无论发生什么情况，java实例变量都被设置为null

Question

所以我试图创建一个对象“猫”，它有名字、重量和情绪。将Cat值分配给这些变量后，它只打印名称和权重，而不打印心情。它会说：“名字：猫，体重：10磅，情绪：空”，不管情绪是否有效

我以为这可能是变异基因的问题，但我找不到任何可以解决它的方法。更进一步，继承这个“Cat”类的类的属性也有这个问题，但它的新属性没有，所以它看起来像“Name:Cat，Weight:10lbs，Mood:null，Type:short hair”。为什么会这样

public class Cat extends Animal{

//Attributes
private String mood;

//Constructors
public Cat()
{
    super();
    this.mood = "no mood yet";
}
public Cat(String aName, double aWeight, String aMood)
{
    super(aName, aWeight);
    this.setMood(aMood);
}

//Accessors
public String getMood()
{
    return this.mood;
}

//Mutators
public void setMood(String aMood)
{
    if(aMood.equalsIgnoreCase("sleepy") || aMood.equalsIgnoreCase("playful") || aMood.equalsIgnoreCase("hungry"))
    {
        this.mood = aMood;
    }
    else
    {
        System.out.println("Invalid mood.");
    }
}

//Other Methods
public String toString()
{
    return super.toString() + " | Mood: " + this.mood;
}


public class Animal {

//Attributes
private String name;
private double weight;

//Constructors
public Animal()
{
    this.name = "no name yet";
    this.weight = 0.0;
}
public Animal(String aName, double aWeight)
{
    this.setName(aName);
    this.setWeight(aWeight);
}

//Accessors
public String getName()
{
    return this.name;
}
public double getWeight()
{
    return this.weight;
}

//Mutators
public void setName(String aName)
{
    this.name = aName;
}
public void setWeight(double aWeight)
{
    if (aWeight > 0.0)
    {
        this.weight = aWeight;
    }
    else
    {
        System.out.println("Invalid weight.");
    }
}