“在抽象类中没有默认构造函数”

Question

我得到了一个没有默认构造函数可用的错误，只有一个具体类实现了相同的抽象类，我不知道为什么，任何帮助都非常感谢。

`

public abstract class Employee implements Payable 
    private String firstName; 
    private String lastName; 
    private String socialSecurityNumber; 
    private date birthdate; 

      // constructor 
      public Employee(String firstName, String lastName, 
      String social, date dob) 
      { 
      this.firstName = firstName; 
      this.lastName = lastName; 
      this.socialSecurityNumber = social; 
      //this.birthdate = getBirthdate(); 
       // Birthdate(year, month, day); 
       birthdate = dob; 
      } 



public class pieceWorker extends Employee // no default constructor available 
{ 
    private double wage; `` 
    private int pieces; 


    public void pieceWorker(String firstName, String lastName, String social,date dob, double wage, int pieces) // use some getters ? 
    { 
     super(firstName,lastName,social, dob); 
     setWage(wage); 
     setPieces(pieces); 
     this.wage = wage; 
     this.pieces = pieces; 
    } 

Answer 1

您所指定的void返回类型为构造函数。因为构造函数不能有返回类型，所以你会得到这个错误，因为你没有真正定义一个构造函数，它只是一个常规方法。 你需要从你的方法pieceWorker删除void使它成为一个构造函数，像这样：

public pieceWorker(String firstName, String lastName, String social,Date dob, double wage, int pieces) 
    { 
     super(firstName,lastName,social, dob); 
     setWage(wage); 
     setPieces(pieces); 
     this.wage = wage; 
     this.pieces = pieces; 
    } 

而且，除非date是你创建一个类时，你可能想将其更改为Date，在java.util包中。

Answer 2

由于在父级抽象类中没有缺省（或无参数）构造函数，因此必须指定子类中使用的构造函数。

在子类中，您没有指定构造函数，因为您添加了返回类型void。请修改代码如下。

public abstract class Employee implements Payable 
    private String firstName; 
    private String lastName; 
    private String socialSecurityNumber; 
    private date birthdate; 

      // constructor 
      public Employee(String firstName, String lastName, 
      String social, date dob) 
      { 
      this.firstName = firstName; 
      this.lastName = lastName; 
      this.socialSecurityNumber = social; 
      //this.birthdate = getBirthdate(); 
       // Birthdate(year, month, day); 
       birthdate = dob; 
      } 



public class pieceWorker extends Employee // no default constructor available 
{ 
    private double wage; 
    private int pieces; 


    public pieceWorker(String firstName, String lastName, String social,date dob, double wage, int pieces) // use some getters ? 
    { 
     super(firstName,lastName,social, dob); 
     setWage(wage); 
     setPieces(pieces); 
     this.wage = wage; 
     this.pieces = pieces; 
    } 
} 

Answer 3

如所提到的由@Gulllie和@dammina（几乎在同一时间），类pieceWorker是具有方法

public void pieceWorker(args...) 

，而不是一个构造函数。因此，类pieceWorker将使用默认的构造函数。 任何构造函数的第一行是调用super（）。如果你没有明确地调用super（），java会为你做。

public abstract class Employee implements Payable{ 
private String firstName; 
private String lastName; 
private String socialSecurityNumber; 
private date birthdate; 

     // constructor 
     public Employee(String firstName, String lastName, 
     String social, date dob) 
     { 
     this.firstName = firstName; 
     this.lastName = lastName; 
     this.socialSecurityNumber = social; 
     //this.birthdate = getBirthdate(); 
      // Birthdate(year, month, day); 
      birthdate = dob; 
     } 
} 

您没有上述抽象类中的默认构造函数，因为您已经定义了自己的构造函数。 编译器将对您的pieceWorker类进行以下修改。

public class pieceWorker extends Employee // no default constructor available 
{ 
private double wage; 
private int pieces; 

// compiler will insert following constructor 
public pieceWorker(){ 
    super(); 
} 

public void pieceWorker(String firstName, String lastName, String social,date dob, double wage, int pieces) // use some getters ? 
{ 
    super(firstName,lastName,social, dob); 
    setWage(wage); 
    setPieces(pieces); 
    this.wage = wage; 
    this.pieces = pieces; 
} 
} 

，你可以做以下让你的代码工作：

public class pieceWorker extends Employee // no default constructor available 
{ 
private double wage; 
private int pieces; 

public pieceWorker(String firstName, String lastName, String social,date dob, double wage, int pieces) // use some getters ? 
{ 
    super(firstName,lastName,social, dob); 
    setWage(wage); 
    setPieces(pieces); 
    this.wage = wage; 
    this.pieces = pieces; 
} 
}