function to return a string in java
public String time_to_string(long t) // time in milliseconds
{
    String ans;
    int mins,secs;
    if (t < 0)
    {
        return "-";
    }
    else
    {
        secs = (int)(t/1000);
        mins = secs/60;
        secs = secs - (mins * 60);

        ans = ""+mins+":"+String.format("%02d", secs);

        return ans;
    }
}

public String time_to_string(long t) // time in milliseconds
{
    if (t < 0)
    {
        return "-";
    }
    else
    {
        int secs = (int)(t/1000);
        int mins = secs/60;
        secs = secs - (mins * 60);
        return String.format("%d:%02d", mins, secs);
    }
}

return String.format("%d:%d", mins, secs);