Java - 调用构造函数时如何使用类属性中的值

Question

I have the following problem:

1. Build the classes Animal , Cat , and Bug .
2. Define the properties color and leg_number on the relevant and necessary classes. Have them be initialized within a constructor.
3. Add the functionality that would allow us to call a method move with the Cat and Bug classes. Have the method return a string "I'm moving with leg_number legs!", with the " leg_number " being leg_number as set on the class.
4. Add a new class called Bird . Add the property wing_number . Add the functionality that would allow us to call a method move with the Bird class. Have the method return the string "I'm moving with leg_number legs!" if wing_number doesn't have an applicable value. If wing_number does have an applicable value, return the string "I'm flying".

My code thus far is as follows:

class Animal {

    protected String color;
    protected int leg_number;

    public Animal(String color, int leg_number) {
        this.color = color;
        this.leg_number = leg_number;
    }

    public void move() {
        System.out.println("I'm moving with " + leg_number + " legs!");
    }
}

class Cat extends Animal {
    String color;
    int leg_number;

    public Cat(String color, int leg_number) {
        super(color, leg_number);
        this.color = "orange";
        this.leg_number = 4;
    }

    @Override
    public void move() {
        System.out.println("I'm moving with " + leg_number + " legs!");
    }
}

class Bug extends Animal {
    String color;
    int leg_number;

    public Bug(String color, int leg_number) {
        super(color, leg_number);
        this.color = "green";
        this.leg_number = 16;
    }

    @Override
    public void move() {
        System.out.println("I'm moving with " + leg_number + " legs!");
    }
}

class Bird extends Animal {
    String color;
    int leg_number;
    int wing_number;

    public Bird(String color, int leg_number, int wing_number) {
        super(color, leg_number);
        this.color = "yellow";
        this.leg_number = 2;
        this.wing_number = wing_number;
    }

    public void move(int wing_number) {
        if (wing_number > 0) {
            System.out.println("I'm flying");
        } else {
            System.out.println("I'm moving with " + leg_number + " legs!");
        }
    }
}

I think I did what the instructions called for in setting the value for leg_number in the constructor. I'm not sure how to use it in the constructor call, though. It seems that if I have Animal myCat = new Cat("orange", 4); that I'm not following the instructions for the assignment. But I'm not sure what else to put there. I've tried using (color, leg_number) and (this.color, this.leg_number) , but as expected, they didn't work (I assume because the object hasn't been instantiated yet). I tried setting the values in the parameter list of the constructor itself, but that didn't work either. I tried having the constuctor take no parameters, but I have to call the super constructor which does require parameters, so I get an error that way.

What am I missing here?

EDIT: Where I'm trying to instantiate these is in the Main method.

Answer 1

You don't need String color and int leg_number in your sub-classes. You also don't need to override move() method in all sub-classes, except Bird . Additionally, your move() method in Bird shouldn't take any parameters but use wing_number property instead. Having said that, try the following:

class Animal {

    protected String color;
    protected int leg_number;

    public Animal(String color, int leg_number) {
        this.color = color;
        this.leg_number = leg_number;
    }

    public void move() {
        System.out.println("I'm moving with " + leg_number + " legs!");
    }
}

class Cat extends Animal {
    public Cat(String color, int leg_number) {
        super(color, leg_number);
    }
}

class Bug extends Animal {
    public Bug(String color, int leg_number) {
        super(color, leg_number);
    }
}

class Bird extends Animal {
    private int wing_number;

    public Bird(String color, int leg_number, int wing_number) {
        super(color, leg_number);
        this.wing_number = wing_number;
    }

    @Override
    public void move() {
        if (wing_number > 0) {
            System.out.println("I'm flying");
        } else {
            super.move();
        }
    }
}