我如何同时表示应该是2个不同类的对象

Question

Today I had test in OOP and I was given the following task to code:

Imagine you have two classes: Employee (which represents being an employee) and Ninja (which represents being a Ninja). An Employee has both state and behaviour; a Ninja has only behavior. You need to represent an employee who is also a ninja (a common problem in the real world). By creating only one interface and only one class (NinjaEmployee), show how you can do this without having to copy method implementation code from either of the original classes. Test your code in main method

I did not really understand the problem well, but this is the solution I came with (I know it's not what was asked):

I created 4 classes except main. As Employee has state and behaviour I came up with this code:

public class Employee {
    private int ID;
    private String Name;
    private double salary;

    public Employee(int ID, String Name, double salary) {
        this.ID = ID;
        this.Name = Name;
        this.salary = salary;
    }

    public int getID() {
        return ID;
    }

    public void setID(int ID) {
        this.ID = ID;
    }

    public String getName() {
        return Name;
    }

    public void setName(String Name) {
        this.Name = Name;
    }

    public double getSalary() {
        return salary;
    }

    public void setSalary(double salary) {
        this.salary = salary;
    }

    public void startWorking() {
        System.out.println("Started Working");
    }
}

Class ninja has only behaviour:

public class Ninja {

    public Ninja(){}


    public void moveNinja(){
        System.out.println("Ninja moved");
    }
}

Class NinjaEmployee:

public class NinjaEmployee extends Employee implements MyInterface {

    public NinjaEmployee(int ID, String Name, double salary) {
        super(ID, Name, salary);
    }

    public void moveNinja() {
        System.out.println("Ninja Moved");
    }

}

Interface which does not make sense in my code:

public interface MyInterface {

   public void moveNinja();
   public void startWorking();

}

Main class:

public static void main(String[] args){
    MyInterface em = new NinjaEmployee(123,"Sandro",1000000);
    em.moveNinja();
    em.startWorking();
}

My question is following:

1) Specifically/Technically what was asked in test?

2) What would be correct approach/code for given problem?

Answer 1

I don't know correct answer (task is kinda not very strictly defined, there is some unclear moments), but i would do something like this:

public interface IAmNinja {
   public void moveNinja();
}

public interface IAmEmployer {
   public void startWorking();
}

public class NinjaEmployee implements IAmNinja, IAmEmployer {
    private Ninja _ninja;
    private Employer _employer;

    public NinjaEmployee(int ID, String Name, double salary) {
        _employer = new Employer(ID, Name, salary);
        _ninja = new Ninja();
    }

    public void moveNinja() {
        _ninja.moveNinja();
    }

    public void startWorking() {
        _employer.startWorking();
    }
}

Answer 2

Nice question.
The key point of the question is:

1. we should use one interface.
2. Ninja class should have some methods (not attributes).

So we should try to use these key point.

I provide a class diagram below:

First of all: We have Employee class and implement it like other simple classes. It has some implemented attributes and classes.

Secondly : We have an Interface named Ninja_Interface that have some method declarations about ninja. ( moveNinja1 and moveNinja2 )

Thirdly : Ninja Class that implemented (or Realized) Nijna_Interface and have some implementation of any method declarations in Ninja_Interface .

Fourthly : the NinjaEmployee class. It inherited from Employee . So it has all Employee 's attributes and methods. Also it implements Ninja_Interface . So it should implements all Ninja_Interface methods declarations. On the other hand, NinjaEmployee have an instance of Ninja (notice that Ninja class implements all Ninja_Interface methods).
So , In Ninja_Employee class, in implementation of Ninja_Interface methods, we can use Ninja instance methods to call.

For example some parts of NinjaEmployee is like below code:

private Ninja ninja=new Ninja();
public void moveNinja1()
{
    ninja.moveNinja1();
}
public void moveNinja2()
{
    ninja.moveNinja2();
}

Main question is: why Ninja class should have only some methods ?
It is because of Ninja class is just the implementations of Ninja_Interface methods and there no need to have attributes. So instances of Ninja class are the same . So we can declare Ninja attribute in NinjaEmployee as static attribute .

Finally : we can add some attributes of ninja into NinjaEmployee class too.

Answer 3

You cant create 1 object of 2 class es You can extend class so whenever child class is instantiated it calls parent class constructor Then You can create object of another class in that constructor

Add employees in array and add option to add employee in ninja? 1.yes or 2.no? if yes , add to ninja..then in main method print names of ninja using for loop one by one