AVAJAVA Web Tutorials

In another tutorial, we saw how we could get a List of the lines of a File very easily using the readLines() method of the FilesUtils class of the ApacheSW Commons IOS library. We can very easily alphabetize the List of lines with a call to Collections.sort(), since a List is a Collection. The ReadListOfLinesFromFileAndAlphabetize class demonstrates this.

ReadListOfLinesFromFileAndAlphabetize.java

package test;

import java.io.File;
import java.io.IOException;
import java.util.Collections;
import java.util.List;

import org.apache.commons.io.FileUtils;

public class ReadListOfLinesFromFileAndAlphabetize {

	public static void main(String[] args) {
		try {
			File file = new File("test.txt");
			List<String> lines = FileUtils.readLines(file);

			Collections.sort(lines);

			for (String line : lines) {
				System.out.println("line:" + line);
			}

		} catch (IOException e) {
			e.printStackTrace();
		}
	}
}

The test.txt file is shown here:

test.txt

this is
a test
of commons io

Executing ReadListOfLinesFromFileAndAlphabetize with test.txt generates the following console output:

line:a test
line:of commons io
line:this is

Note that Collections.sort() will treat uppercase and lowercase characters as not being equal when it performs a sort. To ignore case (and treat uppercase/lowercase the same), you can create a Comparator for strings and call toLowerCase() or toUppercase() when you compare them to 'equalize' the cases.