收到“不能让一个静态参考非静态方法”的错误，但我还没有宣布我是从静态

Question

调用方法时我试图编译我得到的错误：

cannot make a static reference to the non-static method getId() from the type Doctor.

Doctor是Staff的子类。当我在代码中将Doctor替换为Staff时，我得到同样的错误。我知道我不能用一个超类替代一个子类，所以这就是为什么Staff不会工作，但在我的Database类中，我没有声明任何东西是静态的，所以我不明白它为什么或者它是静态的为什么我得到这个错误。

这是我的数据库类

import java.util.ArrayList; 


public class Database 
{ 
String id; 

private ArrayList<Staff> staff; 

/** 
* Construct an empty Database. 
*/ 
public Database() 
{ 
    staff = new ArrayList<Staff>(); 
} 

/** 
* Add an item to the database. 
* @param theItem The item to be added. 
*/ 
public void addStaff(Staff staffMember) 
{ 
    staff.add(staffMember); 
} 

/** 
* Print a list of all currently stored items to the 
* text terminal. 
*/ 
public void list() 
{ 
    for(Staff s : staff) { 
     s.print(); 
     System.out.println(); // empty line between items 
    } 
} 

public void printStaff() 
{ 
    for(Staff s : staff){ 


     id = Doctor.getId();//This is where I'm getting the error. 


     if(true) 
     { 
      s.print(); 
     } 
    } 
} 

这是我的工作人员类。

public class Staff 
{ 
    private String name; 
    private int staffNumber; 
    private String office; 
    private String id; 

/** 
* Initialise the fields of the item. 
* @param theName The name of this member of staff. 
* @param theStaffNumber The number of this member of staff. 
* @param theOffice The office of this member of staff. 
*/ 
public Staff(String staffId, String theName, int theStaffNumber, String theOffice) 
{ 
    id = staffId; 
    name = theName; 
    staffNumber = theStaffNumber; 
    office = theOffice; 
} 

public String getId() 
{ 
    return this.id; 
} 


/** 
* Print details about this member of staff to the text terminal. 
*/ 
public void print() 
{ 
    System.out.println("ID: " + id); 
    System.out.println("Name: " + name); 
    System.out.println("Staff Number: " + staffNumber); 
    System.out.println("Office: " + office); 

} 

}

Answer 1

你调用该方法，就好像它是静态的，因为你正在使用的类名调用它：Doctor.getId()。

您需要调用实例方法的类Doctor的实例。

也许你打算在循环中的s（员工实例）上拨打getId？