Java Series Learning (10)-Package and permission modifiers

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