有没有一种方法可以一起在Java中使用构造函数和突变器

Question

目前，代码不完整，但是我想知道是否可以使用构造函数在突变器内制造的字符串partno。

public static class Invoice{
    Scanner sam = new Scanner(System.in);
    int Quality;
    double price;
    public Invoice(){ 
        
    }
    public Invoice(String partNo, String description) { 
    }
    public void setPartNo() {
        System.out.println("Enter part no: ");
        String partNo  = sam.nextLine();
        
    
    }
    public static String getPartNo() {
        return Invoice.getPartNo();
        
    }
        }
    

    public static void main(String[] args) {
      Invoice.getPartNo();

Answer 1

public static class Invoice{
    Scanner sam = new Scanner(System.in);
int Quality;
double price;
public Invoice(){ 
    
}
public Invoice(String partNo, String description) { 
}
public void setPartNo() {
    System.out.println("Enter part no: ");
    String partNo  = sam.nextLine();
    

}
public static String getPartNo() {
    return Invoice.getPartNo();
    
}
    }


public static void main(String[] args) {
  Invoice.getPartNo();

您在这里有一些构造函数的参数，您什么都不做，这是毫无意义的。构造函数完成执行后，它们将不再存在，因此您的突变器不可能将

这些参数获取，将它们设置为实例成员，这样您的突变器也可以访问它们。

public static class Invoice {
  Scanner sam = new Scanner(System.in);
  int quality;
  double price;

  // add the additional instance members
  String partNo;
  String description;

  public Invoice() { }

  public Invoice(String partNo, String description) {
    this.partNo = partNo;
    this.description = description;
  }

  // a normal mutator (setter) will not use a Scanner, but accept the value as parameter
  // but for now, I'm keeping your original design
  public void setPartNo() {
    System.out.println("Enter part no: ");
    this.partNo = sam.nextLine(); 
    // again, use this.partNo. If you declare it as a String here, it will no longer exist when the method is finished
  }

  // this getter is both pointless, and will cause trouble by creating an endless 
  // recursive loop. Delete it.
  public static String getPartNo() {
    return Invoice.getPartNo();
  }
}

现在，相同的代码具有一些改进：

public static class Invoice {
  int quality;
  double price;

  // add the additional instance members
  String partNo;
  String description;

  public Invoice() { }

  public Invoice(String partNo, String description) {
    this.partNo = partNo;
    this.description = description;
  }

  public void setPartNo(String partNo) {
    // you can always add validation on the new value here
    this.partNo = partNo;
  }

  public String getPartNo() {
    return partNo;
  }
}

这是您可以使用的：

public static void main(String[] args) {
  Invoice in = new Invoice("part", "description");
  System.out.pintln(in.getPartNo());
  in.setPartNo("new PartNo");
  System.out.println(in.getPartNo());
}

如果您想知道您的Getter是否应该是静态的：
仅当字段本身是静态时，它才应该是静态的。由于您通过传递给构造函数的参数设置值，因此可疑它应该是静态的。

构造函数的参数应（通常）仅设置该特定实例的值。
如果是静态字段，则将为该类型的每个实例设置。