Java_ Abstract class

Abstract class
1, syntax definition
Abstract keyword is used to decorate the class before it is abstract class
2. Application Scenarios
(1) In some cases, a parent class simply knows how its subclasses should be, but does not know exactly how these subclasses implement these methods.

(2) abstract an abstract class from multiple classes with the same characteristics, using this abstract class as a template for subclasses, thus avoiding the arbitrariness of sub-class design

3. Role

Restriction subclasses must implement some methods, but do not care about implementation details

(Main purpose: Do not focus on the implementation of subclasses.) But what subclasses must be constrained to constrain subclasses)

4. Applicable methods (usage rules)

(1) abstract definition Abstraction class

(2) Abstract definition abstraction method, declaration only, do not need to implement

(3) classes that contain abstract methods are abstract classes

(4) An abstract class can contain ordinary methods, or there can be no abstract method

(5) Abstract classes cannot be created directly, you can define reference variables

* * Abstract class does not have a method body, but ends with a semicolon

Little Tricks

"syso+alt+/" System.out.println (""); shortcut keys

When creating a subclass, tick browse to select the parent class name

When creating a subclass, tick abstract to generate abstract classes directly

When creating a test class (Initail class Main method), tick the public static void main (string[] args) to generate directly:

public static void Main (string[] args) {

TODO auto-generated Method Stub

}

 public  abstract  class   Telphone { public  abstract     void   call ();  public  abstract  void   message ();}   

 public  class  CellPhone extends   Telphone {@Override  public  void   call () {System.out.println (" Phone by keypad "); @Override  public  void   message () { //  TODO auto-    Generated method stub  System.out.println ("Call through the keyboard" 

 class  SmartPhone extends   Telphone {@Override public  void   call () { //  T    ODO auto-generated Method Stub  System.out.println ("Can call by voice"  public  void   message () { //  TODO auto-    Generated method stub  System.out.println ("can be sent by voice message" 

 public  class   Initail { public  static  void   main (string[] args) { //  TODO auto-generated method stub  telphone tel1=new   CellPhone ();        Tel1.call ();        Tel1.message ();        Telphone tel2  =new   SmartPhone ();        Tel2.call ();    Tel2.message (); }}

Questions:
@Override  for the automatically generated code, what does that mean, what does it do?
For automatically generated code, what does that mean, what does it do?

Practice:

Existing shape Graphics class, he has two graphic classes, with rectangle rectangle and Circle Circle sub-class, to find the circumference and area of the circle.

Java_ Abstract class