Java-抽象类，equals()和两个子类 [英] Java - abstract class, equals(), and two subclasses

问题描述

我有一个名为 Xpto 的抽象类，以及两个扩展了它的子类，名为 Person 和 Car .我还有一个名为main的 Test 类和一个方法 foo()，该方法验证两个人或汽车(或扩展Xpto的类的任何对象)是否在等于.因此，我在Person和Car类中都重新定义了 equals().两个人的名字相同，两个人的名字相同，两辆车的名字相同，则两个人的名字相等.

I have an abstract class named Xpto and two subclasses that extend it named Person and Car. I have also a class named Test with main() and a method foo() that verifies if two persons or cars (or any object of a class that extends Xpto) are equals. Thus, I redefined equals() in both Person and Car classes. Two persons are equal when they have the same name and two cars are equal when they have the same registration.

但是，当我在Test类中调用foo()时，总是得到"false".我明白为什么:在Xpto抽象类中未重新定义equals().那么...如何在该foo()方法中比较两个人或两个汽车(或扩展Xpto的类的任何对象)?

However, when I call foo() in the Test class I always get "false". I understand why: the equals() is not redefined in Xpto abstract class. So... how can I compare two persons or cars (or any object of a class that extends Xpto) in that foo() method?

总而言之，这是我的代码:

In summary, this is the code I have:

public  abstract class Xpto {


}

public class Person extends Xpto{

        protected String name;

        public Person(String name){
                this.name = name;
        }

        public boolean equals(Person p){
                System.out.println("Person equals()?");
                return this.name.compareTo(p.name) == 0 ? true : false;
        }
}

public class Car extends Xpto{
        protected String registration;

        public Car(String registration){
                this.registration = registration;
        }

        public boolean equals(Car car){
                System.out.println("Car equals()?");
                return this.registration.compareTo(car.registration) == 0 ? true : false;
        }
}

public class Teste {

        public static void foo(Xpto xpto1, Xpto xpto2){
                if(xpto1.equals(xpto2))
                        System.out.println("xpto1.equals(xpto2) -> true");
                else
                        System.out.println("xpto1.equals(xpto2) -> false");

        }

        public static void main(String argv[]){
                Car c1 = new Car("ABC");
                Car c2 = new Car("DEF");
                Person p1 = new Person("Manel");
                Person p2 = new Person("Manel");

                foo(p1,p2);
        }
}

推荐答案

正如其他人所说，您重写的方法的签名必须完全相同.覆盖方法时，为确保覆盖，请使用函数上方的 @Override 批注，因此，如果您更改了方法，则Eclipse之类的IDE会发出警告.

As the others say, the signature of the method you override must be exactly the same. When overriding methods, to make sure you are overriding, use the @Override annotation above the function, so IDEs like Eclipse will warn you if you changed the method.

是这样的:

@Override
public boolean equals(Object obj){
...Your code here...
}

我建议也覆盖 hashCode()，因为在将项目插入列表，集合，hastables等中以实现相等(并执行)时， hashCode()>被使用(有时不是 equals()！)

I would suggest to override hashCode() as well because when inserting items into lists, sets, hastables, etc... for equality (and performande) hashCode() is used (and sometimes equals() is not!)

因此，您的最终代码将是:

So your final code would be:

@Override
public boolean equals(Object obj){
...Your code here...
}

@Override
public int hashCode(){
...Your code here...
}

更多信息，请参见 javadoc

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