Several points to note in Java

I have been learning Java for a while, and I think it is important to have some basic knowledge, so I wrote it down and shared it. If you don’t like it, don’t comment.

1. Identifier

(1) Definition: In the Java language, the character sequence

# used when naming classes, methods, variables, packages, parameters, etc. ## (2) Contents included: 0-9, a-z, A-Z, &, _

(3) Rules to note: 1. Composed of letters, numbers, underscores and dollar signs

2. Can't start with numbers

3. Differential cases

4. The length is unlimited (but it is recommended not to exceed 15 characters)

## 5. Java keywords and reserved words

(4) Naming specifications: 1. Camel case naming: a. Class name: first letter capitalized

b. Method name: first letter lowercase

)

　　　　 2. See the name and know the meaning

　　 　　 3. The length is recommended not to exceed 15 characters

2. this keyword and super keyword

（ 1) this:

a. Used to specify the object of this class, which can access the properties and methods of this class

b. Used to refer to the constructor of this class, used for the constructor calls between (must be placed on the first line)

(2)super:

　　a. Used to specify the object of the parent class, and can access the properties and methods of the parent class

　b. Used to refer to the constructor of the parent class, used for calls between constructors (must be placed on the first line)

　#: Since this and super are used to refer to the constructor, Both must be placed on the first line, so they cannot coexist in this case

3. Overloading and rewriting

4. Abstract classes and ordinary Class

　　(1) Same: both are used to describe things, and they can define properties, methods, and constructors

　　(2) Different: 1. Ordinary classes cannot define abstract methods, while Abstract classes can

　　　　 2. Ordinary classes can be instantiated, but abstract classes cannot Write

5. Contact between abstract class and interface

(1): When the methods in the abstract class are all abstract methods, it becomes an interface

(2) Comparison: A. Abstract classes are used for inheritance, and are single inheritance

　　 Interfaces are used for implementation, and can be implemented in multiple ways

　　B. Non-abstract methods can be defined in abstract classes and provided directly to children Class usage

　　　　 The interfaces are all abstract methods, which must be implemented by subclasses

------------Okay, let’s sort this out first, and then we’ll discuss it later Then write. ---------------

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