Question

package animal;

class AnimalHumanDogDemo
{
    public static void main(String[] args)
    {
        Animal chicken = new Animal(1.53, 53.2, 14.2, "red junglefowl");

        Human Alex = new Human(1.73, 62.3, 52.0, "Ape", "Greek", "Programmer", 1234);

        Dog Betty = new Dog(0.53, 21.6, 8.3, "wolf", "chiouaoua", 214, false, "white");

        String a = chicken.toString();

        System.out.println(a);

        double b = Alex.Yearly_salary();
        System.out.println(b);

        String c = Alex.toString();
        System.out.println(c);

        Boolean d = Betty.Expensive_Purebred();
        System.out.println(d);

        String e = Betty.toString();
        System.out.println(e);
    }
}

当我运行main时，字符串和bollean变量的结果总是为null，和＆＃39; 0＆＃39;其他一切。我在动物，人类和狗类中创建了构造函数，就像我一直在做的那样。我可以提供课程＆＃39;代码如果需要。

Answer 1

您必须将变量存储在构造函数中。

public class Animal 
{
    private double x;
    private double y;
    private String des;

    public Animal(double x, double y, String des)
    {
        this.x = x;
        this.y = y;
        this.des = des;
    }
}

如cricket_007 x = x所述，可能会导致问题。

构造函数将字段设置为默认值

1 个答案: