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This article introduces the knowledge of "what are the characteristics of Java object-oriented". In the operation of practical cases, many people will encounter such a dilemma, so let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

Java is an object-oriented language. The main features of object-oriented are encapsulation, inheritance and polymorphism.

Encapsulation means encapsulating ("hiding") some attributes of the class, avoiding direct access to some attributes of the object as far as possible, in order to ensure its security, if we have to access these attributes, we can separately provide some interfaces (common methods) for access, so that we can avoid misoperation caused by direct access to attribute information.

Inheritance, there are also a lot of inheritance relationships in our lives, for example, children inherit from their parents. In Java, we can also have the concept of inheritance, but inheritance only exists in parent-child classes (interfaces). For example, we often say that Dog class inherits from Animal class, animal class Animal has some properties of its own, Dog belongs to a kind of Animal, so it has some properties of Animal, but Dog also has some specific attributes of its own. At this time, if we are alone in recreating a class Dog, we need to rewrite the properties of the Animal class, which is time-consuming and difficult to maintain, then we can use inheritance and use the Dog class to inherit the Animal class. At this time, Dog contains some properties of the Animal class, and we do not need to rewrite these attributes many times.

Polymorphism, that is, different results may be executed for the same object. For example, in the Animal class above, we create two subclasses of Dog and Cat,Animal. There is a method called public void jiaoSheng () {System.out.println ("animal barking");} two subclasses rewrite this method to implement the form Dog:public void jiaoSheng () {System.out.pringln ("dog barking"). }, Cat: public void jiaoSheng () {System.out.println ("cat barking");}, at this point we can create an Animal object animal = new Animal (); at this point we call animal.jiaoSheng (); print out "animal barking"; when animal = new Dog (); we call animal.jiaoSheng (); print out "dog barking"; when animal = barking () When we call animal.jiaoSheng (); print out "cat bark"; for the same object animal, when we call the same method, the printed results are different. Using polymorphism, we can make a lot of extensions without having to modify the original code too much to ensure the maintainability of the code. We can see from the above that if we want to have polymorphism, we need to meet three conditions, the first is to inherit (or implement the interface), and the second is to rewrite the methods in the parent class, otherwise we will not implement polymorphism. The object still calls the method of the parent class, and the third parent class reference points to the subclass object, just like the above animal, which is an object of the Animal class, but when we new Two objects of the subclasses Dog and Cat are created

Here is an example of the source code:

Public class Animal {

Public void jiaoSheng () {

System.out.println ("animal calls")

}

}

Public class Dog extends Animal {

@ Override

Public void jiaoSheng () {

System.out.println ("dog barking")

}

}

Public class Cat extends Animal {

@ Override

Public void jiaoSheng () {

System.out.println ("cat barking")

}

}

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