Java_ class and Object 03_ encapsulation and private, this, super, static keywords

A Package: A member variable in a class is private, which provides a public get () or set () for a private member variable.

Benefits of Encapsulation:

I. Hide implementation details and provide a common way to access

Ii. improved reusability of the code

Iii. Improving safety

The principle of encapsulation (thought):

I. Hide content that does not need to be provided externally

II. Hide attributes, provide public methods to access them

The embodiment of encapsulation: private is a manifestation of encapsulation.

B Private:

I. is a permission modifier

II. Members can be decorated (member variables and member methods)

III. Members that are private modified can only be accessed in this class

The C this keyword: represents an object reference for the current class.

Refers to member variables and member methods in the current class .

    Private String name;      Public Static void Main (string[] args) {        this///  Error, the Main method is static and the This keyword cannot be used.      }    public  String getName () {        return// This is actually implied here.    

D Super Keyword: The identity that represents the storage space for the parent class. (It can be understood as a reference to the parent class , through which the members of the parent class can be accessed.)

E Static Keyword:

1. You can modify member variables and member methods . a static member can be called directly using the class name (interface name) or by an object of the class.

Modifier member Variable: static variable .

I. All objects in the class share a static variable.

Ii. static variables are initialized only the first time the class is used , and are no longer initialized when the class is used for the second time.

Modify Member Method: Static method.

I. static methods cannot use this with the Super keyword .

Ii. static methods can only invoke static members of the current class directly. A non-static member that wants to be called must be called through the object of the class (because the static method does not accept the implied this).

private String name;

static String num;

Direct invocation of a static method:

To invoke a static member:

Test.num = ""; Called by the class name

This.num = ""; Error, the static decorated member method (that is, still method) cannot use this with the Super keyword

num = ""; is equivalent to Test.num = "";

You can also call through the object of the class

To invoke a non-static member:

THIS.name = ""; Error, static decorated member method cannot use this with the Super keyword

Test.name = ""; Error, name is not static

name = ""; Error, name is not static, so it is equivalent to THIS.name

Can only be called from an object of the class

Direct invocation of non-static methods:

To invoke a static member:

Test.num = "";

This.num = ""; The principle seems to be the same as above, this: is the object reference of the current class

num = ""; Call method and static method are the same principle of direct invocation

You can also call through the object of the class

Calling non-static members

Test.name = ""; Error, only static members can be called with the class name (interface name)

name = ""; Equivalent to this.name = "";

You can also call through the object of the class

Iii. a non-static method can invoke a static member directly.

2. Static characteristics:

A: Loaded with the load of the class

B: Priority and object presence

C: Shared by all objects of the class

D: Can be called by the class name:

Called by the name of the object, or by the class name, is recommended by the class name.

3. Static memory diagram: Static content in the method area

4. Static precautions;

A: There is no this object in the static method

B: Static can only access static (code tested too)

5. The difference between a static variable and a member variable

A: Belong to different

Static variable: Belongs to class, class variable

Member variables: belong to object, object variable, instance variable

B: Different memory locations

Static variables: Static area of the method area

Member Variable: heap memory

C: Different life cycle

Static variables: Static variables are loaded as the class is loaded and disappear as the class disappears

Member variables: Member variables are present as the object is created and disappear as the object disappears

D: Call Different

Static variables: Can be called by object name, or by class name

Member variable: can only be called by object name

Java_ class and Object 03_ encapsulation and private, this, super, static keywords