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Improve comments on abstract classes

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Andrew Gallasch 2017-10-28 16:09:07 +10:30 committed by GitHub
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@ -703,15 +703,21 @@ public class ExampleClass extends ExampleClassParent implements InterfaceOne,
// // Method declarations
// }
// Marking a class as abstract means that it contains at least one abstract
// method that must be defined in a child class. Similar to interfaces, abstract
// classes cannot be instantiated, but instead must be extended and the abstract
// methods defined. Different from interfaces, abstract classes can contain a
// mixture of concrete and abstract methods. Methods in an interface cannot
// have a body, unless the method is static, and variables are final by default,
// unlike an abstract class. Also abstract classes CAN have the "main" method.
// Abstract Classes cannot be instantiated.
// Abstract classes may define abstract methods.
// Abstract methods have no body and are marked abstract
// Non-abstract child classes must @Override all abstract methods
// from their super-classes.
// Abstract classes can be useful when combining repetitive logic
// with customised behavior, but as Abstract classes require
// inheritance, they violate "Composition over inheritance"
// so consider other approaches using composition.
// https://en.wikipedia.org/wiki/Composition_over_inheritance
public abstract class Animal
{
private int age;
public abstract void makeSound();
// Method can have a body
@ -722,17 +728,12 @@ public abstract class Animal
age = 30;
}
// No need to initialize, however in an interface
// a variable is implicitly final and hence has
// to be initialized.
private int age;
public void printAge()
{
System.out.println(age);
}
// Abstract classes can have main function.
// Abstract classes can have main method.
public static void main(String[] args)
{
System.out.println("I am abstract");