Java object oriented basic teaching of II
- 2021-10-16 01:45:06
- OfStack
1. Use access modifiers:
| 访问修饰符 | 同1个类中 | 同1个包中 | 子类中 | 所有类中 |
| private | √ | -- | -- | -- |
| default | √ | √ | -- | -- |
| protected | √ | √ | √ | -- |
| public | √ | √ | √ | √ |
Note:
private
Private
default
: Default
protected
Protected
public
Public
Access control level:
private→default→protected→public
2. static keyword:
Keyword: static
Members modified by static are static members, which include static code blocks, static properties, and static methods. A static member does not belong to an object, but only to the class in which the static member belongs.
Static → class
Non-static → object
Static method:
Syntax:
< Access modifier > static Return type Method name ( Parameter list ){
// Method body
}Differences between static and non-static methods:
(1) Only static members or methods can be called in static methods, but non-static members or methods cannot be called directly. If you need to call, you need to instantiate them first. (2) Static methods are methods decorated with staitc in a class that are loaded and allocated at the time the class is defined. The non-static method is a method without static keyword, which does not occupy memory when the class is defined. The non-static method is allocated memory only when the object calls the method when the class is instantiated into an object.
3. this keyword
Meaning:
The this keyword always points to the object that calls the method. When using member methods and member properties, you can use "this. Method" and "this. Member Properties" to call the method and member properties of the current object respectively.
Syntax:
this. Method name ;
this. Member attributes ;
Precautions:
1. this () cannot be used in normal methods, but can only be written in constructors
2. Must be the first statement in the constructor
Summarize
That's all for this article. I hope it can help you, and I hope you can pay more attention to this site!