convert a String[] to Arraylist<String> with java

Question

I want to convert a string that I get from a file, to an arraylist. I tried it this way, but it doesn't work:

import java.io.*; import java.util.*; public class Data { static File file = DataSaver.file; static List<String> data = new ArrayList<String>(512); public static void a() throws Exception { FileInputStream fis = new FileInputStream(file); DataInputStream dis = new DataInputStream(fis); BufferedReader reader = new BufferedReader(new InputStreamReader(dis)); if(!file.exists()) { throw new IOException("Datafile not found."); } else { String[] string = reader.readLine().split("$"); for(int i = 0; i < string.length; i++) { data.add(string[i]); } } dis.close(); System.out.println(data.toString()); //for debugging purposes. } }

Ouput: [$testdata1$testdata2$]

Wanted output: [testdata1, testdata2]

File content: $testdata1$testdata2$

Can someone help me?

It's a bad variable name. Java may allow it because it's not case-sensitive with it's classes, but that wouldn't work in C# (where string is an alias for String). Furthermore, it doesn't really describe what's contained in the variable. — David B
– David B, Commented Jul 23, 2012 at 18:26
Please don't use DataInputStream if you want to read text, its more confusing than useful. — Peter Lawrey
– Peter Lawrey, Commented Aug 15, 2012 at 11:33

dacwe · Accepted Answer · 2012-07-23 18:17:45Z

String.split takes a regex and $ is a special char that need to be escaped. Also, the first char is a $ so splitting would end up with an empty first element (you need to remove it somehow, this is one way:

String[] string = reader.readLine().substring(1).split("\\$");

...or:

String[] string = reader.readLine().split("\\$"); for (int i = 0; i < string.length; i++) if (!string[i].isEmpty()) data.add(string[i]);

Kumar Vivek Mitra · Accepted Answer · 2012-07-23 18:32:31Z

1. Use ("\\$") to remove the special meaning of "$".

2. Use Arrays.asList() for the Conversion of Array TO ArrayList

From Java Docs :

Returns a fixed-size list backed by the specified array. (Changes to the returned list "write through" to the array.) This method acts as bridge between array-based and collection-based APIs, in combination with Collection.toArray(). The returned list is serializable and implements RandomAccess.

This method also provides a convenient way to create a fixed-size list initialized to contain several elements:

eg:

String[] string = reader.readLine().split("\\$"); ArrayList<String> arr = new ArrayList<String>(Arrays.asList(string));

@dacwe Isnt the List from Arrays.asList() directly backed by the array? Which would mean almost no overhead.

kosa · Accepted Answer · 2012-07-23 18:18:08Z

You need to escape special characters with \\.

Change your split statement like below

String[] string = reader.readLine().split("\\$");

amicngh · Accepted Answer · 2012-07-23 18:21:15Z

0

Adding to @dacwe

String[] string = reader.readLine().substring(1).split("\\$"); List<String> data =Arrays.asList(string);

answered Jul 23, 2012 at 18:21

amicngh

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2 Comments

David B Over a year ago

If you want to contribute to his answer, edit it or leave a comment.

dacwe Over a year ago

Alright, but @user1546467 wanted an ArrayList (asList returns a list backed by the array).

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