Java Full Stack with React Interview Questions in Mumbai

@ExtendWith(MockitoExtension.class) class ProductServiceTest { @Mock ProductRepository repo; @InjectMocks ProductService service; @Test void throwsWhenProductMissing() { when(repo.findById(1L)).thenReturn(Optional.empty()); assertThrows(ResourceNotFoundException.class, () -> service.getProduct(1L)); verify(repo).findById(1L); } }

function LoginForm({ onLogin }) { const [form, setForm] = useState({ email: '', password: '' }); const [errors, setErrors] = useState({}); const handleChange = e => setForm({ ...form, [e.target.name]: e.target.value }); const handleSubmit = e => { e.preventDefault(); const errs = {}; if (!/^\S+@\S+\.\S+$/.test(form.email)) errs.email = 'Enter a valid email'; if (form.password.length < 8) errs.password = 'Minimum 8 characters'; setErrors(errs); if (Object.keys(errs).length === 0) onLogin(form); }; return ( <form onSubmit={handleSubmit}> <input name="email" value={form.email} onChange={handleChange} /> {errors.email && <span>{errors.email}</span>} <input name="password" type="password" value={form.password} onChange={handleChange} /> {errors.password && <span>{errors.password}</span>} <button type="submit">Login</button> </form> ); }

SELECT e.name AS employee, e.salary, m.name AS manager, m.salary AS manager_salary FROM employees e JOIN employees m ON e.manager_id = m.id WHERE e.salary > m.salary; -- A self join treats the same table as two roles.

Map<String, Long> countByDept = employees.stream() .collect(Collectors.groupingBy( Employee::getDepartment, Collectors.counting())); // Average salary per department: Map<String, Double> avgSalary = employees.stream() .collect(Collectors.groupingBy( Employee::getDepartment, Collectors.averagingDouble(Employee::getSalary))); // Use TreeMap::new as the second argument to get sorted keys.

Path path = Path.of("data.txt"); try (BufferedReader reader = Files.newBufferedReader(path)) { String line; while ((line = reader.readLine()) != null) { System.out.println(line); } } catch (IOException e) { log.error("Could not read file", e); } // The reader is closed automatically, even if an exception occurs, // because BufferedReader implements AutoCloseable.

@GetMapping("/api/products") public Page<ProductDto> list( @RequestParam(defaultValue = "0") int page, @RequestParam(defaultValue = "20") int size, @RequestParam(defaultValue = "price") String sort) { Pageable pageable = PageRequest.of(page, Math.min(size, 100), Sort.by(sort).ascending()); return repository.findByActiveTrue(pageable).map(ProductDto::from); } // Repository: Page<Product> findByActiveTrue(Pageable pageable);

sealed interface Payment permits Card, Upi {} record Card(String number, double amount) implements Payment {} record Upi(String vpa, double amount) implements Payment {} static String describe(Payment p) { return switch (p) { case Card c when c.amount() > 50000 -> "High value card"; case Card c -> "Card ending " + c.number().substring(12); case Upi u -> "UPI to " + u.vpa(); }; } // Sealed types make the switch exhaustive without a default branch (Java 21).

# application.yml app: payment: timeout-ms: 3000 retry-count: 2 @ConfigurationProperties(prefix = "app.payment") @Validated public record PaymentProperties( @Min(500) int timeoutMs, @Max(5) int retryCount) {} @SpringBootApplication @EnableConfigurationProperties(PaymentProperties.class) public class App { } // Relaxed binding maps timeout-ms to timeoutMs automatically.

const original = { user: { name: 'Asha' }, tags: ['a'], joined: new Date() }; // Modern built-in (handles Date, Map, Set, cycles): const copy = structuredClone(original); // Spread is only a shallow copy: const shallow = { ...original }; shallow.user.name = 'Ravi'; // also changes original.user.name // JSON.parse(JSON.stringify(obj)) loses Dates, functions, // undefined and fails on circular references.

function ProductList() { const [products, setProducts] = useState([]); const [loading, setLoading] = useState(true); const [error, setError] = useState(null); useEffect(() => { const controller = new AbortController(); fetch('/api/products', { signal: controller.signal }) .then(res => { if (!res.ok) throw new Error('HTTP ' + res.status); return res.json(); }) .then(data => setProducts(data.content)) .catch(err => { if (err.name !== 'AbortError') setError(err.message); }) .finally(() => setLoading(false)); return () => controller.abort(); }, []); if (loading) return <p>Loading...</p>; if (error) return <p>Error: {error}</p>; return <ul>{products.map(p => <li key={p.id}>{p.name}</li>)}</ul>; }

.container { display: flex; justify-content: center; /* horizontal */ align-items: center; /* vertical */ min-height: 100vh; } /* Grid alternative */ .container { display: grid; place-items: center; min-height: 100vh; }