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In this lecture we are discussing:
1)What is use static keyword in java? (discussed in static variable lecture)
2)At which place we can use static keyword.
3)when memory get allocated (discussed in static variable lecture)
4)static variable vs instance variable(discussed in static variable lecture)
5)static block vs non static method (discussed in static block lecture)
6)static method vs non static method (discussed in this lecture)

#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

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


//instance
System.out.println(obj1.inB); // output: 1000
System.out.println(obj2.inB); // output: 100 no change in obj2
}
}

#5
static block vs non static block
= remember static block executed before the execution of static method
= non static block executed when you try to create the object and executed before constructor called.

class Calc{
static{
System.out.println("Static Block");
System.out.println("Executed before main");
}

{
//non static block
System.out.println("Non static block executed before the execution of constructor");
}

public static void main(String []args){
System.out.println("main method");
Calc c = new Calc(); //non static block executed when we create object
// Help h ; -- this will not execute static block of Help class
// Help h = new Help(); this will execute static block of Help class
Help.wish(); //-- this will execute static block of Help class

}
}

class Help{
static {
System.out.println("Static block of Help class");
}
static void wish(){
System.out.println("Hello");
}
}

/*
PS D:\telusko\january\java-course-telusko\code javac Calc.java
PS D:\telusko\january\java-course-telusko\code java Calc
Static Block
Executed before main
main method
Non static block executed before the execution of constructor
Static block of Help class
Hello
*/

#6
Static method vs non static method
= remember we can call static method with object reference or class name e.g ClassName.staticMethod() or objReference.statiMethod()
= but non static method dependent on object so it can be called only by object reference. e.g objReference.nonStaticMethod();

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.

Github repo : https://github.com/navinreddy20/Javacode.git