In this article, we will discuss some of the key terms used in programming languages.
Often, we get confused with few terms in the programming world;
- Declaration
- Defining or definition
- Initialization
- Instantiation
- Instance of a class
Java Class
- First, let us try to understand what all a class contains in OOPS or in specific Java;
- A class consists of
- member variables (fields)
- behavior (methods or functions)
Student.java
package in.bench.resources.key.terms.in.java;
public class Student {
// member variables or fields
int studentRollNo;
String studentName;
int studentAge;
// instance method of a class
public void getStudentResult() {
// method definition goes here
}
}
Let us go through each terms in details with example & explanation;
1. Declaration:
- So when a member variables is declared without any value associated with it OR
- When method is just declared (method prototype with no body & ending with semi-colon(;))
- Then, it is simply referred as declaration
- Example: interface and abstract methods inside abstract class
- Note: all methods inside interface are abstract till Java 7 version
Example 1: with interface
Student1.java
package in.bench.resources.key.terms.in.java;
public interface Student1 {
// member variables or fields
// methods
public void getStudentDetails();
}
Example 2: with abstract class
Student2.java
package in.bench.resources.key.terms.in.java;
public abstract class Student2 {
// member variables or fields
int studentRollNo;
String studentName;
int studentAge;
// abstract method
public abstract void getStudentDetails();
}
2. Definition or Initialization:
- Now, when we declare any member variable & assign some values to variables, then member variable is said to defined or initialized
- Also, if a method is defined with body (with logic inside opening-closing curly braces), then it is said to be method definition (as against abstract method when we said just declaration)
- Examples: concrete classes
Student.java
package in.bench.resources.key.terms.in.java;
public class Student {
// member variables or fields
int studentRollNo = 1001;
String studentName = "Pup";
int studentAge = 35;
// instance method of a class
public void getStudentResult() {
// method definition goes here
}
}
3. Instantiation:
- When a blue-print or full-fledged class is defined with its member variables and method definition, then we need to create or instantiate an object; so as to access all possible variables and methods
- Instantiate is the very correct word used (instead of create, which is used to understand in laymen terms)
Student.java
package in.bench.resources.key.terms.in.java;
public class Student {
// member variables or fields
int studentRollNo = 1001;
String studentName = "Pup";
int studentAge = 35;
// instance method of a class
public void getStudentResult() {
// method definition goes here
System.out.println("Sample method "
+ "invocation for Student with details: \n");
System.out.println("Roll No.:- " + studentRollNo);
System.out.println("Name:- " + studentName);
System.out.println("Age:- " + studentAge);
}
// main() method
public static void main(String args[]) {
// instantiate or create an Object of type Student
Student student = new Student();
// invoking method using newly instantiated Student Object
student.getStudentResult();
}
}
Output:
Sample method invocation for Student with details:
Roll No.:- 1001
Name:- Pup
Age:- 35
4. Instance of a class:
- Whenever we instantiate or create an object of a class, then that particular reference variable is referred as instance of that class
- Generally, when we instantiate an object, there is always new operator associted with it for the creation of new object
- Using instanceOf operator, we can always check or verify whether particular reference variable is an instance of a class or NOT
Student.java
package in.bench.resources.key.terms.in.java;
public class Student {
// member variables or fields
int studentRollNo = 1001;
String studentName = "Pup";
int studentAge = 35;
// instance method of a class
public void getStudentResult() {
// method definition goes here
}
// main() method
public static void main(String args[]) {
// instantiate or create an Object of type Student
Student student = new Student();
// verifying using instanceof operator
if(student instanceof Student) {
System.out.println("It is an instance "
+ "of class Student !!");
}
else {
System.out.println("NOT an instance "
+ "of class Student !!");
}
}
}
Output:
It is an instance of class Student !!
Its time for you folks to reply back with your comments and sugestion
Happy Coding !!
Happy Learning !!