问题
I am doing a self learning exercise to help me understand more about Java, but I am stuck at this question. I have the following txt file:
Name Hobby
Susy eat fish
Anna gardening
Billy bowling with friends
Note: name and hobby are separated by tab
What is the best way to read all the line and put it in arraylist(name,hobby). The tricky part is that
eat fish or bowling with friends
has white spaces and it must be put under one array and obviously I cannot hardcode it. Here is my current code:
public void openFile(){
try{
FileInputStream fstream = new FileInputStream("textfile.txt");
// use DataInputStream to read binary NOT text
BufferedReader br = new BufferedReader(new InputStreamReader(fstream));
ArrayList<String> names = new ArrayList<String>();
ArrayList<String> hobbies = new ArrayList<String>();
String lineJustFetched;
while ((lineJustFetched = br.readLine()) != null) {
String[] tokens = lineJustFetched.split(" \t");
I got an error:
java.lang.StringIndexOutOfBoundsException: String index out of range: -1
I suspect counting the index is not very useful on a tab. Any idea?
回答1:
Alright, you need to do the recipe shown below:
- Create a
BufferedReader - Create an
ArrayList<String> - Start reading data into a
Stringvariable namedlineJustFetched. - Split the
Stringby callinglineJustFetched.split("\t"); - Iterate over the
String[]produced. Check if the token you want to enter into theArrayListis not"" - If not, add the word to the
ArrayList
You specify that you need to split based on \t values so white spaces won't be an issue.
SSCCE
import java.io.BufferedReader;
import java.io.FileReader;
import java.util.ArrayList;
public class WordsInArray {
public static void main(String[] args) {
try{
BufferedReader buf = new BufferedReader(new FileReader("/home/little/Downloads/test"));
ArrayList<String> words = new ArrayList<>();
String lineJustFetched = null;
String[] wordsArray;
while(true){
lineJustFetched = buf.readLine();
if(lineJustFetched == null){
break;
}else{
wordsArray = lineJustFetched.split("\t");
for(String each : wordsArray){
if(!"".equals(each)){
words.add(each);
}
}
}
}
for(String each : words){
System.out.println(each);
}
buf.close();
}catch(Exception e){
e.printStackTrace();
}
}
}
Output
John
likes to play tennis
Sherlock
likes to solve crime
回答2:
If you separated Name and Hobby column with tab \t, you should do something like this (and don't forget to close scan at end):
public void readFile() throws FileNotFoundException{
Scanner scan = new Scanner(new File("D://a.txt"));
ArrayList<String> names = new ArrayList<String>();
ArrayList<String> hobbies = new ArrayList<String>();
while(scan.hasNext()){
String curLine = scan.nextLine();
String[] splitted = curLine.split("\t");
String name = splitted[0].trim();
String hobby = splitted[1].trim();
if(!"Name".equals(name)){
names.add(name);
}
if(!"Hobby".equals(hobby)){
hobbies.add(hobby);
}
}
System.out.println(names);
System.out.println(hobbies);
scan.close();
}
回答3:
For others still stumbling upon this.
Using Stream API (Java 8), this can be done as
This shows
- Filter method to filter the first header element from the list
- map method to map each element in stream to another element for new stream.
package com.bhavya.stackoverflow.examples.q19575308;
import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.Arrays;
import java.util.HashMap;
import java.util.function.Predicate;
/**
* Java 8 Stream API to handle file reading.
*
* @author bhavya.work
*/
public class StreamTests {
public static void main(String[] args) {
try {
InputStream fileInputStream;
BufferedReader bufferedReader;
final String filepathInSamePackage = "textfile.txt";
//filter predicate
Predicate<String> filterFirstLine =
line -> !(
"Name".equals(line.split("\t", -1)[0])
&& "Hobby".equals(line.split("\t", -1)[1])
);
//Implementation 1 returns Arrays as asked.
System.out.println("==ArrayList==");
fileInputStream = StreamTests.class.getResourceAsStream(filepathInSamePackage);
bufferedReader = new BufferedReader(new InputStreamReader(fileInputStream));
bufferedReader
.lines()
.filter(filterFirstLine)
.map(s -> {
String[] splitStrings = s.split("\t", -1);
return Arrays.asList(splitStrings);
}).forEach(System.out::println);
//Implementation 2 returns HashMap as another example
fileInputStream = StreamTests.class.getResourceAsStream(filepathInSamePackage);
bufferedReader = new BufferedReader(new InputStreamReader(fileInputStream));
System.out.println("\n==HashMap==");
bufferedReader
.lines()
.filter(filterFirstLine)
.map(s -> {
String[] splitStrings = s.split("\t", -1);
HashMap<String, String> stringStringMap = new HashMap<>();
stringStringMap.put(splitStrings[0], splitStrings[1]);
return stringStringMap;
}).forEach(System.out::println);
}
catch (Exception e) {
e.printStackTrace();
}
}
}
And the output
==ArrayList==
[Susy, eat fish]
[Anna, gardening]
[Billy, bowling with friends]
==HashMap==
{Susy=eat fish}
{Anna=gardening}
{Billy=bowling with friends}
回答4:
For future references when you parse out tab there is a delimiter such as "\t" for tab. Use that instead of .split(" ")
Also, when your error is thrown because it means no character is found, hence the -1, so when you try to store it in an Array... -1 is not valid. (throw in a check for that)
You can step throw your program F10 or F11..or some other key depending on your IDE
Just some tips
回答5:
You should try the commons-lang library. Among many other useful things you can split a string using a delimiter:
String x="Billy bowling with friends";
String y[]=StringUtils.split(x, '\t');
Assuming there is a tab between Billy and bowling,
- y[0] contains "Billy"
- y1 contains "bowling with friends"
来源：https://stackoverflow.com/questions/19575308/read-a-file-separated-by-tab-and-put-the-words-in-an-arraylist