strings - Pattern and Matcher

A simple example for use Pattern and Matcher 

// strings/TestRegularExpression.java
// (c)2017 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.
// Simple regular expression demonstration
// {java TestRegularExpression
// abcabcabcdefabc "abc+" "(abc)+" }

import java.util.regex.*;

public class TestRegularExpression {
  public static void main(String[] args) {
    // Pattern p1 = Pattern.compile("a*b");
    // Matcher m1 = p1.matcher("aaaaab");
    // boolean b = m1.matches();
    // System.out.println("b:" + b); // true

    if (args.length < 2) {
      System.out.println(
          "Usage:\njava TestRegularExpression " + "characterSequence regularExpression+");
      System.exit(0);
    }
    System.out.println("Input: \"" + args[0] + "\"");
    for (String arg : args) {
      System.out.println("Regular expression: \"" + arg + "\"");
      Pattern p = Pattern.compile(arg); // regular expression
      Matcher m = p.matcher(args[0]);
      while (m.find()) {
        System.out.println(
            "Match \"" + m.group() + "\" at positions " + m.start() + "-" + (m.end() - 1));
      }
    }
  }
}
/* Output:
Input: "abcabcabcdefabc"
Regular expression: "abcabcabcdefabc"
Match "abcabcabcdefabc" at positions 0-14
Regular expression: "abc+"
Match "abc" at positions 0-2
Match "abc" at positions 3-5
Match "abc" at positions 6-8
Match "abc" at positions 12-14
Regular expression: "(abc)+"
Match "abcabcabc" at positions 0-8
Match "abc" at positions 12-14
*/

matcher

public Matcher matcher(CharSequence input)

Creates a matcher that will match the given input against this pattern.

Parameters:

input - The character sequence to be matched

Returns:

A new matcher for this pattern

 

group

public String group()

Returns the input subsequence matched by the previous match.

For a matcher m with input sequence s, the expressions m.group() and s.substring(m.start(), m.end()) are equivalent.

Note that some patterns, for example a*, match the empty string. This method will return the empty string when the pattern successfully matches the empty string in the input.

Specified by:

group in interface MatchResult

Returns:

The (possibly empty) subsequence matched by the previous match, in string form

Throws:

IllegalStateException - If no match has yet been attempted, or if the previous match operation failed

 

note the bash command

java TestRegularExpression abcabcabcdefabc "(abc)+" 

if we don't add "" in above sentence, it would prompt:

bash: syntax error near unexpected token `('

java TestRegularExpression abcabcabcdefabc "abc+"  == java TestRegularExpression abcabcabcdefabc  abc

 

references:

1. On Java 8 - Bruce Eckel

2. https://github.com/wangbingfeng/OnJava8-Examples/blob/master/strings/TestRegularExpression.java

3. https://docs.oracle.com/javase/8/docs/api/java/util/regex/Pattern.html#matcher-java.lang.CharSequence-

4. https://docs.oracle.com/javase/8/docs/api/java/util/regex/Matcher.html#group--