Variables are the basic units used to store any information in Java. The variable name is the name allotted for these units. A Java code may need information in the form of a numeric or a string value. The same set of values may be required in multiple stages of a code. This is where a variable comes into the picture.
All these required values can be assigned to different variables that will be stored in their respective memory locations; hence a variable is nothing but the name of a memory location. Storing values to variables is more efficient than repeating the values everywhere in the code. Also, it helps when there is a change in the value required, as just changing it at one place of the variable declaration will be sufficient rather than having to change at multiple locations.
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A variable cannot be used until and unless it is declared, and the datatype we assign during declaration defines the type of value it can hold. Various data types such as int, float, string, char, Boolean, long, double can be assigned to a variable.
The general syntax to declare a variable in Java is as follows:
Ex: int a = 1;
Where,
The following diagram gives the pictorial representation of the same:
Assigning a default value to the variable is called the initialization of that variable. A variable can be initialized both during declaration and during the later stages of the program as required. Examples: Following are some of the values we can assign to a variable with respect to its particular data type:
There are 3 types of variables in Java:
Example: In the following example, we are considering “num” and “name” as local variables. Code:
public class PatientDetails{
public void Patient()
{
// local variable num
//local variable name
int num = 1200;
string name = "Harish";
id = id + 1;
System.out.println("Patient Name is: " + name + " Patient Number is: " + num);
name = "Sudha";
System.out.println("Patient Name is: " + name + " Patient Number is: " + num);
}
public void DoctorDetails()
{
int num = 12000;
string name = "Vijay";
num = num +1;
System.out.println("Doctor Name is: " + name + " Doctor ID is: " + num);
name = "Suma";
System.out.println("Doctor Name is: " + name + " Doctor ID is: " + num);
}
public static void main(String args[])
{
PatientDetails pat = new PatientDetails();
pat. Patient();
pat.DoctorDetails();
}
}Output:
The patient Name is: Harish
Patient Number is: 1200
The patient Name is: Sudha
Patient Number is: 1201
Doctor Name is: Vijay
Doctor ID is: 12000
Doctor Name is: Suma
Doctor ID is: 12001
This shows that the same local variable names “num” and “name” when declared in two different methods, i.e. Patient and DoctorDetails, can be used for assigning any number of different values.
Example:
The same local variables “num” and “name” will be invalid if we try to display their value outside of their method.
Code:
public class PatientDetails{
public void Patient()
{
// local variable num
//local variable name
int id = 1200;
}
public static void main(String args[])
{
System.out.println("Patient Number is: " + num);
//printing local variable outside it's method
}
}Output:
Compilation Error in java code:-
prog.java:12: error: cannot find symbol
System.out.println(“Patient Number is: ” + num);
^
symbol: variable num
location: class PatientDetails
1 error
Example:
Here a, b, c are the instance variables that are declared in two different instances by two different objects.
Code:
import java.io.*;
class Marks {
// a, b, c are instance variables
// a, b, c variables are being declared inside a class and not function
int a;
int b;
int c;
}
class MarksDemo {
public static void main(String args[])
{
// first object declaration
Alpha alp1 = new Alpha();
alp1 .a= 44;
alp1 .b= 77;
alp1 .c= 88;
// second object declaration
Alpha alp2 = new Alpha();
alp2 .a= 77;
alp2 .b= 55;
alp2 .c= 74;
// displaying variable values for first object
System.out.println("Values for first object:");
System.out.println(alp1.a);
System.out.println(alp1.b);
System.out.println(alp1.c);
// displaying variable values for second object
System.out.println("Values for second object:");
System.out.println(alp2.a);
System.out.println(alp2.b);
System.out.println(alp2.c);
}
}Output:
Values for the first object:
44
77
88
Values for the second object:
77
55
74
Example:
Code:
import java.io.*;
class Students {
//static variable rollno
public static double rollno;
public static String name = "Lilly";
public static classnum;
}
public class StudentDetails {
public static void main(String args[])
}
{
// no need of object to access static variables
Students .rollno= 101;
Students.classnum=3;
System.out.println(Students .name + "'s rollno is:" + Students .rollno + "and class number is:" + Students.classnum);
}
}Output:
Lilly’s rollno is 101, and the class number is: 3
Variables form the elemental part of a Java program. They point to a particular memory location when they are created, and the same is released when the object is not referenced anymore. This memory which is released, will be swept away when garbage collection takes place. This process can also be considered as the life cycle of a variable.
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