How to match start or end of given string using regex in java

Question

I want to match a string which starts or ends with a "test" using regex in java.

Match Start of the string:- String a = "testsample";

  String pattern = "^test";

  // Create a Pattern object
  Pattern r = Pattern.compile(pattern);

  // Now create matcher object.
  Matcher m = r.matcher(a);

Match End of the string:- String a = "sampletest";

  String pattern = "test$";

  // Create a Pattern object
  Pattern r = Pattern.compile(pattern);

  // Now create matcher object.
  Matcher m = r.matcher(a);

How can I combine regex for starts or ends with a given string ?

Avinash Raj · Accepted Answer · 2016-01-22 05:25:29Z

18

Just use regex alternation operator |.

String pattern = "^test|test$";

In matches method, it would be,

string.matches("test.*|.*test");

answered Jan 22, 2016 at 5:25

Avinash Raj

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1 Comment

Galet Over a year ago

Is there a way to use "test" string at once in regex or inside matches method

Ajmal Muhammad · Accepted Answer · 2016-01-22 05:38:42Z

3

use this code

String string = "test";
String pattern = "^" + string+"|"+string+"$";

// Create a Pattern object
Pattern r = Pattern.compile(pattern);

// Now create matcher object.
Matcher m = r.matcher(a);

answered Jan 22, 2016 at 5:38

Ajmal Muhammad

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2 Comments

Jason Over a year ago

This is the same solution as @AvinashRaj

Jason Over a year ago

I did, and you are proposing the same regex.

Wiktor Stribiżew · Accepted Answer · 2016-01-22 08:05:11Z

Here is how you can build a dynamic regex that you can use both with Matcher#find() and Matcher#matches():

String a = "testsample";
String word = "test";
String pattern = "(?s)^(" + Pattern.quote(word) + ".*$|.*" + Pattern.quote(word) + ")$";
// Create a Pattern object
Pattern r = Pattern.compile(pattern);
// Now create matcher object.
Matcher m = r.matcher(a);
if (m.find()){
    System.out.println("true - found with Matcher"); 
} 
// Now, the same pattern with String#matches:
System.out.println(a.matches(pattern));

See IDEONE demo

The pattern will look like ^(\Qtest\E.*$|.*\Qtest\E)$ (see demo) since the word is searched for as a sequence of literal characters (this is achieved with Pattern.quote). The ^ and $ that are not necessary for matches are necessary for find (and they do not prevent matches from matching, either, thus, do not do any harm).

Also, note the (?s) DOTALL inline modifier that makes a . match any character including a newline.

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