从Java中的arrayList中删除项目

Question

I have a program that takes input from a file, saves each word in the file as a token and then adds each token to an array list.

The problem is that the arrayList comes up as for example ["cat","dog"," "," ","bird"], and I don't want the spaces in the arrayList.

And the file that is read is set up as shown below:

cat dog


bird

It is obvious that it is the blank lines cause the spaces, but the blank lines are necessary.

Anyway, my code is below:

import java.io.BufferedReader;
import java.io.DataInputStream;
import java.io.FileInputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;

public class NewMain{

public static void main(String[] args){

    try{
        FileInputStream fstream = new FileInputStream("Filename");

        //Get the object of datainputstream
        DataInputStream in = new DataInputStream(fstream);
        BufferedReader br = new BufferedReader(new InputStreamReader(in));
        String strLine;

        List<String> listOfWords = new ArrayList<String>();
       while((strLine = br.readLine()) != null){
        String [] tokens = strLine.split("\\s+");
        String [] words = tokens;
        for(String word : words){
            listOfWords.add(word);
            System.out.print(word);
            System.out.print(" ");      
        } 
        System.out.print("\n");
    }
       System.out.println(listOfWords);

        List<String> space = new ArrayList<String>();
        String[] spaces = {" "};
        space.addAll(Arrays.asList(spaces));

        editList(listOfWords,space);

        System.out.println(listOfWords);
in.close();
    }
    catch(Exception e){
        System.err.println("Error: " + e.getMessage());    
    }  
}

public static void editList(Collection<String> list1, Collection<String> list2){
    Iterator<String> it = list1.iterator();
        while(it.hasNext()){         
       if(list2.contains(it.next())) {
                it.remove();
            }  
       }
}
} 

The String[] spaces = {" "}; should remove the blank spaces, as I have tested it by removing spaces from an non-file arrayList. And the strange thing is that if I change it to String[] spaces = {"cat"}; it will remove cat from the arrayList.

Answer 1

The reason is quite obvious. A possible solution is to use this:

strLine = br.readLine().trim()

then implement your while loop as:

while (strLine != null && !strLine.isEmpty()) { //do stuff }

Answer 2

in your for loop add an if condition:

for(String word : words){
            if(!word.equals(""))  /* OR if( (word.length > 0) )*/  {
            listOfWords.add(word);
            System.out.print(word);
            System.out.print(" ");   
           }   
        } 

Answer 3

Try removing empty strings - since you split via the whitespace pattern \\s+ , you will not have " " in your list, but "" :

String[] spaces = {""};

But instead of removing them afterwards, don't add them in the first place !

if (word.length() == 0) continue;
listOfWords.add(word);

(and add any similar filters you need!)

This is not just simpler . It is also much more efficient. Removing an element from an array list costs O(n) . So the complexity of the code you used for filtering is O(n^2) (you could get this down to O(n) by copying into a second list). Not adding the elements in the first place is essentially for free; your parsing will even become a bit faster this way - still in O(n) , but faster than filter in a second step.