11-Play from zero javaweb-constructor

Supporting Video:

1. What is a constructor

2. Builder features

3. Custom constructors

4. Constructor overloading

First, what is a constructor?

　　Let's look at the following line of code

New is not like calling a method after

We call the method that is called automatically when the object is created, called the constructor

The default constructor cannot be found in the class, and the default constructor can be seen by the anti-compilation tool

As you can see, there's a way to do this after you've translated it into a byte code.

User () {

}

This is the default constructor.

When the compiler compiles the source file, a default constructor is created

If we set a default value for a field setting

The default value is actually set in the default constructor.

Second, the role of the constructor

1. Create objects that must be used with new

2. Completion of initialization of objects

　　

As you can see, the default values that we set are set in the default constructor method.

Three, the characteristics of the constructor

　The name of the ① constructor is the same as the name of the class that is currently located.
② prohibit defining return types, never use void as the return type.
③ in the constructor, you do not need to use the return statement.

If we do not write the constructor, we will create a constructor with no arguments by default.

　① conforms to the characteristics of the constructor
② No parameters
③ if the class is using public, the default constructor is also public

Iv. Custom Constructors

We can do it ourselves. Define constructors, and custom constructors conform to the constructor's characteristics

1. The constructor that we write ourselves is called a custom constructor
2. If we define the constructor ourselves, the compiler no longer creates the default constructor
3. A class has at least one constructor.
4. Creating an object is actually calling the constructor.

　　

　　　

V. Overloading of constructors

Overloading of constructors: As with overloads of methods
You can define multiple constructors, like the constructor's method name
Parameters are different, when you create an object, different constructors are called depending on the parameters

　

As you can see, a parameter is executed and a constructor is found,

When you create a constructor that uses two arguments, execute the constructor that will find two parameters.

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11-Play from zero javaweb-constructor