使用 Comparable 接口对通用链表进行排序

Question

I want to sort my self implemented Linked List Using Comparable Interface with Java .I need to implement the compareTo method : Here is the code for my class ListElement :

 public class ListElement implements Comparable<ListElement> {
    public Object wert;
    public ListElement nachFolger;

    public ListElement(Object wert , ListElement nachFolger) {
        this.wert=wert;
        this.nachFolger=nachFolger;
    }

    @Override
    public int compareTo(ListElement a) {
        if(this.nachFolger.wert - a.wert) {
            return 1;
        }
        return 0;
    }
}

But I get an error , any recommendations ?

Answer 1

You are trying to subtract to references of type Object .

Your element type should implement Comparable :

public class ListElement<T extends Comparable<T>> implements Comparable<ListElement<T>> {
    public T wert;
    public ListElement<T> nachFolger;

    public ListElement(T wert, ListElement<T> nachFolger) {
        this.wert=wert;
        this.nachFolger=nachFolger;
    }

    @Override
    public int compareTo(ListElement<T> a) {
        return wert.compareTo(a.wert);
    }
}

Answer 2

In Java, subtract operation only applies to numeric literals (and auto-unboxed numeric objects). As you are trying to use it on non numeric Object type, you are getting the error. If you want to compare two wert values, you can do the following:

• Change the type to number from Object so that you can compare, eg:

   public Object wert; @Override public int compareTo(ListElement a) { return wert.compareTo(a.wert); }

• Change the type to Comparable so you can use compareTo on two wert objects

   public Comparable wert; @Override public int compareTo(ListElement a) { return wert.compareTo(a.wert); }