BAEL-4163 - Counting matches for a regex (#9466)

* BAEL-4163 - Counting matches for a regex

* BAEL-4163 - Fixing build problemns

* BAEL-4163 : Adding more test to assure quality of the examples

* BAEL-4163 : Fixing request changes

* BAEL-4163 : Minor adjustements to give more context about the commented out tests

* BAEL-4163 : Tests for overlap example

core-java-modules/core-java-regex/src/test/java/com/baeldung/regex/countmatches/CountMatchesUnitTest.java

@@ -0,0 +1,110 @@
+package com.baeldung.regex.countmatches;
+
+import static org.junit.Assert.assertNotEquals;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+import org.junit.Test;
+
+/**
+ * Unit Test intended to count number of matches of a RegEx using Java 8 and 9.
+ * 
+ * Java 9 is needed to run the commented out tests.
+ */
+public class CountMatchesUnitTest {
+
+    private static final Pattern EMAIL_ADDRESS_PATTERN = Pattern.compile("([a-z0-9_.-]+)@([a-z0-9_.-]+[a-z])");
+    private static final String TEXT_CONTAINING_EMAIL_ADDRESSES = "You can contact me through: writer@baeldung.com, editor@baeldung.com and team@bealdung.com";
+    private static final String TEXT_CONTAINING_FIVE_EMAIL_ADDRESSES = "Valid emails are: me@gmail.com, you@baeldung.com, contact@hotmail.com, press@anysite.com and support@bealdung.com";
+    private static final String TEXT_CONTAINING_OVERLAP_EMAIL_ADDRESSES = "Try to contact us at team@baeldung.comeditor@baeldung.com, support@baeldung.com.";
+
+    @Test
+    public void givenContainingEmailString_whenJava8Match_thenCountMacthesFound() {
+        Matcher countEmailMatcher = EMAIL_ADDRESS_PATTERN.matcher(TEXT_CONTAINING_EMAIL_ADDRESSES);
+
+        int count = 0;
+        while (countEmailMatcher.find()) {
+            count++;
+        }
+
+        assertEquals(3, count);
+    }
+
+    @Test
+    public void givenContainingFiveEmailsString_whenJava8Match_thenCountMacthesFound() {
+        Matcher countFiveEmailsMatcher = EMAIL_ADDRESS_PATTERN.matcher(TEXT_CONTAINING_FIVE_EMAIL_ADDRESSES);
+
+        int count = 0;
+        while (countFiveEmailsMatcher.find()) {
+            count++;
+        }
+
+        assertEquals(5, count);
+    }
+
+    @Test
+    public void givenStringWithoutEmails_whenJava8Match_thenCountMacthesNotFound() {
+        Matcher noEmailMatcher = EMAIL_ADDRESS_PATTERN.matcher("Simple text without emails.");
+
+        int count = 0;
+        while (noEmailMatcher.find()) {
+            count++;
+        }
+
+        assertEquals(0, count);
+    }
+
+    @Test
+    public void givenStringWithOverlappingEmails_whenJava8Match_thenCountWrongMatches() {
+        Matcher countOverlappingEmailsMatcher = EMAIL_ADDRESS_PATTERN.matcher(TEXT_CONTAINING_OVERLAP_EMAIL_ADDRESSES);
+
+        int count = 0;
+        while (countOverlappingEmailsMatcher.find()) {
+            count++;
+        }
+
+        assertNotEquals(3, count);
+    }
+
+    @Test
+    public void givenContainingEmailString_whenStartingInJava9Match_thenCountMacthesFound() {
+        // uncomment to try with Java 9
+        // Matcher countEmailMatcher = EMAIL_ADDRESS_PATTERN.matcher(TEXT_CONTAINING_EMAIL_ADDRESSES);
+
+        // long count = countEmailMatcher.results().count();
+
+        // assertEquals(3, count);
+    }
+
+    @Test
+    public void givenContainingFiveEmailsString_whenStartingInJava9Match_thenCountMacthesFound() {
+        // uncomment to try with Java 9
+        // Matcher countFiveEmailsMatcher = EMAIL_ADDRESS_PATTERN.matcher(TEXT_CONTAINING_FIVE_EMAIL_ADDRESSES);
+
+        // long count = countFiveEmailsMatcher.results().count();
+
+        // assertEquals(5, count);
+    }
+
+    @Test
+    public void givenStringWithoutEmails_whenJava9Match_thenCountMacthesNotFound() {
+        // uncomment to try with Java 9
+        // Matcher noEmailMatcher = EMAIL_ADDRESS_PATTERN.matcher("Simple text without emails.");
+
+        // long count = noEmailMatcher.results().count();
+
+        // assertEquals(0, count);
+    }
+
+    @Test
+    public void givenStringWithOverlappingEmails_whenJava9Match_thenCountWrongMatches() {
+        // uncomment to try with Java 9
+        // Matcher countOverlappingEmailsMatcher = EMAIL_ADDRESS_PATTERN.matcher(TEXT_CONTAINING_OVERLAP_EMAIL_ADDRESSES);
+
+        // long count = countOverlappingEmailsMatcher.results().count();
+
+        // assertNotEquals(3, count);
+    }
+}