Java Variable Types – The Geek Diary

Following are 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();
   }
}

output

Puss age is: 9

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 + 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();
    }
}

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);
    }
}

output

job average salary:83000.0

Local Variables

Instance Variables

Class/Static Variables

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