Java Learning Notes---Inheritance and the use of super

Since the change of a video teaching, feel better than the original, is the school speed is too slag, a lot of video to see a card half a day, can only look at the downloaded already.

However, although it can not start from the beginning to reopen, but have seen once, in a look is also good, when the consolidation study.

Inherited keyword: extends

The format is as follows: Class subclass name extends parent class name {

...

}

Students, for example, inherit the father of the human species.

Class Student extends person{

...

}

If the declaration of a class does not use the keyword extends, the class inherits the object class by default. Object is the parent class of all classes. Object is a class in the Java.lang package.

When a subclass inherits a parent class, the child class can invoke all methods and member variables in the parent class. Subclasses can also declare methods or variables themselves individually.

The following code creates 4 classes. is Dog,cat,animal and main class containing the main function respectively. where dog and Cat inherit the parent class animal.

Cat inherits the Animal class:

Package com.cnblogs;

public class Cat extends animal{

Default constructor with no parameters

Public Cat () {

Super (); must appear in the first row of the construction method. This ();

Super ();

Super ("XX", 10); The code represents the constructor that invokes the parent class with a parameter

System.out.println ("Cat Builder"); }

/ * public String name;

public int age;

public void Walk () {

System.out.println ("Cat....walk");

}

public void sleep () {

System.out.println ("Cat....sleep");

}  */

Note hints

@Override

public void How () {

SYSTEM.OUT.PRINTLN (name + "" + "Cat....miaomiao");

Super enforces the call Show () method method of the parent class.

If there is no super,show (); is this.show (); The default notation.

The steps are: the show () method of the subclass is called first. Subclasses call the show () method of the parent class without the Show method

Super.show ();

}

public void Show () {

SYSTEM.OUT.PRINTLN (name + "" + "Cat----->show");

}

}

Declare the Dog class:

Package com.cnblogs;

public class Dog extends Animal {

/*public String name;

public int age;

public void Walk () {

System.out.println ("Dog....walk");

}

public void sleep () {

System.out.println ("Dog....sleep");

}  */

public void How () {

SYSTEM.OUT.PRINTLN (name + "" + "Dog....wangwang"); }

}

To create a animal parent class:

Package com.cnblogs;

Animal does not write inheritance is the default Inheritance object class. Abstract classes cannot be new. An instance object that is passed in as a subclass.

Public abstract class Animal extends object{

public String name;

public int age;

Default constructor with no parameters

Public Animal () {

This ("Baobao", 2);

This () is called the method of animal with the following parameter

System.out.println ("Animal---> ()");

}

constructor with parameter. Assigning an initial value to a property

Public Animal (String Name,int age) {

THIS.name = name;

This.age = age;

System.out.println ("Animal---> (name,age)");

}

public void Walk () {

SYSTEM.OUT.PRINTLN (name + "---->walk");

Sleep ();

how ();

This.show calls the show () method of the subclass, if the subclass does not have the show () method. Call the show () method of the parent class.

This.show ();

}

public void sleep () {

SYSTEM.OUT.PRINTLN (name + "---->sleep");

}

Abstract method.

public abstract void how ();

public void Eat () {

SYSTEM.OUT.PRINTLN (name + "---->eat");

}

public void Play () {

SYSTEM.OUT.PRINTLN (name + "---->play");

}

public void Show () {

SYSTEM.OUT.PRINTLN (name + "" + "Animal---->show");

}

}

Main Class (contains main function):

Package com.cnblogs;

public class Main {

public static void Main2 (string[] args) {

Build a Cat Object

Cat cat = new Cat ();

Cat.name = "Xiaohua";

Cat.age = 3;

Cat.walk ();

Cat.how ();

Generate a Dog object

Dog dog = new Dog ();

Dog.name = "Xiaomei";

Dog.age= 3;

Dog.walk ();

Dog.eat ();

Dog.how ();

Call the object that is being tuned out

Animal Animal = new Cat ();

Animal.name = "HH";

called the How () method of the subclass Cat ().

Animal.how ();

Animal animal2 = new Dog ();

Animal2.name = "XX";

How to call the Subclass dog ()

Animal2.how ();

Animal.walk ();

The Getmsg method requires that the subclass cat be passed in, so it must be cat, not animal.

Getmsg (CAT);

Getmsg (dog);

Getmsg (ANIMAL2);

}

/* public static void getmsg (Cat cat) {

Cat.how ();

}*/

The reference to the subclass's object passed to the parent class//is more flexible than the incoming individual cat above, typically using the following method

public static void Getmsg (Animal Animal) {

Animal.how ();

}

/** * * *. The new object first calls the first method of the subclass cat, runs Super (), and invokes the first method of the parent class animal

* *. The constructor method in the parent class executes this () method, and the This method calls the method with the animal parameter and outputs it; executes this () on the constructor that returns no parameters; The following output statement

. Execute super () in the return subclass cat; The following statement, output "Cat builder"

. Then Animal.how () calls the new Object cat's How () method

. Executes the How () method in the subclass Cat () method, and outputs.

*6.    Next, you run Super (). Show in the How () method, and then call the show () method of the parent class animal. and output the corresponding result. * */

public static void Main (String [] args) {

Animal Animal = new Cat ();

Animal.how (); }

}

Super (); call the constructor, methods, and properties of the parent class.

This (); invokes the current object of the method.

Today, the blog park can not be inserted code block, do not know what problems can only be handwritten, write a half-day. Look at the head is dizzy.

Java Learning Notes---Inheritance and the use of super