具有 getter 和 setter 方法的 Java 对象

Question

Hi can someone please help me,I am a novice programmer and I don't understand the following code.

How does one.bark() automatically returns the statement under the first if condition. How does the compiler know which if statement to display (because we are not passing the size while calling bark() )? I know the object calls the function setSize and passes the argument 70 to it. Does that mean that the value 70 becomes an attribute of the object one ?

Code:

class GoodDog {
    private int size;

    public void setSize(int s) {
        size = s;
    }

    public int getSize() 
    {
        return size;
    }

    void bark()
    {
        if (size > 60)
        {
            System.out.println("Wooof! Wooof!");
        } 
        else if (size > 14) 
        {
            System.out.println("Ruff! Ruff!");
        }
        else
        {
            System.out.println("Yip! Yip!");
        }
    }

}

class GoodDogTestDrive
{
    public static void main (String[] args) 
    {
        GoodDog one = new GoodDog();
        one.setSize(70);
        GoodDog two = new GoodDog();
        two.setSize(8);

        System.out.println("Dog one: " + one.getSize());
        System.out.println("Dog two: " + two.getSize());
        one.bark();
        two.bark();
    }

}

Answer 1

Yes. When you call one.setSize(70) , the size variable is saved as 70 in the one object. When you call one.bark() , size is still 70

Answer 2

When creating an object of a class , the object receives a copy of all non-static members of the class.

GoodDog one = new GoodDog();

object one contains a special copy of size. Like wise object two will have its own copy of member variable size.

When you set the size using setSize() function , the one object's size variable is modified and will contain the same value until another value is assigned.

When you call the bark function using one function , it's own copy of size variable is taken and used inside the bark function.

Answer 3

Actually, 70 is not a new attribute, but the size attribute takes the value 70 .

And since you have two distinct instances ( Dog one and Dog two ) of GoodDog, each one has it's own attribute size , which has it's own value (in this case 70 and 8 ).

From there, when you call the bark method, each instance ( one / two ) will check the if/else statement according to it's own attribute's value (respectively 70 / 8 ).