1. Problems with formal parameters and return values
(1) Formal parameters:
A: Class Name: Objects that require this class
B: Abstract class Name: Sub-class object that needs to be changed
C: Interface Name: An implementation object that requires this interface
(2) Return value type:
A: Class Name: Abstract class Name: Returns the object of the class
B: Abstract class Name: Returns the subclass object of the class
C: Interface Name: Returns the Implementation class object for the interface
(3) Chain-type programming
Each time the method is called, an object is returned
2. Package
(1) is actually a folder
(2) Function:
A: Distinguish between classes of the same name
B: Classification Management of classes
① according to the function of
② according to the module
(3) Definition of package:
①package package name;
② multi-stage ladle. Separate
(4) Precautions:
The A:package statement must be the first in the file
B: In a Java file, there can be only one package
C: If there is no package, the default is the No bag name
(5) Compile and run with package
A: Manual Type
B: Auto-type
"Javac–d. Helloworld.java "
3. Guide Package
(1) Every time we use a class with a package, very troublesome, this time provides a keyword
(2) Format:
A:import Package Name: class name; "Recommended"
B:import Registration: *;
(3) Order of Package,import,class
Package > Import > Class
"The package statement must be the first executable code of the member"
"Package statement can only have one in a Java file"
"If there is no package, default means no packages name"
4. Permission modifiers
5. Common modifiers
(1) Classification:
A: Permission modifier: public,protected, default, private
B: State modifier: static,final
C: Abstraction modifier: Abstract
(2) A common class is a modifier of its composition
A: Class
① default: Public, Final,abstract
② Common: Public
B: Member variables
① default: public,protected, Default, private,static,final
② Common: Private
C: Construction method
① default: public,protected, default, private
② Common: Public
C: Member Method
① default: public,protected, Default, Private,static,final,abstract
② Common: Public
(3) The other more common
public static final int X = 10;//static constant
public static void Show () {};//static method
Public final void Show () {};//The method cannot be overridden
public abstract void Show ();//abstract method
Java Series Learning (10)-Package and permission modifiers