Appending text from array list to a String takes a lot of time

Question

I am reading a Simple Notepad Text file containing a lot of data actually in a 3mb of size so you can imagine the number of words it can have! The problem is I am reading this file into a string then splits the string so that I can hold each single word inside an ArrayList(String). It works fine for me but the actual problem is that I am processing this array list for some purpose and then again I have to append or you can say put all the words of array list back to the String!

so that the steps are:

I read a text file into a String (alltext)
Split all words into an arraylist
process that array list (suppose I removed all the stop words like is, am, are)
after processing on array list I want to put all the words of array list back to the string (alltext)
then I have to work with that string (alltext) (alltext is the string that must contains the text after all processing)

The problem is that at step number 4 it takes a lot of time to append all the words back to the string my code is:

BufferedReader br = new BufferedReader(new FileReader(file));
String line = "";
while ((line = br.readLine()) != null) {
   alltext += line.trim().replaceAll("\\s+", " ") + " ";
}
br.close();

    //Adding All elements from all text to temp list            
    ArrayList<String> tempList = new ArrayList<String>();
    String[] array = alltext.split(" ");
    for (String a : array) {
        tempList.add(a);
    }

    //remove stop words here from the temp list

    //Adding File Words from List  in One String 
    alltext = "";

    for (String removed1 : tempList) {
        System.out.println("appending the text");
        alltext += removed1.toLowerCase() + " ";
        //here it is taking a lot of time suppose 5-10 minutes for a simple text file of even 1.4mb
    }

So I just want any idea so that I can reduce the time for an efficient processing and relax the machine! I will be thankful for any suggestions and ideas... Thanks

Have you profiled your code to find exacly what loop takes the most time? — Tassos Bassoukos, Apr 10 '14 at 12:25
for (String removed1 : tempList) this piece of code takes a lot of time — Java Nerd, Apr 10 '14 at 12:26

score 2 · Accepted Answer · answered Apr 10 '14 at 12:26

2

Use a StringBuffer instead of a String.

A String is immutable and thus you create a new Object everytime you append, which takes more and more time the longer your String becomes. A StringBuffer is mutable and made for cases like yours.

answered Apr 10 '14 at 12:26

LionC

3,106
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The previous time it was taking=5min and 32 seconds and after using stringbuffer or string builder the time reduced to 1 minute and 2 seconds thanks for the idea! – Java Nerd Apr 10 '14 at 13:17

score 1 · Answer 2 · edited May 23 '17 at 11:49

1

I would recommend StringBuilder According to this stringbuilder-and-stringbuffer-in-java it's faster than a StringBuffer also check if you need the ArrayList because you can iterate through the array too

edited May 23 '17 at 11:49

Community

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answered Apr 10 '14 at 12:39

0riginal

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1
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Appending text from array list to a String takes a lot of time

2 Answers2