BAEL-3655: Article Find vs Matches in Java Regex API - done

core-java-modules/core-java-text/src/test/java/com/baeldung/regex/matcher/RegexMatcherFindVsMatchesTest.java

@@ -0,0 +1,63 @@
+package com.baeldung.regex.matcher;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+import org.junit.jupiter.api.Test;
+
+public class RegexMatcherFindVsMatchesTest {
+
+    @Test
+    public void whenFindFourDigitWorks_thenCorrect() {
+        Pattern stringPattern = Pattern.compile("\\d\\d\\d\\d");
+        Matcher m = stringPattern.matcher("goodbye 2019 and welcome 2020");
+
+        assertTrue(m.find());
+        assertEquals(8, m.start());
+        assertEquals("2019", m.group());
+        assertEquals(12, m.end());
+
+        assertTrue(m.find());
+        assertEquals(25, m.start());
+        assertEquals("2020", m.group());
+        assertEquals(29, m.end());
+
+        assertFalse(m.find());
+    }
+
+    @Test
+    public void givenStartIndex_whenFindFourDigitWorks_thenCorrect() {
+        Pattern stringPattern = Pattern.compile("\\d\\d\\d\\d");
+        Matcher m = stringPattern.matcher("goodbye 2019 and welcome 2020");
+
+        assertTrue(m.find(20));
+        assertEquals(25, m.start());
+        assertEquals("2020", m.group());
+        assertEquals(29, m.end());
+    }
+
+    @Test
+    public void whenMatchFourDigitWorks_thenFail() {
+        Pattern stringPattern = Pattern.compile("\\d\\d\\d\\d");
+        Matcher m = stringPattern.matcher("goodbye 2019 and welcome 2020");
+        assertFalse(m.matches());
+    }
+
+    @Test
+    public void whenMatchFourDigitWorks_thenCorrect() {
+        Pattern stringPattern = Pattern.compile("\\d\\d\\d\\d");
+        Matcher m = stringPattern.matcher("2019");
+
+        assertTrue(m.matches());
+        assertEquals(0, m.start());
+        assertEquals("2019", m.group());
+        assertEquals(4, m.end());
+
+        assertTrue(m.matches());// matches will always return the same return
+    }
+
+}