java子类打印参数默认值而不是赋值

Question

我正在阅读和练习以更好地理解 java 继承。当我运行下面的 Lion 类时，它打印出 0 和 null。我认为它应该打印出参数值，即 30 和 roars。我做错了什么？

public class Animal {

    int numTeeth;

    public Animal(int numTeeth) {
        numTeeth = this.numTeeth;
    }

    public int getNumTeeth() {
        return numTeeth;
    }   
    public void setNumTeeth(int numTeeth) {
        this.numTeeth = numTeeth;       
    }
}


public class Lion extends Animal {

    String sound;

    public Lion(int numTeeth, String sound) 
    {
        super(numTeeth);
        sound = this.sound;
    }

    public String getSound() {          
        return sound;
    }

    public void setSound(String sound) {        
        this.sound = sound;
    }

    public static void main(String[] args) {

        Lion simba = new Lion(30, "roars");     
        System.out.println(simba.getNumTeeth());
        System.out.println(simba.getSound());
    }
}

Answer 1

你的现场分配是错误的方式，应该是

this.numTeeth = numTeeth;

和

this.sound = sound;

否则您将字段分配给局部变量，这没有多大意义。