Variables in Java

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Java is an object-oriented programming language that uses variables to store data. In this post, we will discuss the different types of variables in Java: local variables, instance variables, and static or class variables.

Local Variable

Local variables are defined within a method and can only be accessed within that method. They do not have a default value and must be initialized before use. Here is an example of a local variable in Java:

public class LocalVariableExample {
   public static void main(String[] args) {
      int age; // local variable
      age = 25;
      System.out.println("My age is: " + age);
   }
}

Output:

My age is: 25

Instance Variable

Instance variables, also known as member variables, are defined within a class but outside of any method. They are associated with an object of that class and have a default value of null. Here is an example of an instance variable in Java:

public class InstanceVariableExample {
   // instance variable
   String name;

   public static void main(String[] args) {
      InstanceVariableExample obj = new InstanceVariableExample();
      System.out.println("My name is: " + obj.name);
   }
}

Output:

My name is: null

Static Variable

Static or class variables are defined within a class and outside of any method, but have the ‘static’ keyword before their data type. They are associated with the class, not an object, and have a default value of 0. Here is an example of a static variable in Java:

public class StaticVariableExample {
   // static variable
   static int count = 0;

   public static void main(String[] args) {
      StaticVariableExample obj1 = new StaticVariableExample();
      obj1.count++;
      StaticVariableExample obj2 = new StaticVariableExample();
      obj2.count++;
      StaticVariableExample obj3 = new StaticVariableExample();
      obj3.count++;
      System.out.println("Total objects created: " + count);
   }
}

Output:

Total objects created: 3

Conclusion

Variables are used to store data in Java. Local variables are defined within a method, instance variables are defined within a class, and static variables are defined within a class and shared among all objects. It’s important to understand the difference between these variable types to write efficient and effective Java code.

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