What error occurs when running this code, assuming 'data_to_skip.txt' is successfully created and closed?
java
import java.io.FileReader;
import java.io.IOException;
import java.io.File;
public class MyClass {
public static void main(String[] args) {
File file = new File("data_to_skip.txt");
try {
file.createNewFile();
FileReader reader = new FileReader(file);
reader.close(); // Close the reader
reader.skip(10); // Attempt to skip on a closed stream
System.out.println("Skipped 10 characters.");
} catch (IOException e) {
System.err.println("Error: " + e.getMessage());
} finally {
file.delete();
}
}
}
✅ Correct Answer: A) The program prints 'Error: Stream closed' and exits.
Similar to `read()`, calling `skip()` on a `FileReader` that has already been closed will result in an `IOException` with the message 'Stream closed'.
Q1582easycode output
What does this code print?
java
public class Main {
public static void main(String[] args) {
int[][] numbers = {{10, 20}, {30, 40}};
int sum = 0;
for (int[] row : numbers) {
for (int num : row) {
sum += num;
}
}
System.out.println(sum);
}
}
✅ Correct Answer: A) 100
The code iterates through all elements of the 2D array using enhanced for loops and adds them to `sum`. The sum will be 10 + 20 + 30 + 40 = 100.
Q1583easycode error
What type of error will occur when compiling or running this Java code snippet?
java
public class ArrayTest {
public static void main(String[] args) {
int[] values = {10, 20, 30};
System.out.println(values[3]);
}
}
✅ Correct Answer: C) ArrayIndexOutOfBoundsException
Arrays in Java are 0-indexed. For an array of size 3, valid indices are 0, 1, and 2. Accessing index 3 will cause an ArrayIndexOutOfBoundsException at runtime.
Q1584easy
Which of the following combinations is valid for a `try` block in Java?
✅ Correct Answer: C) A `try` block must be followed by at least one `catch` block OR a `finally` block.
A `try` block cannot stand alone; it must be accompanied by at least one `catch` block or a `finally` block (or both) to form a complete exception handling construct.
Q1585medium
Which of the following 2D array declarations and initializations is syntactically invalid in Java?
✅ Correct Answer: C) int[][] matrix = new int[][3];
When using `new` for a 2D array, if you specify the column dimension, you must also specify the row dimension. `new int[][3]` is invalid because the first dimension is missing while the second is present.
Q1586easy
Which annotation is typically used to explicitly mark an interface as a functional interface, although it's not strictly mandatory?
✅ Correct Answer: B) `@FunctionalInterface`
The `@FunctionalInterface` annotation is used to indicate that an interface is intended to be a functional interface. It helps the compiler enforce the single abstract method rule.
Q1587easycode error
What is the compilation error in the following Java code snippet?
java
public class LoopError {
public static void main(String[] args) {
int val = 0;
do {
System.out.println("Value: " + val++);
} while (val);
}
}
✅ Correct Answer: B) Incompatible types: `int` cannot be converted to `boolean` in `while` condition.
The condition of a `while` loop must be a boolean expression. Using an integer `val` directly as the condition, like `while (val)`, is a type mismatch error in Java because an `int` cannot implicitly be converted to a `boolean`.
Q1588mediumcode error
What is the compilation error in the provided Java code?
java
abstract class Vehicle {
abstract void start();
abstract void stop();
}
public class Car extends Vehicle {
void start() {
System.out.println("Car starts");
}
}
✅ Correct Answer: A) The type Car must implement the inherited abstract method Vehicle.stop()
A concrete class (Car) extending an abstract class (Vehicle) must implement all of its inherited abstract methods. Here, Car fails to implement the abstract method stop().
Q1589medium
When an unlabeled `break` statement is encountered within the innermost loop of a nested loop structure (e.g., `for (outer) { for (inner) { break; } }`), which loop does it terminate?
✅ Correct Answer: B) It terminates only the innermost loop.
An unlabeled `break` statement always terminates only the innermost enclosing loop or `switch` statement. It does not affect any outer loops in a nested structure.
Q1590mediumcode output
What is the output of this code?
java
class InvalidInputException extends Exception {
public InvalidInputException(String message) {
super(message);
}
}
public class Main {
public static void validate(int num) throws InvalidInputException {
if (num == 0) {
throw new InvalidInputException("Input cannot be zero.");
}
System.out.println("Validation successful.");
}
public static void main(String[] args) {
try {
validate(10);
validate(0);
} catch (InvalidInputException e) {
System.out.println("Caught in main: " + e.getMessage());
}
}
}
✅ Correct Answer: A) Validation successful.
Caught in main: Input cannot be zero.
The first `validate(10)` call succeeds and prints. The second `validate(0)` call throws `InvalidInputException`, which is caught by the `catch` block in `main`, printing its message. The execution stops after the exception is caught.
Q1591hardcode error
What kind of error will occur when executing the following Java code?
java
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.Queue;
public class QError4 {
public static void main(String[] args) {
Queue<String> clq = new ConcurrentLinkedQueue<>();
clq.add("first");
clq.add(null);
System.out.println(clq.poll());
}
}
✅ Correct Answer: A) java.lang.NullPointerException
ConcurrentLinkedQueue, like many concurrent collections, does not permit null elements. Attempting to add a null element will result in a java.lang.NullPointerException.
Q1592medium
What is the primary benefit of using primitive functional interfaces (e.g., `IntPredicate`, `LongFunction`, `DoubleConsumer`) over their generic counterparts (e.g., `Predicate<Integer>`, `Function<Long, R>`, `Consumer<Double>`)?
✅ Correct Answer: A) They avoid autoboxing/unboxing overhead, leading to better performance for primitive types.
Primitive functional interfaces are specifically designed to operate directly on primitive types, thereby eliminating the performance overhead caused by autoboxing and unboxing operations between primitives and their wrapper objects.
Q1593easy
Which keyword marks the beginning of the loop body in a do-while loop?
✅ Correct Answer: A) do
The 'do' keyword precedes the block of code that forms the loop body, which is guaranteed to execute at least once.
Q1594easycode output
What does this Java code print?
java
class IDGenerator {
static int nextId = 1;
int id;
IDGenerator() {
id = nextId++;
System.out.println("Assigned ID: " + id);
}
}
public class Main {
public static void main(String[] args) {
IDGenerator gen1 = new IDGenerator();
IDGenerator gen2 = new IDGenerator();
IDGenerator gen3 = new IDGenerator();
}
}
The `nextId` is a static variable, incremented after assignment (`nextId++`) in each constructor call. Each new object gets the then-current value of `nextId` before it is incremented for the next object.
Q1595mediumcode output
What does this code print?
java
import java.util.HashMap;
public class Test {
public static void main(String[] args) {
HashMap<Integer, String> map = new HashMap<>();
map.put(1, "ValueA");
map.putIfAbsent(1, "ValueB"); // Key 1 already exists
map.putIfAbsent(2, "ValueC"); // Key 2 does not exist
System.out.println(map.get(1) + ", " + map.get(2));
}
}
✅ Correct Answer: A) ValueA, ValueC
`putIfAbsent()` inserts the specified value only if the specified key is not already associated with a value. For key 1, 'ValueA' remains. For key 2, 'ValueC' is inserted.
Q1596medium
What is the primary difference in performance characteristics between `ArrayList` and `LinkedList` in Java for adding/removing elements in the middle of the list?
✅ Correct Answer: B) `LinkedList` is generally faster for middle insertions/deletions because it only requires updating a few pointers.
`LinkedList` uses a doubly linked list structure, making middle insertions/deletions efficient (O(1) after finding the position) as only pointers need to be updated. `ArrayList`, being an array, requires shifting subsequent elements (O(n)).
Q1597easy
How many bits does the `int` primitive data type occupy in Java?
✅ Correct Answer: C) 32 bits
An `int` in Java is a 32-bit signed two's complement integer.
Q1598medium
What is the return type of the `reduce()` operation when provided with an identity and an accumulator (e.g., `stream.reduce(0, (a, b) -> a + b)`)?
✅ Correct Answer: C) T (the type of the elements and identity)
When an identity element is provided to `reduce()`, the operation guarantees a non-empty result (the identity value if the stream is empty), thus it returns `T` directly, not an `Optional<T>`.
Q1599easycode error
What is the error in this Java code?
java
import java.io.FileWriter;
import java.io.IOException;
public class FileWriterError9 {
public static void main(String[] args) throws IOException {
FileWriter writer = new FileWriter("mydata.txt");
writer.write("First line.\n");
writer.close();
// Attempting to write after closing the writer
writer.write("Second line.");
}
}
✅ Correct Answer: A) Attempting to `write()` to a `FileWriter` object after it has been `close()`d will result in an `IOException`.
Once a stream like `FileWriter` is closed, it cannot be used for further I/O operations. Any attempt to write to a closed `FileWriter` will result in an `IOException` (specifically, 'Stream closed'). To write again, a new `FileWriter` instance must be created.
Q1600easycode error
What kind of error will occur when executing the following Java code?
java
public class Sleeper {
public static void main(String[] args) {
Thread.sleep(1000); // Attempt to sleep without handling InterruptedException
System.out.println("Slept for 1 second.");
}
}
✅ Correct Answer: B) Compilation Error: Unhandled exception type InterruptedException.
The `Thread.sleep()` method throws a checked exception, `InterruptedException`. Java requires checked exceptions to be either caught using a `try-catch` block or declared in the method signature using `throws InterruptedException`.