0910 some basic concepts of Java abstract classes __java

Some basic concepts of abstract classes Directory

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Some basic concepts of abstract class catalog abstract conceptual code block

The concept of abstraction

Abstract method: In Java, a method without a method body is defined as an abstract method.
Abstract class: If there is an abstract method in a class, the class is defined as an abstract class.
1> Abstract class overview:
    animals should not be defined as specific things, and animals eat, sleep, etc. should not be specific.
    we call a function that is not specific as abstract, and if there is an abstract function in a class, the class must be an abstract class.  
2> The characteristics of abstract classes:
    A: Abstract classes and abstract methods must be decorated with the abstract keyword
    B: there is not necessarily an abstract method in an abstract class, but a class with an abstract method must be defined as an abstract class
    C: An abstract class cannot be instantiated
        because it is not concrete.
        Abstract classes have construction methods, but cannot be instantiated? What
        is the role of the construction method? Initialization of a subclass that accesses the parent class
    D: Abstract Subclass
        A: If you do not want to override an abstract method, the subclass is an abstract class.
        B: Rewrite all the abstract methods, this time the subclass is a concrete class. The instantiation of an

    abstract class is actually implemented by a specific subclass. is the polymorphic way.
        Animal a = new Cat ();
3> the members of an abstract class:
    member variables: can be either a variable or a constant.
    Construction Method: there is.
        used to initialize the subclass to access the data of the parent class.
    member methods: can be abstract or non-abstract.

4> The member method attributes of an abstract class:
    A: Abstract methods < forcing the subclass to do things >.
    B: Non-abstract methods < subclass inherited things, improve code reuse >

code block

code block syntax follows standard markdown code, such as:

abstract class animal{int age=20;
    final int age2=40;
    Public Animal () {} public Animal (String Name,int age) {} public abstract void Show ();
    public void Method () {System.out.println (' Animal method ');
    Class Dog extends animal{public void Show () {System.out.println (""); } public class AbstactDemo2 {public static void main (string[] args) {//TODO automatically generated method stub Animal A=ne
        W Dog ();
a.age=10;
        a.age3=30;
        System.out.println (A.age);
    System.out.println (A.age2); }
}