当它们相同时，如何在ArrayList中找到多个对象的索引

Question

In this I am storing words in one arraylist and the respective phone-number that corresponds to it in another arraylist. I want to be able to enter a number and return all words in the other list that correspond. I have my arraylists setup like this.

List<String> listWords = new ArrayList<String>(); // An ArrayList which stores all added words.
List<String> listNum = new ArrayList<String>();// An ArrayList which stores all phone numbers that correspond to all the added words

The words are converted as they would on a phone keypad (ie 2 = a,b,c 3 = d,e,f etc).

Also I am adding the words simply like this;

public void readWords() 
{
    PhoneWords ph = new PhoneWords();
    try
    {
        // Open the file that is the first 
        // command line parameter
        FileInputStream fstream = new FileInputStream("words.txt");

        BufferedReader br = new BufferedReader(new InputStreamReader(fstream));
        String strLine;

        //Read File Line By Line
        while ((strLine = br.readLine()) != null)   
        {
            String phNum = ph.word2Num(strLine);
            listWords.add(position, strLine);
            listNum.add(position, phNum);
            position++; // index position, only used when initally adding the words
        }

    }catch (Exception e)
    {
        //Catch exception if any
        System.err.println("Error: " + e.getMessage());
    }

Answer 1

In your case I would rather use the following data structure that maps a phone number to a list of words

HashMap<String, List<String>> phoneNumbersMap = new HashMap<String, List<String>>();

Reference for HashMap is here http://docs.oracle.com/javase/6/docs/api/java/util/HashMap.html

It will also make retrieving the words much faster if your list grows in the future!

To add data to the HashMap you can do:

if (map.containsKey(phNum)) {
    List<String> words = map.get(phNum);
    words.add(strLine);
} else {
    List<String> words = new ArrayList<String>();
    words.add(strLine);
    map.put(phNum, words);
}