BAEL-6195

core-java-modules/core-java-regex-2/src/main/java/com/baeldung/firstoccurrenceofaninteger/FirstOccurrenceOfAnInteger.java

@@ -0,0 +1,16 @@
+package com.baeldung.firstoccurrenceofaninteger;
+
+public class FirstOccurrenceOfAnInteger {
+
+	public 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-regex-2/src/test/java/com/baeldung/firstoccurrenceofaninteger/FirstOccurrenceOfAnIntegerTests.java

@@ -0,0 +1,47 @@
+package com.baeldung.firstoccurrenceofaninteger;
+
+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;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.Assertions;
+
+
+class FirstOccurrenceOfAnIntegerTests {
+
+	@Test
+	public 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
+	public void whenUsingScanner_findFirstInteger() {
+		int i = new Scanner("ba31dung123").useDelimiter("\\D+").nextInt();
+		Assertions.assertEquals(31, i);
+	}
+
+	@Test
+	public 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
+	public void whenUsingCustomFunction_findFirstInteger() {
+		String str = "ba31dung123";
+		Integer i = FirstOccurrenceOfAnInteger.findFirstInteger(str);
+		Assertions.assertEquals(31, i);
+	}
+
+
+}