Case-insensitive string matching in Java without anchors

Question

NOTE: This is NOT a question about case-insensitive matching. It is a question about regex anchors.

I'm having a lot of trouble doing basic case insensitive matching in Java:

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class match {
    public static void main(String[] args) {
        String prompt="das101.lo1>";
        String str="automate@DAS101.LO1>";

        Pattern ignore = Pattern.compile(prompt.toUpperCase(), Pattern.CASE_INSENSITIVE);
        Matcher mIgn  = ignore.matcher(str);
        if(mIgn.matches())
            System.out.println(str+" Matches " + prompt.toUpperCase());
        else
            System.out.println(str+" Doesn't Match " + prompt.toUpperCase());

        char[] cStr = str.toCharArray();
        char[] cPrompt = prompt.toUpperCase().toCharArray();

        /* Verify that strings match */
        for(int i=cPrompt.length-1, j=cStr.length-1; i>=0 && j>=0 ; --i,--j) {
            if (cPrompt[i]==cStr[j])
                System.out.println("Same: "+ cPrompt[i]+":" + cStr[j]);
            else
                System.out.println("Different: "+ cPrompt[i]+":" + cStr[j]);
        }
    }
}

The output:

samveen@javadev-tahr:/tmp$ javac match.java
samveen@javadev-tahr:/tmp$ java match
automate@DAS101.LO1> Doesn't Match DAS101.LO1>
Same: >:>
Same: 1:1
Same: O:O
Same: L:L
Same: .:.
Same: 1:1
Same: 0:0
Same: 1:1
Same: S:S
Same: A:A
Same: D:D

If I change if(mIgn.matches()) to if(mIgn.find()), I get this simple string pattern match working:

samveen@javadev-tahr:/tmp$ javac match.java
samveen@javadev-tahr:/tmp$ java match
automate@DAS101.LO1> Matches DAS101.LO1>
Same: >:>
Same: 1:1
Same: O:O
Same: L:L
Same: .:.
Same: 1:1
Same: 0:0
Same: 1:1
Same: S:S
Same: A:A
Same: D:D

Where am I going wrong?

I referred to Case-Insensitive Matching in Java RegEx and Methods of the Pattern Class

score 6 · Accepted Answer · answered Oct 16 '14 at 14:41

String.matches requires the entire string to match the pattern. As if the pattern has an implied "^...$".

Pattern ignore = Pattern.compile(".*" + Pattern.quote(prompt) + ".*",
    Pattern.CASE_INSENSITIVE);

is for a find like match.

This could have been done with the original pattern as:

if (mIgn.find()) {
    System.out.println("Found at position " + mIgn.start());
}

score 2 · Answer 2 · edited May 23 '17 at 12:00

2

Matches return true if the whole string matches the given pattern. For this it prefix ur matcher with '^' and suffix with '$' sign and hence it is not going to look for a substring.

find() return true in case of substring matches also.

Have a look - Difference between matches() and find() in Java Regex

edited May 23 '17 at 12:00

Community

1
1

answered Oct 16 '14 at 15:02

kunsingh

254
2
7

score 1 · Answer 3 · answered Oct 16 '14 at 14:40

matches() only returns true if the whole input matches the pattern, not if part of the input matches the pattern.

The input automate@DAS101.LO1> does not match the complete pattern das101.lo1>.

That explains the different result you get when you use find() instead of matches().

score 1 · Answer 4 · answered Feb 26 '18 at 17:30

1

Use ?i regex with .matches for case insensitive matching:

    // ?i = case insensitive match
    if (mIgn.matches("(?i:str)")) {
        ......
    } else {
        ......
    }

answered Feb 26 '18 at 17:30

Stuart Cardall

2,099
24
18

On reading the question in detail, you will see that the problem was not about the case insensitive matching as much as about matching the beginning and end of string anchors. However, thank you for pointing out that the question title is misleading, even if indirectly. I will correct the title. – Samveen Apr 19 '18 at 05:18

score 0 · Answer 5 · answered Oct 10 '18 at 11:19

0

Use this Utility method for case-insensitive matches

 // utlity method for mathcesIgonerCase
 public static boolean mathcesIgonerCase(String string1, String sentence){
     return string1.matches("(?i:.*"+sentence+".*)");
 }

answered Oct 10 '18 at 11:19

MADHAIYAN M

2,028
25
22

Case-insensitive string matching in Java without anchors

5 Answers5