java 将 toString() 传递给方法

Question

我有以下代码

public class Mamman14 {


    public static void main(String[] args) {
        // TODO code application logic here
    }

    public class SortedPair < E extends Comparable < E >> {
        E Max_Element;
        E Min_Element;

        public SortedPair(E FirstElement, E SecondElemnt) throws IllegalPair {
            int Compare_Result = FirstElement.compareTo(SecondElemnt);

            if (Compare_Result == 0) {
                Max_Element = null;
                Min_Element = null;
                throw new IllegalPair(FirstElement.toString(), SecondElemnt.toString());
            } else if (Compare_Result > 0) {
                Max_Element = FirstElement;
                Min_Element = SecondElemnt;
            } else {
                Max_Element = SecondElemnt;
                Min_Element = FirstElement;

            }
        }

        public E getFirst() {
            return Max_Element;
        }

        public E getSecond() {
            return Min_Element;
        }

        @
        Override
        public String toString() {
            return String.format("%s is bigger then %s.", getFirst(), getSecond());
        }

    }

    public class IllegalPair extends Exception {
        public IllegalPair() {
            super("Elements must be different!!");
        }

        public IllegalPair(String Element) {
            super("Elements must be different!! \n However they are equal to " + Element);
        }

        public IllegalPair(String Element1, String Element2) {
            super("Elements must be different!! \n However the elements are " + Element1 + "and" +
                Element2 + "and they are equal.");
        }

    }
}

这是一个简单的程序，它比较 2 个元素并相应地在 Max_Element 和 Min_Element 中设置它们。我有两个问题:

当我写public class SortedPair <E extends Comparable<E>>时这是否意味着 SortedPair 只能接收包含compareTo 方法的可比较元素？

在线 throw new IllegalPair(FirstElement.toString(), SecondElemnt.toString())我使用元素的 toString() 方法创建一个新对象，假设元素没有 toString() 方法，正在发送什么？

谢谢。

Answer 1

When I write public class SortedPair <E extends Comparable<E>> does that mean that SortedPair can receive only comparable elements which contains the compareTo method?

这意味着你只能使用实现 Comparable 的东西作为类型参数，例如:

SortedPair<String> sp;
//         ^--- this must be a class that implements `Comparable`
//              or an interface that extends `Comparable`

...这又意味着您可以使用 Comparable 定义的方法在使用泛型类型声明的任何实例上 E .

In the line throw new IllegalPair(FirstElement.toString(), SecondElemnt.toString()) I create a new object using the toString() method of the elements, lets say the elements don't have a toString() method, what is being send?

这将使用 toString from Object ，这很无聊。 :-) 这就是文档所说的:

The toString method for class Object returns a string consisting of the name of the class of which the object is an instance, the at-sign character `@', and the unsigned hexadecimal representation of the hash code of the object. In other words, this method returns a string equal to the value of:

getClass().getName() + '@' + Integer.toHexString(hashCode())