Types of variables

Types of Variables in Java

In Java, variables are containers for storing data values. They can be classified into three types based on their scope and lifetime:

• Local variables: These variables are declared within a method, constructor, or block and have local scope. They are accessible only within the enclosing block and cease to exist once the block is exited.
• Instance variables: These variables are declared within a class but outside any method. They have instance scope and are associated with an instance of the class. They exist as long as the instance of the class exists.
• Static variables: These variables are declared with the static keyword within a class. They have class scope and are associated with the class itself, not with any instance. They are created when the class is loaded and remain in memory until the program terminates.

Here's an example to illustrate the types of variables:

    
      public class VariableExample {
        // Instance variable
        private int instanceVariable;
        
        // Static variable
        private static String staticVariable;
        
        public void exampleMethod() {
          // Local variable
          int localVar = 10;
          
          // Code using the variables...
        }
      }
    
  

The following diagram illustrates the relationship between the types of variables in Java:

Instance Variable

→

Instance of Class

→

Local Variable

Static Variable

→

Class

Here's a brief summary of the types of variables:

Type	Scope	Lifetime
Local Variable	Within a method, constructor, or block	Created when the block is entered, destroyed when the block is exited
Instance Variable	Within a class, but outside any method	Created when an instance of the class is created, destroyed when the instance is garbage collected
Static Variable	Within a class, declared with the static keyword	Created when the class is loaded, destroyed when the program terminates

Conclusions:
1) For the static and instance variables it is not required to perform initialization explicitly JVM will provide default values. But for the local variables JVM won’t provide any default values compulsory we should perform initialization explicitly before using that variable.
2) For every object a separate copy of instance variable will be created whereas for entire class a single copy of static variable will be created. For every Thread a separate copy of local variable will be created.
3) Instance and static variables can be accessed by multiple Threads simultaneously and hence these are not Thread safe but local variables can be accessed by only one Thread at a time and hence local variables are Thread safe.

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