In Java, variables are storage containers which store any type of input values . Understanding java variable is important to learn java programming.
Main Components of Variables in Java:
A variable in java has 3 components:
- Data Type:Defines the kind of data stored (e.g., int,double,float,String)
- Variable Name: A unique identifier following the java naming rules.
- Value: The actual data assigned to the variable.
2 RULES TO USE VARIABLES IN JAVA APPLICATION:
(1) Variable Declaration
(2) Variable Initialization
How to declare a variable in Java?
To declare a variable in java , we need to take care of two things which are:
1.Data type: In java,data type define the type of data which a variable can hold.
2.Variable Name: Variable Name must follow the java naming convention.
eg: int sum;
double salary;
where int, double are data type & sum,salary are variable name.
How to initialize Java Variables?
We can initialize Java Variables as given below:
int sum=88;
Where int is the data type , sum is the variable name and 88 is the value assigned.
Types of Java Variables:
Different types of Java variables are as listed below:
(1)Local Variables
(2) Instance Variables
(3) Static Variables
(1) Local Variables: A variable defined within a block or method or constructor is called a local variable.
- Local variables are created at the time of declaration and destroyed when the method or function completed it’s execution.
- Local variable need to be initialized first before using it within it’s scope.
- The scope of the local variables exists only within the method or block in which they are declared
Example: This example shows how a local variable is declared and used within the main method.
class A{
public static void main(String args[]){
//Declared a local variable
int num=88;
//this variable num is local to the main method only
System.out.println(“Local variable:”+num);
}
}
Example: This example shows how a local variable is declared and used inside a normal method and it can’t be used outside of it.
class B{
public static void main(String args[]){
static int a=10;
void display(){
//Declaring a local variable
int b=88;
//this variable b is local to the method display() only
System.out.println(“Local variable:”+b);
}
}
}
In the above example variable b is local to the method display() only & it can’t be access outside of this display() method.
(2) Instance Variable: Instance variables are known as non-static variables which are declared in a class outside of any method,constructor or block.
- Instance variable of a class is created when an object of the class is created and destroyed when the object of the class is destroyed.
- Initialization of instance variable is not mandatory. It’s default value depend on the data type of the variable. For int, it is 0, for String it is null , for float it is 0.0f etc.
- We may use access specifiers for instance variables. If we don’t specify any access specifier, then default access specifier will be used.
- Scope of the instance variable are throughout the class except the static contexts. For eg: If we use instance variable inside the static main method it will give error. If we want to access the instance variable inside the static method, first we have to create the object of the class , then with the help of object reference one can access that instance variable inside static main method.
- Instance variables can be accessed by creating objects.
- Instance variables can be initialized using constructors while creating an object. One can also used instance blocks to initialize the instance variables.
Example: This example shows the use of instance variables in a class.
import java.io.*;
class A{
//Declared instance variable
public String name;
public int i;
public A(){
//Default constructor
//initializing instance variable
this.name=”Joy”;
}
//Declaring main method
public static void main(String args[]){
//Object creation
A a=new A();
//Displaying output
System.out.println(“name is:”+a.name);
System.out.println(“Default value for int is:”+a.i);
}
}
Output
name is : Joy
Default value for int is: 0
(3) Static Variables: Static variables are variables which are declared with static keyword and also known as class variables.
- Static variables are created at the start of program execution and destroyed automatically when execution ends.
- One class can have only one copy of static variable , irrespective of how many objects we create.
- Initialization of static variable is not mandatory. If we don’t initialize the static variable it will print the default value. For String default value is null , for int it is 0 , for float it is 0.0 etc.
- One can access the static variables with the help of class name without creating the object of a class which saves the memory of the class.
- Static blocks can be used to initialize the static variable.
Example: This example describes the use of static variable, which belong to the class and can be accessed without creating an object of the class.
//Java program of static variables
import java.io.*;
class A{
//Declaration of static variable
public static String name=”Joy”;
public static void main(String args[]){
//Displaying the name without creating the object of class with the help of class name
System.out.println(“name is:”+A.name);
}
}
Output: name is: Joy
Instance Variable vs Static Variables
- Static variables belong to class itself. Whereas, Instance variables belongs to a specific object of the class.
2. Static variable allocated memory once, at the time of class is loaded.
Whereas instance variables allocated memory for each object of the class
3. Static variables are initialized only once when the class is loaded.
Whereas, instance variable initialized each time a new object is created
4.Static variables can be easily accessed within a static context
Whereas,instance variable can’t be accessed within a static context directly without creating the object reference.
5. Static variables can be easily accessed within a instance context or instance method.
But instance variable can be accessed within instance context only , not within static context.
Q1. What is variable in java?
Answer: Variable in java is a storage container to store any type of supported input value by java.