feat: added Java Assignment Solutions (streams, optionals, records, sealed types)

Solutions/assignment/vishwas/Q1_NotificationService.java

@@ -0,0 +1,40 @@
+package assignment.vishwas;
+
+public class Q1_NotificationService {
+
+    interface NotificationService{
+        void send(String message);
+
+        default void sendWithRetry(String message,int retries){  // Used for Backward Compatibility
+            if(retries<0){
+                throw new IllegalArgumentException("Retry count cannot be negative.");
+            }
+            for(int attempt=1;attempt<=retries+1;attempt++){ // First Attempt + Additional attempts after failure
+                try {
+                    send(message);
+                    System.out.println("Message sent on attempt: " + attempt);
+                    return;
+                }
+                catch (Exception e) {
+                    if(attempt>retries){
+                        throw new RuntimeException("Failed sending message.");
+                    }
+                }
+
+            }
+        }
+    }
+
+    public static void main(String[] args) {
+        NotificationService notificationService = new NotificationService() {
+            @Override
+            public void send(String message) {
+                if(message==null){
+                    throw new RuntimeException("Message cannot be null.");
+                }
+                System.out.println("Sending message: " + message);
+            }
+        };
+        notificationService.sendWithRetry("Hello Cloudsufi!",3);
+    }
+}

Solutions/assignment/vishwas/Q2_StringValidator.java

@@ -0,0 +1,26 @@
+package assignment.vishwas;
+
+public class Q2_StringValidator {
+    @FunctionalInterface
+    public interface stringValidator {
+        boolean isValid(String str);
+    }
+    public static boolean validate(String str, stringValidator validator) {  // Utility Method
+        return validator.isValid(str);
+    }
+
+    public static void main(String[] args) {
+        String test = "Hello Cloudsufi!";
+
+        boolean isNonEmpty = validate(test,s->s!=null && !s.isEmpty());
+        System.out.println("Is String Non-Empty?: " + isNonEmpty);
+
+        boolean isLengthGreaterThan5 = validate(test,s->s!=null && s.length()>5);
+        System.out.println("Is String Length Greater than 5?: " + isLengthGreaterThan5);
+
+        boolean isStartingWithCapitalLetter = validate(test,s->s!=null && !s.isEmpty() && Character.isUpperCase(s.charAt(0)));
+        System.out.println("Is String starting with a Capital Letter?: " + isStartingWithCapitalLetter);
+
+
+    }
+}

Solutions/assignment/vishwas/Q3_Stream.java

@@ -0,0 +1,28 @@
+package assignment.vishwas;
+import java.util.List;
+
+public class Q3_Stream {
+    static class User {
+        String name;
+        int age;
+        public User(String name,int age){
+            this.name=name;
+            this.age=age;
+        }
+    }
+
+    static void main(String[] args) {
+        List<User> users = List.of(
+                new User("Vishwas",22),
+                new User("Aakash",21),
+                new User("Himani",23)
+        );
+
+        List <String> filteredAndSorted = users.stream()
+                .filter(user->user.age>18)
+                .map(user -> user.name.toUpperCase())
+                .sorted()
+                .toList();
+        System.out.println(filteredAndSorted);
+    }
+}

Solutions/assignment/vishwas/Q4_Predicates.java

@@ -0,0 +1,19 @@
+package assignment.vishwas;
+import java.util.Arrays;
+import java.util.List;
+import java.util.function.Predicate;
+
+public class Q4_Predicates {
+    static void main(String[] args) {
+        List<Integer> numbers = Arrays.asList(-5, -2, 0, 1, 2, 3, 4, 6, 9);
+
+        Predicate<Integer> isPositive = n -> n > 0;
+        Predicate<Integer> isEven = n -> n%2 == 0;
+
+        Predicate<Integer> isPositiveAndEven = isPositive.and(isEven);
+
+        numbers.stream()
+                .filter(isPositiveAndEven)
+                .forEach(System.out::println);
+    }
+}

Solutions/assignment/vishwas/Q5_Optional.java

@@ -0,0 +1,28 @@
+package assignment.vishwas;
+
+import java.util.Optional;
+
+public class Q5_Optional {
+    record User(String username, boolean isActive) {}
+
+    static Optional <User> findUser(String id) {
+        if("101".equals(id)){
+            return Optional.of(new User("vishwas",true));
+        } else if ("102".equals(id)) {
+            return Optional.of(new User("keshav",false));
+        }
+        else return Optional.empty();
+    }
+    static void userProcessor(String id){
+        findUser(id)
+                .filter(User::isActive)
+                .map(User::username)
+                .ifPresentOrElse(System.out::println,()-> System.out.println("User not found"));
+
+    }
+    static void main(String[] args) {
+        userProcessor("101");
+        userProcessor("102");
+        userProcessor("104");
+    }
+}

Solutions/assignment/vishwas/Q6_Records.java

@@ -0,0 +1,19 @@
+package assignment.vishwas;
+
+public class Q6_Records {
+    record Employee(Integer id, Integer salary){
+        public Employee{
+            if(salary<0){
+                throw new IllegalArgumentException("Salary must be greater than zero");
+            }
+        }
+        public boolean isHigherEarner(){
+            return salary>100000;
+        }
+    }
+
+    static void main(String[] args) {
+        Employee emp = new Employee(1035, 50000);
+        System.out.println(emp.salary());
+    }
+}

Solutions/assignment/vishwas/Q7_PaymentSystem.java

@@ -0,0 +1,46 @@
+package assignment.vishwas;
+
+public class Q7_PaymentSystem {
+    sealed interface Payment permits CardPayment, UpiPayment{
+    }
+
+    static final class CardPayment implements Payment{
+        private final String cardNumber;
+
+        CardPayment(String cardNumber){
+            this.cardNumber=cardNumber;
+        }
+
+        String getCardNumber(){
+            return cardNumber;
+        }
+    }
+    static final class UpiPayment implements Payment{
+        private final String upiId;
+
+        UpiPayment(String upiId){
+            this.upiId=upiId;
+        }
+
+        String getUpiId(){
+            return upiId;
+        }
+    }
+
+    static void process(Payment pmt){
+        if(pmt instanceof CardPayment card){
+            System.out.println("Processing Card Payment for card no.: "+card.getCardNumber());
+        }
+        else if(pmt instanceof UpiPayment upi){
+            System.out.println("Processing UPI Payment for UPI ID: "+upi.getUpiId());
+        }
+        else{
+            throw new IllegalStateException("Invalid Payment Type");
+        }
+    }
+
+    static void main(String[] args) {
+        process(new CardPayment("1234-5678-9101-3476"));
+        process(new UpiPayment("9876776541@upi"));
+    }
+}

Solutions/assignment/vishwas/Q8_TextBlocks.java

@@ -0,0 +1,21 @@
+package assignment.vishwas;
+
+public class Q8_TextBlocks {
+    public static void main(String[] args) {
+        String userId = "U3012";
+
+        String query = """
+            Select
+                id,
+                username,
+                email,
+                status
+            FROM users
+            WHERE id='%s'
+              AND status = 'ACTIVE'
+            ORDER BY username
+        """.formatted(userId);
+
+        System.out.println(query);
+    }
+}