Variables in Java

 

Types of Variables

A. Based on the type of volume

1. Primitive Variables

    int x = 10;
   

2. Reference Variables

    Student s = new Student ();
   

B. Based on the position od declaration or behaviour

1. Instance Variable

    class Student{
        String name;
        int rollNo;
    }
   
    name = "Nishal"  // Student One
    rollNo = 20;
   
    name = "Biswas"  // Kukur One
    rollNo = 8;
   

• For every object separate copy of name and rollno is created. This type of variable is instanec variable.
• Instance variable are declared within a class and outside of method / block / constructor.
• Instance variable are created at the time of object creation and destroy when object is destroyed.
• They are also known as attributes.

2. Static Variable

• If the value of variable is not variet from object to object , we create static variable

    class Student{
        static Sting name;
    }
  
    name = "Nishal" // Student One; Student Two
  

• Are declared inside class but outside of any method / block / constructor.

  • Scope
    ⏩ Created at the time of class loading and destroyed at the time of class unloading.

3. Local Variable

    [method]
    void mOne{
        int x = 10; // is not available outside for loop.
    }
   
    [block]
    for(int i = 0; i<5; i++){
        System.out.println(i); // is not available outside for loop.
    }
   
    [constructor]
    Test(){
        int x = 10;
    }
   

• aka Local / Temporary / Stack / Automatic
• are stored in stack memory.
• Scope : ⏩ Destroy after finishing method / block / constructor
• for every thread separate, local variable is created.
• For local variable, JVM won't provide default value. So, we must provide value explicitly before using it.
• For local variable, the only applicable modifier is final.