[BAEL-8927] Guide to Objects.requireNonNull() in Java (#18099)

* [BAEL-8927] Guide to Objects.requireNonNull() in Java
 - add JUnit test

* [BAEL-8927] Guide to Objects.requireNonNull() in Java
 - replace sout with logger

* [BAEL-8927] Guide to Objects.requireNonNull() in Java
 - move to a module with the latest Java version

Author: martin-blazevic

core-java-modules/core-java-23/src/test/java/com/baeldung/requirenonnull/RequireNonNullUnitTest.java

@@ -0,0 +1,89 @@
+package com.baeldung.requirenonnull;
+
+import java.time.Instant;
+import java.util.Objects;
+import java.util.Random;
+import java.util.UUID;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+class RequireNonNullUnitTest {
+
+    private static final Logger logger = LoggerFactory.getLogger(RequireNonNullUnitTest.class);
+
+    void greet(String name) {
+        Objects.requireNonNull(name, "Name cannot be null");
+        logger.info("Hello, {}!", name);
+    }
+
+    @Test
+    void givenObject_whenGreet_thenNoException() {
+        Assertions.assertDoesNotThrow(() -> greet("Baeldung"));
+    }
+
+    @Test
+    void givenNull_whenGreet_thenException() {
+        Assertions.assertThrows(NullPointerException.class, () -> greet(null));
+    }
+
+    static class User {
+
+        private final String username;
+        private final String password;
+
+        public User(String username, String password) {
+            this.username = Objects.requireNonNull(username, "Username is null!");
+            this.password = Objects.requireNonNull(password, "Password is null!");
+        }
+
+        public String getUsername() {
+            return username;
+        }
+
+        public String getPassword() {
+            return password;
+        }
+    }
+
+    @Test
+    void givenValidInput_whenNewUser_thenNoException() {
+        Assertions.assertDoesNotThrow(() -> new User("Baeldung", "Secret"));
+    }
+
+    @Test
+    void givenNull_whenNewUser_thenException() {
+        Assertions.assertThrows(NullPointerException.class, () -> new User(null, "Secret"));
+        Assertions.assertThrows(NullPointerException.class, () -> new User("Baeldung", null));
+    }
+
+    void processOrder(UUID orderId) {
+        Objects.requireNonNull(orderId, () -> {
+            String message = "Order ID cannot be null! Current timestamp: " + getProcessTimestamp();
+            message = message.concat("Total number of invalid orders: " + getOrderAmount());
+            message = message.concat("Please provide a valid order.");
+            return message;
+        });
+        logger.info("Processing order with id: {}", orderId);
+    }
+
+    private static int getOrderAmount() {
+        return new Random().nextInt(100_000);
+    }
+
+    private static Instant getProcessTimestamp() {
+        return Instant.now();
+    }
+
+    @Test
+    void givenObject_whenProcessOrder_thenNoException() {
+        Assertions.assertDoesNotThrow(() -> processOrder(UUID.randomUUID()));
+    }
+
+    @Test
+    void givenNull_whenProcessOrder_thenException() {
+        Assertions.assertThrows(NullPointerException.class, () -> processOrder(null));
+    }
+}