explanation sir

[@spiderman699]

Well explained 🎉❤

[@vanvietngo4217]

Very helpful ! When creating the variable static name, you said that the name property of obj1 and obj2 will share the same static name, the static name is stored in an area in the heap memory, then the name attribute of obj1 and the name attribute of obj2 are in memory heap will contain the address of the static name in the heap memory right?

[@MoeMoe-qr7od]

excellent explain static

[@Divyasri1922]

Well explanation

[@nitinanand3408]

By the way price of an apple is lower than price of samsung... Must throw an error

[@MoeMoe-qr7od]

wkwk

[@ashwintate1009]

But when we access static variable with object ref then we can change the value of static variable for all the objects then how its maintain rule of common for all (Belong to class ) or its just behaves like instance variable with hard core value ???? Is Memory saving the only difference ???

[@ahmadwaheed8003]

Yes we can access with object reference but it will reflect in all the objects so it is called common area.

[@ahmadwaheed8003]

Yes when we make a common variable for all the objects we don't need to initialize it with each object so memory saving is the advantage of using static.

[@swethasenthilkumar6372]

Sir I had an interview yesterday what is the significance of static variable .I don't know can you explain

[@alinakhan1159]

less memory is used for instance if you declare 3 non static integer variables then each object will occupy 12 bytes of memory ..if there are 3 objects total will be 36 but if you declare one static variable and if the other 2 are non static then static variable will take its 4 bytes which will be shared with all objects and each object will separately take its 8 bytes of storage..so total memory that is used for 3 objects will be 24 bytes and 24+4 is 28 bytes...

[@preyas2198]

Sir where the static variable is stored ?? Inside stack memory or Heap memory ?

[@neerajgarg9096]

heap memory

[@Nikita-qc7dp]

Inside static nd global memory of heap

[@puruagni1927]

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