JAVA-Variable Types

Introduction to Java variables

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Java variables provide us with named storage and that can manipulate our programs. Each variable has a specific type as well and it determines the size and layout of the variable’s memory. A set of operations can be applied to the variable and the range of values will be stored in the variable’s memory.

There are three types of variables available in Java.

• Local variables
• Instance variables
• Class/Static Variables

Local Variables

• These variables are declared in methods, blocks or constructors.
• Created when the constructor, method or block is entered.
• Access modifiers cannot be used for this kind of variables and these are implemented at the stack level internally.
• Local variables should be declared and an initial value should be assigned before the first use since there is no default value for these variables.

Example:

public class Test1{ 
public void myAge(){ 
int age = 0;
age= age+7;
System.out.pritnln("My age is :" + age);

}
public static void main (String args[]){
Test1 test1 = new Test1();
test1.myAge();
}
}
//My age is: 7

Instance Variables

• These variables are declared in a class, but outside a constructor, method or any block.
• When the object is created these variables are created. When we creating an object we use the “new” keyword. Once this new keyword destroyed the object is also destroyed.
• These variables declared in a class level before or after use.
• These are having default values. As an example for numbers default value is 0, for boolean it's false.
• Can be accessed directly using the variable name which is used inside the class.

Example:

import java.io.*;
public class Student{  
// this instance variable is visible for any child class.  
public String name;   
// name variable is visible in Student class only. 
private double Marks; 
  // The name variable is assigned in the constructor.
public Student(String stuName){ 
 name = stuName; 
 }  
// The marks variable is assigned a value.
public void setMarks(double stuMarks)
{  marks= stuMarks;
  }   
// This method prints the employee details.  
  public void printStu(){
    System.out.println("name : " + name ); 
    System.out.println("marks :" + marks); 
}
public static void main(String args[]){ 
    Student stuOne = new Student("Maleesha"); 
    stuOne.setMarks(1000);  
    stuOne.printStu(); 
 
  } 
}

Class/Static Variables

• These variables declared with the “static” keyword in a class, but outside a method, block or constructor.
• These variables are declared as constants. Constant variables never change their initial values.
• Stored in static memory and rarely use these variables other than declared final and used as either public/private constants,
• These variables created when the program starts to running and destroys when it stopped.
• Can be accessed by calling with the class name ClassName.VariableName.

Example:

import java.io.*;
public class Emp{ 
// salary variable is a private static variable 
 private static double salary; 
// DEPARTMENT is a constant  
public static final String DEPARTMENT = "Fashion Design";  

public static void main(String args[]){  
salary = 120000;  
System.out.println(DEPARTMENT + "average salary:" + salary);
  }
}

//Fashion Design average salary:120000