BAEL-6195 Find the First Embedded Occurrence of an Integer in a Java String (#13448)

* initialize arraylist with null or zeros

* configure pom parent

* move code

* delete module

* BAEL-6195

* first occurence of an integer

* review changes

core-java-modules/core-java-string-algorithms-3/src/main/java/com/baeldung/firstocurrenceofaninteger/FirstOccurrenceOfAnInteger.java

@@ -0,0 +1,18 @@
+package com.baeldung.firstocurrenceofaninteger;
+
+public class FirstOccurrenceOfAnInteger {
+
+    static Integer findFirstInteger(String s) {
+        int i = 0;
+        while (i < s.length() && !Character.isDigit(s.charAt(i))) {
+            i++;
+        }
+        int j = i;
+        while (j < s.length() && Character.isDigit(s.charAt(j))) {
+            j++;
+        }
+        return Integer.parseInt(s.substring(i, j));
+    }
+
+}
+

core-java-modules/core-java-string-algorithms-3/src/test/java/com/baeldung/firstocurrenceofaninteger/FirstOccurrenceOfAnIntegerUnitTest.java

@@ -0,0 +1,46 @@
+package com.baeldung.firstocurrenceofaninteger;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.Scanner;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+import java.util.stream.Collectors;
+
+class FirstOccurrenceOfAnIntegerUnitTest {
+
+    @Test
+    void whenUsingPatternMatcher_findFirstInteger() {
+        String s = "ba31dung123";
+        Matcher matcher = Pattern.compile("\\d+").matcher(s);
+        matcher.find();
+        int i = Integer.parseInt(matcher.group());
+        Assertions.assertEquals(31, i);
+    }
+
+    @Test
+    void whenUsingScanner_findFirstInteger() {
+        int i = new Scanner("ba31dung123").useDelimiter("\\D+").nextInt();
+        Assertions.assertEquals(31, i);
+    }
+
+    @Test
+    void whenUsingSplit_findFirstInteger() {
+        String str = "ba31dung123";
+        List<String> tokens = Arrays.stream(str.split("\\D+"))
+                .filter(s -> s.length() > 0).collect(Collectors.toList());
+        Assertions.assertEquals(31, Integer.parseInt(tokens.get(0)));
+    }
+
+    @Test
+    void whenUsingCustomMethod_findFirstInteger() {
+        String str = "ba31dung123";
+        Integer i = FirstOccurrenceOfAnInteger.findFirstInteger(str);
+        Assertions.assertEquals(31, i);
+    }
+
+
+}