将对象添加到LinkedList Java数组

Question

So I'm working with hashing and want to create an array of LinkedList. How do you add the new Object to the LinkedList using the table[index]. This is what I have so far, but when I try to call the LinkedList method add it doesn't work. Is it because everything is set to null beforehand? Do I need to add everything manually?

private void populateLinkedList(LinkedList<String>[] table, ArrayList<String> dictionary){
    for(String s:dictionary){
        String temp=findHash(s);
        System.out.print(temp + ": ");
        int hashKey=hashFunction(temp);
        Anagram obj=new Anagram(s, temp, hashKey);
                    table[hashKey].add(obj);
    }       
}

populateLinkedList(hashTable, dictionaryList); This is how I call the function.

Answer 1

An array cannot have a component type that is a parametrized type, or I should say its not useful. Basically due to type erasure, the type of the array is not known, which causes the array store check to fail.

LinkedList<String>[] table is causing your issue. The argument passed into the method cannot be of type LinkedList<String>[] because its impossible to instantiate such a type in Java.

Try the following line in your IDE, which won't compile:

LinkedList<String>[] list = new LinkedList<String>[];

Try using a:

List<LinkedList<String>> instead of LinkedList<String>[]

See the Generic Faq

Working Example

I had to stub a bunch of methods, but here is a working example:

import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;

public class ArrayStoreCheck {

    public static void main(String[] args) {
        List<LinkedList<Anagram>> lists = new ArrayList<LinkedList<Anagram>>();
        LinkedList<Anagram> anagrams = new LinkedList<Anagram>();
        lists.add(anagrams);

        List<String> dictionary = new ArrayList<String>();
        dictionary.add("one");
        dictionary.add("two");

        populateLinkedList(lists, dictionary);

        System.out.println(lists.get(0).get(0));
    }

    private static void populateLinkedList(List<LinkedList<Anagram>> table, List<String> dictionary){
        for(String s:dictionary){
            String temp=findHash(s);
            int hashKey=hashFunction(temp);
            Anagram obj=new Anagram(s, temp, hashKey);
            table.get(hashKey).add(obj);
        }       
    }

    //Stub
    private static String findHash(String s){
        return "";
    }

    //Stub
    private static int hashFunction(String s){
        return 0;
    }

    //Stub
    public static class Anagram{

        private String s;

        public Anagram(String s, String t, int key){
            this.s = s;
        }

        @Override
        public String toString() {
            return s;
        }       
    }
}

Answer 2

You really can't do

 int hashKey=hashFunction(temp);
 .... 
 table[hashKey].add(obj);

assuming the hashKey value is something that can be MIN to MAX integer value. You can only access elements of an array with a value that is 0 to array.length . What exception are you getting?

But I think the main problem is that you are attempting to add an Anagram type to the LinkedList which is expecting a String .

You definitely need to make sure there is an instance of LinkedList at any index you are attempting to access.