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Java Variable Types



Following examples of variable declaration and initialization in Java −
Example
int x, y, z;         // Declares three ints, x, y, and z.
int x = 10, y = 25;  // Example of initialization
byte Y = 24;         // initializes a byte type variable Y.
double pi = 3.14159; // declares and assigns a value of PI.
char x = 'x';        // the char variable a iis initialized with value 'x'

Three type of variable
  • Local variables
  • Instance variables
  • Class/Static variables


Local Variables

  • Access modifiers cannot be used for local variables.
  • Local variables are declared in methods, constructors, or blocks.
  • Local variables are visible only within the declared method, constructor, or block.

Example
public class Test {
   public void pupAge() {
      int age = 0;
      age = age + 9;
      System.out.println("Puss age is : " + age);
   }

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

Run example »
output
Puss age is: 9
Following example uses age without initializing it, so it would give an error at the time of compilation.

Example

public class Test {
   public void pupAge() {
      int age;
      age = age + 9;
      System.out.println("Puss age is : " + age);
   }

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

Output
/Test.java:4: error: variable age might not have been initialized
      age = age + 9;
            ^
1 error

Instance Variables

  • Access modifiers can be given for instance variables.
  • Instance variables can be accessed directly by calling the variable name inside the class.
  • Values can be assigned during the declaration or within the constructor.


import java.io.*;
public class Student {

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

    // salary  variable is visible in Student class only.
    private double salary;

    // The name variable is assigned in the constructor.
    public Student (String empName) {
        name = empName;
    }

    // The salary variable is assigned a value.
    public void setSalary(double empSal) {
        salary = empSal;
    }

    // This method prints the Student details.
    public void printEmp() {
        System.out.println("name  : " + name );
        System.out.println("salary :" + salary);
    }

    public static void main(String args[]) {
        Student empOne = new Student("Nicki Minaj");
        empOne.setSalary(50000);
        empOne.printEmp();
    }
}

Run example »
output
name  : Nicki Minaj
salary :50000.0


Class/Static Variables

  • Static variables are stored in the static memory
  • tatic variables are created when the program starts and destroyed when the program stops.
  • Static variables can be accessed by calling with the class name ClassName.VariableName.
import java.io.*;
public class Employee {

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

    // developer is a constant
    public static final String developer = "job ";

    public static void main(String args[]) {
        salary = 83000;
        System.out.println(developer + "average salary:" + salary);
    }
}

Run example »
output job average salary:83000.0