Get preferences older than the most recent entry using java.util.prefs.Preferences.get

Question

With the java.util.prefs.Preferences API is it possible to get historic results which are older than the last entry?

eg if you had

prefs.put("key", "value1");
prefs.put("key", "value2");

return prefs.get("key");

will return "value2" Can I ever get "value1" ?

If no then what is the best alternative to achieve this functionality.

Answer 1

If anyone can do better I am happy to accept their answer, in the mean time:

import java.util.ArrayList;
import java.util.List;
import java.util.prefs.Preferences;

public class RecentStrings
{
    private final Preferences prefs;
    private final int noRecent;
    private static final int defaultNo = 10;
    private final String indexingKey;

    public RecentStrings()
    {
        this(Preferences.userRoot(), defaultNo, "r");
    }

    public RecentStrings(Preferences prefs, int noRecent, String indexingKey)
    {
        this.noRecent = noRecent;
        this.prefs = prefs;
        this.indexingKey = indexingKey;
    }

    public void setMostRecentString(String file)
    {
        if (!getAllRecentStrings().contains(file))
        {
            for (int i = noRecent-1; i >= 0; i--)
            {
                prefs.put(indexingKey+(i+1), prefs.get(indexingKey+i, ""));
            }
            prefs.put(indexingKey+0, file);
        }
        else
        {
            removeRecentString(file);
            setMostRecentString(file);
        }
    }

    private void removeRecentString(String file)
    {
        List<String> recents = getAllRecentStrings();
        recents.remove(file);
        for (int i=0; i < noRecent; i++)
        {
            String value;
            if (i < recents.size())
            {
                value = recents.get(i);
            }
            else
            {
                value = "";
            }
            prefs.put(indexingKey+i,value);
        }
    }

    public String getMostRecentString()
    {
        return prefs.get(indexingKey+0, "");
    }

    public List<String> getAllRecentStrings()
    {
        List<String> mostRecent = new ArrayList<>();
        for (int i = 0; i < 10; i++)
        {
            String value = prefs.get(indexingKey+i, "");
            if (!value.equals(""))
            {
                mostRecent.add(value);
            }
        }
        return mostRecent;
    }
}

Which also handles duplicates and keeps things from most recent to oldest.