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Java Variable Types

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In Java, all variables must be declared before they can be used. The basic form of a variable declaration is shown here:

type identifier [ = value][, identifier [= value] ...] ;

The type is one of Java's datatypes. The identifier is the name of the variable. To declare more than one variable of the specified type, use a comma-separated list.

Here are several examples of variable declarations of various types. Note that some include an initialization.

int a, b, c;         // declares three ints, a, b, and c.
int d = 3, e, f = 5; // declares three more ints, initializing
                     // d and f.
byte z = 22;         // initializes z.
double pi = 3.14159; // declares an approximation of pi.
char x = 'x';        // the variable x has the value 'x'.

This chapter will explain various variable types available in Java Language. There are three kinds of variables in Java:

  1. Local variables

  2. Instance variables

  3. Class/static variables

Local variables :

Example:

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

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();
   }
}

This would produce following result:

Puppy age is: 7

Example:

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();
   }
}

This would produce following error while compiling it:

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

Instance variables :

Example:

import java.io.*;

class Employee{
   // this instance variable is visible for any child class.
   public String name;
   
   // salary  variable is visible in Employee class only.
   private double salary;
   
   // The name variable is assigned in the constructor. 
   public Employee (String empName){
      name = empName;
   }

   // The salary variable is assigned a value.
   public void setSalary(double empSal){
      salary = empSal;
   }
   
   // This method prints the employee details.
   public void printEmp(){
      System.out.println("name  : " + name );
      System.out.println("salary :" + salary);
   }

   public static void main(String args[]){
      Employee empOne = new Employee("Ransika");
      empOne.setSalary(1000);
      empOne.printEmp();
   }
}

This would produce following result:

name  : Ransika
salary :1000.0

Class/static variables :

Example:

import java.io.*;

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 = 1000;
      System.out.println(DEPARTMENT+"average salary:"+salary);
   }
}

This would produce following result:

Development average salary:1000

Note: If the variables are access from an outside class the constant should be accessed as Employee.DEPARTMENT

What is Next ?

You already have used access modifiers ( public & private ) in this chapter. The next chapter will explain you Access Modifiers and Non Access Modifiers in detail.


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