Java Variable

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Java Variable

In this tutorial, you will learn what is Java variable and how to work with it. Also, you will learn where variables are commonly used in Java programming.

A variable or Java Variable provides us with named storage that our programs can manipulate. Each variable in Java has a specific type, which determines the size and layout of the variable’s memory; the range of values that can be stored within that memory; and the set of operations that can be applied to the variable.

In simple Words, it can Be defined as “Variable is the name of the reserved area allocated in memory.”

You must declare all variables before they can be used. Following is the basic form of a variable declaration −

data type variable [ = value][, variable [ = value] ...] ;

Here data type is one of Java’s datatypes and variable is the name of the variable. To declare more than one variable of the specified type, you can use a comma-separated list.

Below given is valid examples of variable declaration and initialization in Java −

variable declaration and initialization

int a, b, c;         // Declares three ints, a, b, and c.
int a = 10, b = 10;  // Example of initialization
byte B = 22;         // initializes a byte type variable B.
double pi = 3.14159; // declares and assigns a value of PI.
char a = 'a';        // the char variable a iis initialized with value 'a'

Types of variables:

  • local variable
  • instance variable
  • static variable

Local Java variable

  • Local variables are declared in methods, constructors, or blocks.
  • Local variables are created when the method, constructor or block is entered and the variable will be destroyed once it exits the method, constructor, or block.
  • There is no default value for local variables, so local variables should be declared and an initial value should be assigned before the first use.
  • Local variables are implemented at stack level internally.
  • Access modifiers cannot be used for local variables.
  • Local variables are visible only within the declared method, constructor, or block.
Program to find Age in Java

Here in this example, age is a local variable. This is defined inside pupAge() method and its scope is limited to only this method.

public class Test {
   public void pupAge() {
      int age = 0;
      age = age + 7;
      System.out.println("Puppy age is : " + age);
   }

   public static void main(String args[]) {
      Test test = new Test();
      test.pupAge();
   }
}

Output

Puppy age is: 7
Error at the time of compilation in Java.

Following example uses age without initializing it, so it would give an error at the time of compilation.

public class Test {
   public void pupAge() {
      int age;
      age = age + 7;
      System.out.println("Puppy age is : " + age);
   }

   public static void main(String args[]) {
      Test test = new Test();
      test.pupAge();
   }
}

Output:

Test.java:4:variable number might not have been initialized
age = age + 7;
         ^
1 error

instance Java variable

  • A variable that is declared inside the class but outside the method is called instance variable.
  • It is not declared as static.
  • Instance variables have default values. For numbers, the default value is 0, for Booleans it is false, and for object references it is null. Values can be assigned during the declaration or within the constructor.
  • Instance variables can be accessed directly by calling the variable name inside the class. However, within static methods (when instance variables are given accessibility), they should be called using the fully qualified name. ObjectReference.VariableName.
  • Instance variables are created when an object is created with the use of the keyword ‘new’ and destroyed when the object is destroyed.
  • Instance variables hold values that must be referenced by more than one method, constructor or block, or essential parts of an object’s state that must be present throughout the class.
  • Instance variables can be declared at the class level before or after use.
  • Access modifiers can be given for instance variables.
  • The instance variables are visible for all methods, constructors, and block in the class. Normally, it is recommended to make these variables private (access level). However, visibility for subclasses can be given for these variables with the use of access modifiers.

Program to Print Name and Age in Java

public class Record{

    public String name;// this instance variable is visible for any child class.

    private int age;// this instance age variable is visible in Record class only.

    public Record (String RecName)
    {
        name = RecName;
    }

    public void setAge(int RecSal)
    {
        age = RecSal;
    }

    public void printRec()
    {
        System.out.println("name : " + name ); // print the value for “name”
        System.out.println("age :" + age); //prints the value for “age”
    }

    public static void main(String args[])
    {
        Record r = new Record("Ram");
        r.setAge(23);
        r.printRec();
    }
}

Output:

name : Ram
age :23

static Java variable

  • A variable that is declared as static is called static variable. It cannot be local.
  • The static variable is created when the program starts and destroyed when the program stops.
  • Visibility is similar to instance variables. However, most static variables are declared public since they must be available for users of the class.
  • Static variables can be accessed by calling the class name ClassName.VariableName.
  • There would only be one copy of each class variable per class, regardless of how many objects are created from it.
  • Default values are same as an instance variable. For numbers, the default value is 0; for Booleans, it is false; and for object references, it is null. Values can be assigned during the declaration or within the constructor. Additionally, values can be assigned in special static initializer blocks.
  • When declaring a class variable as public static final, then variable names (constants) are all in upper case. If the static variables are not public and final, the naming syntax is the same as instance and local variables.
Program to find Department Average Salary
import java.io.*;
public class Employee {

   // salary  variable is a private static variable
   private static double salary;

   // DEPARTMENT is a constant
   public static final String DEPARTMENT = "Development ";

   public static void main(String args[]) {
      salary = 2000;
      System.out.println(DEPARTMENT + "average salary:" + salary);
   }
}

Output:

Development average salary:2000

Ask your questions and clarify your/others doubts on for loop in Java Variable by commenting. Documentation.

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