Flash cards
Review the key moves
What is the main idea behind Java Abstraction?
Lesson checks
Practice each idea before moving on
Short Mimo-style checks built from this lesson's code, terms, and sequence.
Which statement best captures the main point of this lesson?
Complete the missing token from the example code.
abstract ___ Animal {Put the learning moves in the order that makes the concept easiest to apply.
Abstract Classes and Methods
Data abstraction is the process of hiding certain details and showing only essential information to the user. Abstraction can be achieved with either abstract classes or interfaces (which you will learn more about in the next chapter).
- Abstract class: is a restricted class that cannot be used to create objects (to access it, it must be inherited from another class).
- Abstract method: can only be used in an abstract class, and it does not have a body. The body is provided by the subclass (inherited from).
An abstract class can have both abstract and regular methods:
abstract class Animal {
public abstract void animalSound();
public void sleep() {
System.out.println("Zzz");
}
}From the example above, it is not possible to create an object of the Animal class:
Animal myObj = new Animal(); // will generate an errorTo access the abstract class, it must be inherited from another class. Let's convert the Animal class we used in the Polymorphism chapter to an abstract class:
Remember from the Inheritance chapter that we use the extends keyword to inherit from a class.
Example
// Abstract class abstract class Animal { // Abstract method (does not have a body) public abstract void animalSound(); // Regular method public void sleep() { System.out.println("Zzz");
}
}
// Subclass (inherit from Animal) class Pig extends Animal { public void animalSound() { // The body of animalSound() is provided here System.out.println("The pig says: wee wee");
}
}
class Main {
public static void main(String[] args) {
Pig myPig = new Pig(); // Create a Pig object
myPig.animalSound();
myPig.sleep();
}
}To achieve security - hide certain details and only show the important details of an object.
Note
Abstraction can also be achieved with Interfaces , which you will learn more about in the next chapter.