Variables in Java

    A variable is a container which holds the value while the Java program is executed. A variable is assigned with a data type.

Variable is a name of memory location. There are three types of variables in java: local, instance and static.

There are two types of data types in Java: primitive and non-primitive.

• Local variable

- A local variable is declared inside a method, constructor, or block.
- It can be used only within the scope where it is declared.
- A local variable must be initialized before you use it.
- A local variable does not have a default value.
- It is created when the method/block is executed and becomes unavailable when the execution leaves that scope.
- A local variable cannot be declared with static.
- A local variable can have the same name as an instance variable (this is called shadowing).
- Local variables are generally stored in the stack frame of the executing method.

• Instance variable

- An instance variable is declared inside a class but outside any method, constructor, or block.
- It is not declared with the static keyword.
- Each object (instance) of the class has its own separate copy of the instance variable.
-Its value can be different for each object.
- It is created when an object is created and normally exists as long as the object exists.
- Instance variables have default values if you don't initialize them.
- Instance variables can be accessed by instance methods.
- They are stored as part of the object in the Heap.

- They can have access modifiers such as private, public, or protected.

• Static variable

   

- A variable declared with the static keyword is called a static variable.
- A static variable is declared inside a class but outside methods, constructors, or blocks.
- It cannot be a local variable.
- There is only one copy of a static variable for the entire class.
- The same static variable is shared by all objects (instances) of the class.
- Changing the static variable through one object affects the value seen by other objects.
- A static variable can be accessed using the class name, without creating an object.
- Static variables have default values if they are not explicitly initialized.
- Static variables are associated with the class, not with individual objects.
- Static variables are initialized when the class is initialized by the JVM.

public class VariableExample {

// Static variable

private static int staticVar;

// Instance variable

private int instanceVar;

public void someMethod() {

// Local variable

int localVar = 42;

// Using variables

System.out.println("Static Variable: " + staticVar);

System.out.println("Instance Variable: " + instanceVar);

System.out.println("Local Variable: " + localVar);

}

public static void main(String[] args) {

// Accessing static variable

staticVar = 10;

// Creating an instance of the class

VariableExample obj = new VariableExample();

// Accessing instance variable

obj.instanceVar = 20;

// Calling a method that uses local variable

obj.someMethod();

}

}