Abstract class, interface, abstract class Interface
Why use abstract classes:
If the subclass is not correctly rewritten, no prompt is displayed.
Assume that the code of the parent class is as follows:
public class USB { public void QiDong(){ } public void TingZhi(){ }}
The code in the subclass is as follows: rewrite the method in the parent class
Public class UPan extends USB {public void Qidong () {// Qidong here is not a rewriting of the parent class function System. out. println ("U disk started");} public void TingZhi () {System. out. println ("the USB flash disk stops running ");}}
Such code will not report errors in Eclipse;
Abstract class: a class that does not know what it is.
Description: abstract class name
public abstract class USB {}
Abstract method: I don't know what the specific method is;
Writing Method: abstract return type function name (parameter); abstract method does not need to write function body
In a derived class, certain abstract methods are not implemented, but the derived class must be declared as an abstract class.
Abstract classes can have abstract methods or non-abstract methods. Abstract classes can also contain member variables.
public abstract class USB { public String JiaGe; public abstract void QiDong();
public abstract void TingZhi(); }
Interface:
The role of the interface: It mainly serves as a constraint. It can be understood that the code format of a large frame can only be written in the specified format.
Definition: file-New-interface // The first letter of the interface name plus an uppercase I
When defining an interface, the interface name should be an adjective or descriptive word.
Interface content as few as possible for convenient and flexible use-interface separation principle
Interface Name extends parent interface list {final type constant name = value; // specifies the format in which to write data. If the format is different from the format, public void method name (parameter) will be reported );}
Interface implementation:
Abstract class name extends parent class implements interface list {
}
As mentioned above, the interface serves as a constraint, so let's take a look at how it is constrained.
Create an interface-enter the following code in the interface
public interface IJiSuan { public int a=0; public void Suan(int a, int b);}
Then we create a new class-class add interface, click OK, the following code is automatically generated;
Public abstract class YunSuan implements IJiSuan {@ Override public void Suan (int a, int B) {// method stub automatically generated by TODO }}
If we change the method name to suan, an error is automatically reported.
Final can modify member variables (constants), member methods (not allowed to be rewritten), classes (not allowed to be inherited)