strings - Macher - start() and end() and related methods

start

public int start()

Returns the start index of the previous match.

Specified by:

start in interface MatchResult

Returns:

The index of the first character matched

Throws:

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

end

public int end()

Returns the offset after the last character matched.

Return the index of the last character matched, plus one.

Specified by:

end in interface MatchResult

Returns:

The offset after the last character matched

Throws:

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

find

public boolean find()

Attempts to find the next subsequence of the input sequence that matches the pattern.

This method will locate the regular expression anywhere in the input.

This method starts at the beginning of this matcher's region, or, if a previous invocation of the method was successful and the matcher has not since been reset, at the first character not matched by the previous match.

If the match succeeds then more information can be obtained via the start, end, and group methods.

Returns:

true if, and only if, a subsequence of the input sequence matches this matcher's pattern

for example:

// strings/StartEnd.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.

import java.util.regex.*;

public class StartEnd {
  public static String input =
      "As long as there is injustice, whenever a\n"
          + "Targathian baby cries out, wherever a distress\n"
          + "signal sounds among the stars "
          + "... We'll be there.\n"
          + "This fine ship, and this fine crew ...\n"
          + "Never give up! Never surrender!";

  private static class Display {
    private boolean regexPrinted = false;
    private String regex;

    Display(String regex) {
      this.regex = regex;
    }

    void display(String message) {
      if (!regexPrinted) {
        System.out.println(regex);
        regexPrinted = true;
      }
      System.out.println(message);
    }
  }

  static void examine(String s, String regex) {
    Display d = new Display(regex);
    Pattern p = Pattern.compile(regex);
    Matcher m = p.matcher(s);
    while (m.find()) {
      d.display("find() '" + m.group() + "' start = " + m.start() + " end = " + m.end());
    }
    if (m.lookingAt()) { // No reset() necessary
      d.display("lookingAt() start = " + m.start() + " end = " + m.end());
    }
    if (m.matches()) { // No reset() necessary
      d.display("matches() start = " + m.start() + " end = " + m.end());
    }
  }

  public static void main(String[] args) {
    for (String in : input.split("\n")) {
      System.out.println("input : " + in);
      for (String regex : new String[] {"\\w*ere\\w*", "\\w*ever", "T\\w+", "Never.*?!"}) {
        examine(in, regex);
      }
    }
  }
}
/* Output:
input : As long as there is injustice, whenever a
\w*ere\w*
find() 'there' start = 11 end = 16
\w*ever
find() 'whenever' start = 31 end = 39
input : Targathian baby cries out, wherever a distress
\w*ere\w*
find() 'wherever' start = 27 end = 35
\w*ever
find() 'wherever' start = 27 end = 35
T\w+
find() 'Targathian' start = 0 end = 10
lookingAt() start = 0 end = 10
input : signal sounds among the stars ... We'll be there.

\w*ere\w*
find() 'there' start = 43 end = 48
input : This fine ship, and this fine crew ...
T\w+
find() 'This' start = 0 end = 4
lookingAt() start = 0 end = 4
input : Never give up! Never surrender!
\w*ever
find() 'Never' start = 0 end = 5
find() 'Never' start = 15 end = 20
lookingAt() start = 0 end = 5
Never.*?!
find() 'Never give up!' start = 0 end = 14
find() 'Never surrender!' start = 15 end = 31
lookingAt() start = 0 end = 14
matches() start = 0 end = 31
*/

lookingAt

public boolean lookingAt()

Attempts to match the input sequence, starting at the beginning of the region, against the pattern.

Like the matches method, this method always starts at the beginning of the region; unlike that method, it does not require that the entire region be matched.

If the match succeeds then more information can be obtained via the start, end, and group methods.

Returns:

true if, and only if, a prefix of the input sequence matches this matcher's 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

references:

1. On Java 8 - Bruce Eckel

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

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

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