The constructor method under Java inheritance relationship calls the implementation method

This article mainly introduces the relevant information on the detailed explanation of constructor method calls under Java inheritance relationship. I hope this article can help everyone understand and master this part of the content. Friends in need can refer to it

Detailed explanation of the constructor call under Java inheritance relationship

When creating an object of a class in Java, if the class has a parent class, the constructor method of the parent class is called first, and then called Subclass constructor. If the parent class does not define a constructor, the default constructor without parameters automatically created by the compiler is called. If the parent class defines a public parameterless constructor, the parameterless constructor will be automatically called before calling the child class's constructor. If the parent class only has a parameterized constructor and no parameterless constructor, the subclass must explicitly call super (parameter list) in the constructor to specify a parameterized constructor. If the parent class defines a parameterless constructor, but the parameterless constructor is declared as private, the subclass must also explicitly call super (parameter list) in the constructor to specify a parameterized constructor. If the parent class has no other parameterized constructor, the subclass cannot be created.

##SubclassPublic no-parameter constructorPrivate no-parameter constructorPublic no-parameter constructorNoneNoneNoneAll constructors will call the default constructor of the parent classYesNoneNoneAll constructors will call the defined parameterless constructorNoneNoneYesAll constructors must specify to call a constructor with parameters, or call some other constructor through this. Yes No Yes You can specify to call a certain constructor. If not specified, the no-argument constructor will be called. method. NoneYesNoneSubclass cannot be constructed (parent class cannot derive subclass)NoneYesYesAll constructors must specify to call a constructor with parameters, or call some other constructor through this construction method.

There is a parent class

For example:

class Parent {
  private String pString;
  Parent(){
    pString = "p1";
  }
}

class Child extends Parent {
  private String cString;
  Child() {
    cString = "c1";
  }
}

When the Child object is created, the constructor of the parent class Parent will first be called to convert pString Initialize it to "p1", and then call Child's constructor to initialize cString to "c1".

class Parent {
  private String pString;
  private Parent(){
    pString = "p1";
  }
  Parent(String s){
    pString = "p2";
  }
}

class Child extends Parent {
  private String cString;
  Child() {
    super("");
    cString = "c1";
  }
}

Since the parent class defines a private parameterless constructor, you must explicitly specify to call a parameterized constructor in the subclass.

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