java - 尝试使用我自己的比较器进行 binarySearch 时出错

Question

我正在尝试创建一个类，在其中我可以借助二进制搜索将对象快速插入到类列表中。

这是我的类和内部类:

public class PostingsList implements Iterator<PostingsEntry>{

    /** The postings list */
    private ArrayList<PostingsEntry> list = new ArrayList<PostingsEntry>();

    class PostingsEntryComparator implements Comparator{
        @Override
        public int compare(PostingsEntry pA, PostingsEntry pB){
            if(pA.docID < pB.docID){
                return -1; 
            }   
            else if(pA.docID == pB.docID){
                return 0;
            }   
            else{
                return 1;
            }   
        }   
    }     

    public void add(PostingsEntry newPostingsEntry){ 
        //put in the right place
        PostingsEntryComparator pc = new PostingsEntryComparator();
        int res = Collections.binarySearch(list, newPostingsEntry, pc);
        if(res < 0){
            list.add(-res-1, newPostingsEntry);
        }
        else{
            System.out.println("already exists");
        }
    }
}

内部类用于比较 list 的对象，以便 Collections.binarySearch 可以工作。但是，我收到此错误。这是什么意思，我该怎么办？

n180-p69:new sahandzarrinkoub$ sh compile_all.sh
ir/PostingsList.java:22: error: PostingsList.PostingsEntryComparator is not abstract and does not override abstract method compare(Object,Object) in Comparator
    class PostingsEntryComparator implements Comparator{
    ^
ir/PostingsList.java:23: error: method does not override or implement a method from a supertype
        @Override
        ^

2 errors

Answer 1

class PostingsEntryComparator implements Comparator {
    ...
}

实现“原始”Comparator接口(interface)，它接受 Object参数，即 compare(Object,Object) .但是，这不是您要覆盖的内容，因为您的比较器特定于 PostingsEntry .

因此，你需要实现Comparator<PostingsEntry> :

class PostingsEntryComparator implements Comparator<PostingsEntry> {
    ...
}