Abstract Classes and Methods in java
In the Java programming language, both abstract classes and abstract methods are fundamental concepts of object-oriented programming (OOP), inspired by C++ programming. Abstract classes and abstract methods in Java help Java programmers define a common structure data type layout format for other classes. This allows Java developers to apply a similar class structure layout to a class, providing easy implementation and flexibility.
So, let’s take a closer look at both abstract classes and abstract methods in Java.
Abstract Classes in Java.
An abstract class in Java programming is a user-defined class structure that cannot be automatically instantiated within an existing class. This means that the abstract class must first be converted to a subclass through another class. Which provides a strong class usage or implementation of the methods of a user-created abstract class.
Abstract Classes Features in Java.
- Cannot be instantiated – Remember, Java users cannot directly create an object of an abstract class in a program.
- Can have abstract methods – A user-declared abstract class can contain custom-defined methods that are declared in a class, but are not defined in the proper order as abstract methods, making the implementation dependent on subclasses.
- Can have concrete (non-abstract) methods – A user-defined abstract class can also contain multiple class methods implemented in a custom order, which can then be inherited by subclasses of the class if needed.
- Can have fields and constructors – Abstract classes in Java programs can have custom programmer-declared instance variables and constructor methods, just like normal user classes declare. Inheritance features in Java are a subclass concept that allows an abstract class to be extended further if needed. An abstract class must either implement all the abstract methods of the parent class in its properties or be defined with an abstract nature.
Java abstract class syntax.
abstract class Course {
// Here we declare an abstract class method with no body portion
public abstract void select_course();
// Here we Concrete a class method
public void select() {
System.out.println(“You can select a course.”);
}
}
In the abstract class example here.
- Here, select_course() in the abstract class is an abstractly defined class method, which means that its implementation is not provided in the Course class. The Java user must provide the implementation in a subclass.
- Here, select() in the abstract class is a user-created concrete method, with a complete implementation provided in the Course class.
Example of an abstract class in Java.
abstract class Course {
// Here we define an abstract method with no body
public abstract void select_course();
// Here we create a concrete class method
public void select() {
System.out.println(“You can select your desire programming.”);
}
}
class Java extends Course {
// Here we provide the implementation for the abstract class method
@Override
public void select_course() {
System.out.println(“Java select”);
}
}
class Python extends Course {
// here we Provide the implementation for the abstract method
@Override
public void select_course() {
System.out.println(“Python selected”);
}
}
public class Main {
public static void main(String[] args) {
//here it Cannot instantiate the abstract class Course
//here Course course = new Course(); // display error
Course java = new Java();
java.select_course(); //Java select
java.select(); //This course is selected.
Course python = new Python();
python.select_course(); //Python select
python.select(); //This course is selected“.
}
}
Explaining abstract class Java.
- In this program, Course is an abstract class, declaring a super or main class in which an abstract method (select_course()) and a concrete method (select()) are created and defined.
- These Java and Python classes extend the Course class and provide their implementations through the select_course() method.
- The Main class here represents where Java users cannot directly instantiate the abstract class automatically. As such, Java users can create new objects for a subclass. Java and Python subclasses provide implementations for the abstract class methods.
Java Abstract Class Methods.
In a Java class program, an abstract method is a user-defined class method that is defined in an abstract class or interface, but no implementation is provided in that class. The implementation of the abstract class method is left to the subclass.
Features of Java Abstract Class Methods.
- No implementation – An abstract class method declared in a Java class defines only a method signature, without a body. No code is created within the declared class method.
- Subclass must have implementation – Any concrete non-abstract subclass defined in a subclass must provide an implementation for all abstract methods of the parent class, unless the subclass also has a proper abstract implementation.
- Cannot have a body − Remember, a user defined abstract class method cannot have any code defined in it.
Java abstract class method syntax.
abstract class Course {
// here we define an Abstract class method with no body element
public abstract void select();
}
Explain with Abstract Method:
abstract class Course {
// here we define an Abstract class method with no body element
public abstract void select();
}
class Java extends Course {
// here we Provide the implementation for the abstract class method
@Override
public void select() {
System.out.println(“Java selected”);
}
}
public class Main {
public static void main(String[] args) {
//here it Cannot instantiate the abstract class Course
// Course course = new Course(); //it displays error
Course java = new Java();
java.select(); // Java select
}
}
Here in the Abstract Class Methods example.
- The select() method in the Course class is an abstract class method, which means it must be implemented or properly defined in any subclasses before use.
- Similarly, Java provides an implementation for subclass select().
