有没有办法使默认的NSDragOperation Move仍然允许复制？(Is there a way to make the default NSDragOperation Move and still allow Copy?)

 如果您尝试将食物添加到课程中，则应使用“拥有”关系，例如： 
 
public class Course {
    private Food food;

    public Course(Food food) {
        this.food = food;
    }

    public Course() {

    }

    public Food getFood() {
        return this.food;
    }

    public void setFood(Food food) {
        this.food = food;
    }
}
 
 我也不会使用StarterFood扩展一个Course，因为extends是for和“ 是一个 ”关系，我称之为StarterCourse，然后在构造函数中为该课程添加默认食物。 
 
public class StarterCourse extends Course {

    public StarterCourse(Food food) {
        // here call the super classes constructor
        // add items via the Course constructor
        super(food);
    }
}
 
 然后在你的主类中测试它试试这个： 
 
public class Main() {
    public static void main() {
        // First create new Food object
        Food food = new Food(); 
        // Create a new StarterCourse and add the Food object to it
        StarterCourse starterCourse = new StarterCourse(food);
    }
}

If your trying to add a Food to a Course, you should use a "has a" relationship for example:
 
public class Course {
    private Food food;

    public Course(Food food) {
        this.food = food;
    }

    public Course() {

    }

    public Food getFood() {
        return this.food;
    }

    public void setFood(Food food) {
        this.food = food;
    }
}
 
I also wouldn't use StarterFood to extend a Course, because extends is for and "is a" relationship, I would call it StarterCourse and then add a default food for that course in the constructor.
 
public class StarterCourse extends Course {

    public StarterCourse(Food food) {
        // here call the super classes constructor
        // add items via the Course constructor
        super(food);
    }
}
 
Then in your main class to test it out try this:
 
public class Main() {
    public static void main() {
        // First create new Food object
        Food food = new Food(); 
        // Create a new StarterCourse and add the Food object to it
        StarterCourse starterCourse = new StarterCourse(food);
    }
}