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Java Programming Types Of Variables

Types of Variables:

  • Local
  • Instance
  • Transient
  • Volatile
  • Static
  • Final

What is Local Variable?

The variables created inside a method or block are called local variables.

Local variables can not be accessed from another method. Because its scope is restricted only within its method.

Example

package easy;
class test{
 public void show(){
 System.out.println("a:"+a); //Compile time error: cannot find symbol a.
}
 public static void main(String [] args){
 int a=10;
 System.out.println("a:"+a);
   }
}
Try it Yourself

What is Instance variables?

Instance variable gets life when object is created. It is destroyed when object is destroyed.

Object is destroyed when it is unreferenced.

Its scope is the scope of the object, object is available only if its referenced variable is available

Example

package easy;
class test{
 int a=10;
public static void main(String [] args){
test t= new test();
System.out.println("a:"+t.a);

  }
}
Try it Yourself

What is Transient variable?

The class level variable that has transient keyword in its definition is called transient variable.

Local variable can not be declared as transient.

It leads to Compile time error: Illegal start expression

Example

package easy;
class test{
static transient int a=10;
static transient  int b=20;
public static void main(String [] args){
transient int x=10; // compile time error : illegal start expression
  }
}
Try it Yourself

We declare variable as transient to tell to JVM that we do not want to store variable value in a file in object serialization. Since local variable is not part of object , declaring it as transient is illegal.

What is Volatile Variable?

The class level variable that has volatile keyword in its definition.

Local variable can not be declared as volatile.

It leads to Compile time error: Illegal start expression

Example

package easy;
class test{
static volatile int a=10;
volatile int b=20;
public static void main(String [] args){
 volatile int x=10; // compile time error : illegal start expression
 }
}
Try it Yourself

We declare variable as volatile to tell to JVM that we do not want to modify variable value concurrently by multiple threads.

If we declare variable as volatile multiple threads are allowed to change its value in sequence one after another one.

Note:We learn about static and final keywords shortly.

Solve this!!

13986.What is the output of this program? 
double FLOAT = 2.5 ;
System.out.println(  FLOAT );
2.5
Rraises an error as FLOAT is used as a variable which is a keyword
0
None of these
13987.What is the output of this program? 
    class variable_scope {
        public static void main(String args[]){
            int x;
            x = 5;
            {
	        int y = 6;
	        System.out.print(x + " " + y);
            }
            System.out.println(x + " " + y);
        } 
    }
5
6
0
Error
Explanation:
Second print statement doesn’t have access to y , scope y was limited to the block defined after initialization of x. Exception in thread “main” java.lang.Error: Unresolved compilation problem: y cannot be resolved to a variable
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