Regex - recognize the indefinite article “a” or “an” using JAVA
-
29-10-2019 - |
Question
my task is to devise a regular expression that will recognize the indefinite article in English – the word “a” or “an” i.e. to write a regular expression to identify the word a or the word an. I must test the expression by writing a test driver which reads a file containing approximately ten lines of text. Your program should count the occurrences of the words “a” and “an”.I shall not match the characters a and an in words such as than.
This is my code so far:
import java.io.IOException;
import java.util.Arrays;
import java.util.regex.Pattern;
import java.util.regex.Matcher;
public class RegexeFindText {
public static void main(String[] args) throws IOException {
// Input for matching the regexe pattern
String file_name = "Testing.txt";
ReadFile file = new ReadFile(file_name);
String[] aryLines = file.OpenFile();
String asString = Arrays.toString(aryLines);
// Regexe to be matched
String regexe = ""; //<<--this is where the problem lies
int i;
for ( i=0; i < aryLines.length; i++ ) {
System.out.println( aryLines[ i ] ) ;
}
// Step 1: Allocate a Pattern object to compile a regexe
Pattern pattern = Pattern.compile(regexe);
//Pattern pattern = Pattern.compile(regexe, Pattern.CASE_INSENSITIVE);
// case- insensitive matching
// Step 2: Allocate a Matcher object from the compiled regexe pattern,
// and provide the input to the Matcher
Matcher matcher = pattern.matcher(asString);
// Step 3: Perform the matching and process the matching result
// Use method find()
while (matcher.find()) { // find the next match
System.out.println("find() found the pattern \"" + matcher.group()
+ "\" starting at index " + matcher.start()
+ " and ending at index " + matcher.end());
}
// Use method matches()
if (matcher.matches()) {
System.out.println("matches() found the pattern \"" + matcher.group()
+ "\" starting at index " + matcher.start()
+ " and ending at index " + matcher.end());
} else {
System.out.println("matches() found nothing");
}
// Use method lookingAt()
if (matcher.lookingAt()) {
System.out.println("lookingAt() found the pattern \"" + matcher.group()
+ "\" starting at index " + matcher.start()
+ " and ending at index " + matcher.end());
} else {
System.out.println("lookingAt() found nothing");
}
}
}
My question is simply what do I have to use to find those words within my text? Any help would be much appreciated, thanks!
Solution
Here's the regex that will match "a" or "an":
String regex = "\\ban?\\b";
Let's break that regex down:
\b
means word boundary (a single back slash is written as"\\"
in java)a
is simply a literal"a"
n?
means zero or one literal"n"
Licensed under: CC-BY-SA with attribution
Not affiliated with StackOverflow