Understanding java-11.4 Regular Expressions from the beginning (3)-pattern and Matcher

In this chapter we will discuss the pattern and matcher.

Before we were all simply using regular expressions to match strings, in fact Java provides a strong regular matching class, we will follow a few examples to illustrate.

Package Com.ray.ch11;import Java.util.regex.matcher;import Java.util.regex.pattern;public class Test {public static void Main (string[] args) {String teststr = "abc"; String[] regulars = {"A", "abc", "//d", "A?"}; SYSTEM.OUT.PRINTLN ("Input:" + teststr); for (String item:regulars) {Pattern pattern = pattern.compile (item); Matcher Matcher = Pattern.matcher (TESTSTR), while (Matcher.find ()) {System.out.println ("Regular:" + Item + "Start:" + MATC Her.start () + "End:" + matcher.end ());}}}

Output:

Input:abc
Regular:a start:0 end:1
REGULAR:ABC start:0 End:3
Regular:a? start:0 end:1
Regular:a? Start:1 end:1
Regular:a? Start:2 End:2
Regular:a? Start:3 End:3

As you can see from the above output, we can not only get the result of the match, but also through Matcher, we can get a lot of other information, such as where the above match in that position, in which place to end.

Let's change the input below and then change the rules to see another example:

Package Com.ray.ch11;import Java.util.regex.matcher;import Java.util.regex.pattern;public class Test {public static void Main (string[] args) {String teststr = "Java now has regular expression"; String[] regulars = {"^java", "\\breg.*", "N.w\\s+h (a|i) S", "s?", "S+", "s*", "s{4}", "S{1}", "s{1,3}"}; SYSTEM.OUT.PRINTLN ("Input:" + teststr); for (String item:regulars) {Pattern pattern = pattern.compile (item); Matcher Matcher = Pattern.matcher (TESTSTR), while (Matcher.find ()) {System.out.println ("Regular:" + Item + "Start:" + MATC Her.start () + "End:" + matcher.end ());}}}

Output:

Input:java now have regular expression
Regular:^java start:0 End:4
Regular:n.w\s+h (a|i) s start:5 end:12
Regular:s? start:0 end:0
Regular:s? Start:1 end:1
Regular:s? Start:2 End:2
Regular:s? Start:3 End:3
Regular:s? Start:4 End:4
Regular:s? Start:5 End:5
Regular:s? Start:6 End:6
Regular:s? Start:7 End:7
Regular:s? Start:8 End:8
Regular:s? Start:9 End:9
Regular:s? Start:10 end:10
Regular:s? Start:11 End:12
Regular:s? Start:12 End:12
Regular:s? Start:13 end:13
Regular:s? Start:14 end:14
Regular:s? Start:15 end:15
Regular:s? Start:16 end:16
Regular:s? Start:17 end:17
Regular:s? Start:18 end:18
Regular:s? Start:19 end:19
Regular:s? Start:20 end:20
Regular:s? Start:21 end:21
Regular:s? Start:22 end:22
Regular:s? Start:23 end:23
Regular:s? Start:24 end:24
Regular:s? Start:25 end:25
Regular:s? Start:26 end:27
Regular:s? Start:27 end:28
Regular:s? Start:28 end:28
Regular:s? Start:29 end:29
Regular:s? Start:30 end:30
Regular:s? Start:31 end:31
regular:s+ start:11 End:12
regular:s+ start:26 end:28
regular:s* start:0 end:0
regular:s* start:1 end:1
regular:s* Start:2 End:2
regular:s* Start:3 End:3
regular:s* Start:4 End:4
regular:s* Start:5 End:5
regular:s* Start:6 End:6
regular:s* Start:7 End:7
regular:s* Start:8 End:8
regular:s* Start:9 End:9
regular:s* start:10 End:10
regular:s* start:11 End:12
regular:s* Start:12 End:12
regular:s* start:13 end:13
regular:s* start:14 end:14
regular:s* start:15 end:15
regular:s* start:16 end:16
regular:s* start:17 end:17
regular:s* start:18 end:18
regular:s* start:19 end:19
regular:s* start:20 end:20
regular:s* start:21 end:21
regular:s* start:22 end:22
regular:s* start:23 end:23
regular:s* start:24 end:24
regular:s* start:25 end:25
regular:s* start:26 end:28
regular:s* start:28 end:28
regular:s* start:29 end:29
regular:s* start:30 end:30
regular:s* start:31 end:31
Regular:s{1} start:11 End:12
Regular:s{1} start:26 end:27
Regular:s{1} start:27 end:28
regular:s{1,3} start:11 End:12
regular:s{1,3} start:26 end:28

Explain:

(1) The Find () function above is like an iterator that iterates through every character in a string. and find (int) can also place parameters, to decide to start the iteration from the first few positions.

(2) The above start () and end () returns the position of the beginning and end of the match

In addition to the above features, we can also add parameters to the pattern to qualify the match.

Package Com.ray.ch11;import Java.util.regex.matcher;import Java.util.regex.pattern;public class Test {public static void Main (string[] args) {String teststr = "Java now have regular expression\n" + "Java now have regular expression"; String[] regulars = {"^java"}; SYSTEM.OUT.PRINTLN ("Input:" + teststr); for (String item:regulars) {Pattern pattern = pattern.compile (item, Pattern.case _insensitive| Pattern.multiline); Matcher Matcher = Pattern.matcher (TESTSTR), while (Matcher.find ()) {System.out.println ("Regular:" + Item + "Start:" + MATC Her.start () + "End:" + matcher.end () + "group:" + Matcher.group ());}}}

Output:

Input:java now have regular expression
JAVA now have regular expression
Regular:^java start:0 End:4 Group:java
Regular:^java start:32 end:36 Group:java

Summary: This chapter mainly describes the pattern and matcher.

This chapter is here, thank you.

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Understanding java-11.4 Regular Expressions from the beginning (3)-pattern and Matcher