[BAEL-829] Number of occurrences of a char in a String (#1785)

* injecting beans

* XML-based configuration replaced with Java Config.

* [BAEL-431] Exploring TestRestTemplate.

* Revert of evaluation task "XML-based configuration replaced with Java Config."

This reverts commit 66471cf0574c85f8ff514ec4caf5ba44ebba1a74.

* Revert of evaluation task "injecting beans"

This reverts commit d2ac20185e636245bc0ae0b4ccb952965de88e28.

* [BAEL-431] fix to the tests in TestRestTemplateBasicLiveTest.

* [BAEL-431] added more meaningful user and password for auth.

* [BAEL-820] examples of wait() and sleep() methods.

* [BAEL-820] wait() and sleep() examples.

* [BAEL-829] number of occurences of a char in a String.

* [BAEL-829] printlns changed to assertions.

* [BAEL-829] improved names of the tests.

core-java/src/test/java/com/baeldung/java/countingChars/CountCharsExample.java

@@ -0,0 +1,93 @@
+package com.baeldung.java.countingChars;
+
+import com.google.common.base.CharMatcher;
+import org.apache.commons.lang.StringUtils;
+import org.junit.Test;
+
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+import static org.junit.Assert.assertEquals;
+
+
+/***
+ * Example of counting chars in a String.
+ */
+public class CountCharsExample {
+
+    @Test
+    public void givenString_whenUsingLoop_thenCountChars() {
+        String someString = "elephant";
+        char someChar = 'e';
+        int count = 0;
+        for (int i = 0; i < someString.length(); i++) {
+            if (someString.charAt(i) == someChar) {
+                count++;
+            }
+        }
+        assertEquals(2, count);
+    }
+
+    @Test
+    public void givenString_whenUsingReplace_thenCountChars() {
+        String someString = "elephant";
+        int count = someString.length() - someString.replace("e", "").length();
+        assertEquals(2, count);
+    }
+
+    @Test
+    public void givenString_whenUsingSplit_thenCountChars() {
+        String someString = "elephant";
+        int count = someString.split("e", -1).length - 1;
+        assertEquals(2, count);
+    }
+
+    @Test
+    public void givenString_whenUsingReqExp_thenCountChars() {
+        Pattern pattern = Pattern.compile("[^e]*e");
+        Matcher matcher = pattern.matcher("elephant");
+        int count = 0;
+        while (matcher.find()) {
+            count++;
+        }
+        assertEquals(2, count);
+    }
+
+    @Test
+    public void givenString_whenUsingRecursion_thenCountChars() {
+        int count = useRecursion("elephant", 'e', 0);
+        assertEquals(2, count);
+    }
+
+    private int useRecursion(String someString, char searchedChar, int index) {
+        if (index >= someString.length()) {
+            return 0;
+        }
+
+        int count = someString.charAt(index) == searchedChar ? 1 : 0;
+        return count + useRecursion(someString, searchedChar, index + 1);
+    }
+
+    @Test
+    public void givenString_whenUsingStringUtils_thenCountChars() throws InterruptedException {
+        int count = StringUtils.countMatches("elephant", "e");
+        assertEquals(2, count);
+    }
+
+    @Test
+    public void givenString_whenUsingJava8Features_thenCountChars() {
+        String someString = "elephant";
+        long count = someString.chars().filter(ch -> ch == 'e').count();
+        assertEquals(2, count);
+
+        long count2 = someString.codePoints().filter(ch -> ch == 'e').count();
+        assertEquals(2, count2);
+    }
+
+    @Test
+    public void givenString_whenUsingGuavaCharMatcher_thenCountChars() {
+        int count = CharMatcher.is('e').countIn("elephant");
+        assertEquals(2, count);
+    }
+
+}