BAEL-7176: How to avoid NoSuchElementException with Stream (#15098)

Author: azhwani

core-java-modules/core-java-streams-5/src/test/java/com/baeldung/nosuchelementexception/NoSuchElementExceptionStreamUnitTest.java

@@ -0,0 +1,62 @@
+package com.baeldung.nosuchelementexception;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.List;
+import java.util.NoSuchElementException;
+import java.util.Optional;
+
+import org.junit.Test;
+
+public class NoSuchElementExceptionStreamUnitTest {
+
+    @Test(expected = NoSuchElementException.class)
+    public void givenEmptyOptional_whenCallingGetMethod_thenThrowNoSuchElementException() {
+        List<String> names = List.of("William", "Amelia", "Albert", "Philip");
+        Optional<String> emptyOptional = names.stream()
+          .filter(name -> name.equals("Emma"))
+          .findFirst();
+
+        emptyOptional.get();
+    }
+
+    @Test
+    public void givenEmptyOptional_whenUsingIsPresentMethod_thenReturnDefault() {
+        List<String> names = List.of("Tyler", "Amelia", "James", "Emma");
+        Optional<String> emptyOptional = names.stream()
+          .filter(name -> name.equals("Lucas"))
+          .findFirst();
+
+        String name = "unknown";
+        if (emptyOptional.isPresent()) {
+            name = emptyOptional.get();
+        }
+
+        assertEquals("unknown", name);
+    }
+
+    @Test
+    public void givenEmptyOptional_whenUsingOrElseMethod_thenReturnDefault() {
+        List<String> names = List.of("Nicholas", "Justin", "James");
+        Optional<String> emptyOptional = names.stream()
+          .filter(name -> name.equals("Lucas"))
+          .findFirst();
+
+        String name = emptyOptional.orElse("unknown");
+
+        assertEquals("unknown", name);
+    }
+
+    @Test
+    public void givenEmptyOptional_whenUsingOrElseGetMethod_thenReturnDefault() {
+        List<String> names = List.of("Thomas", "Catherine", "David", "Olivia");
+        Optional<String> emptyOptional = names.stream()
+          .filter(name -> name.equals("Liam"))
+          .findFirst();
+
+        String name = emptyOptional.orElseGet(() -> "unknown");
+
+        assertEquals("unknown", name);
+    }
+
+}