Getting instance of class X from an ArrayList of class X without position

Question

If I have an ArrayList in a Java 6 program as follows:

ArrayList<Keyword> = new ArrayList<Keyword>();

Where a Keyword has an int keywordNo, String text, int frequency and a few other fields.

How can I retrieve an element from the ArrayList if I know the keywordText but not the position of the element or the value of field keywordNo?

I know that I could use a loop and simply read through the ArrayList comparing Strings until I find the element but is there any better alternative?

Would it be possible to have more than one Keyword object matching a given keywordText? — Tim Biegeleisen
– Tim Biegeleisen, Commented Apr 30, 2015 at 22:46
The List interface has an indexOf() method which returns the index of a given input Object, but it uses the equals() method which might not work for your case if the other fields in a Keyword be unknown. — Tim Biegeleisen
– Tim Biegeleisen, Commented Apr 30, 2015 at 22:56
I would rather avoid writing my own dedicated equals method for the class in question. — Mr Morgan
– Mr Morgan, Commented Apr 30, 2015 at 22:58

bhspencer · Accepted Answer · 2015-04-30 22:54:17Z

2

You would have to iterate over every element in the list with a loop. For each iteration you will need to get the current element and check its value.

For faster access you should use a Map<String, Keyword> where the String is the keywordText.

You can put your keywords in a Map like this:

Map<String, Keyword> keywordsMap = new HashMap<String, Keyword>();
for (Keyword k : keywordList) {
    keywordsMap.put(k.text, k);
}

Then if you want to access a particular Keyword you can make a call like this:

Keyword result = keywordsMap.get("somekeyword");

edited Apr 30, 2015 at 22:54

answered Apr 30, 2015 at 22:47

bhspencer

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3 Comments

Tim Biegeleisen Over a year ago

And q.v. this SO post which also came to the same conclusion.

Mr Morgan Over a year ago

Yes, this is just what I think I will have to do.

Mr Morgan Over a year ago

And have a break statement in the loop as well.

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