1. Why Does Compilation Fail?

The error is in this line:

java

final Stream strings = Files.readAllLines(Paths.get("orders.csv"));

Files.readAllLines(Paths.get("orders.csv")) returns a List<String>,not a Stream<String>.

A List cannot be assigned to a Stream.

2. Correcting the Code

The correct way to create a stream from the file:

java

Stream strings = Files.lines(Paths.get("orders.csv"));

This correctly creates a Stream from the file.

3. Expected Output After Fixing

java

Files.lines(Paths.get("orders.csv"))

skip(1) // Skips the header row

limit(2) // Limits to first two data rows

forEach(System.out::println);

Output:

arduino

1,Kylian Mbappé,Keyboard,2,25.50

2,Teddy Riner,Mouse,1,15.99

Thus, the correct answer is:Compilation fails.

References:

Java SE 21 - Files.readAllLines

Java SE 21 - Files.lines

Understanding the do-while Loop

The do-while loopexecutes at least oncebefore checking the condition.

The condition i++ > 0 increments iafterchecking.

Step-by-Step Execution

Iteration 1:

i = 0

Prints: "Chanel"

i++ updates i to 1

Condition 1 > 0is true, so the loop exits.

Why Doesn't the Loop Continue?

Since i starts at 0, the conditioni++ > 0 is false after the first iteration.

The loopexits immediately after printing "Chanel".

Final Output

nginx

Chanel

Thus, the correct answer is:Chanel

References:

Java SE 21 - do-while Loop

Java SE 21 - Post-Increment Behavior

In Java, the Stream API provides several methods to create streams. However, not all approaches are valid.

In this code, two Optional objects are created:

o1 is an empty Optional.

o2 is an Optional containing the integer 1.

A stream is created from o1 and o2. The filter method retains only the Optional instances that are present (i.e., non-empty). This results in a stream containing only o2.

The findAny method returns an Optional describing some element of the stream, or an empty Optional if the stream is empty. Since the stream contains o2, findAny returns Optional[Optional[1]].

The flatMap method is then used to flatten this nested Optional. It applies the provided mapping function (o -> o) to the value, resulting in Optional[1].

Finally, o3.orElse(2) returns the value contained in o3 if it is present; otherwise, it returns 2. Since o3 contains 1, the output is 1.

Understanding ExecutorService Methods

execute(Runnable command)

Runs the task but only supports Runnable (not Callable).

❌execService.execute(task2); fails because task2 is Callable.

submit(Runnable task)

Submits a Runnable task for execution.

execService.submit(task1); executes "Executing Task-1".

submit(Callable<T> task)

Submits a Callable task for execution.

execService.submit(task2); executes "Executing Task-2".

call() Does Not Exist in ExecutorService

❌execService.call(task1); and execService.call(task2); are invalid.

run() Does Not Exist in ExecutorService

❌execService.run(task1); and execService.run(task2); are invalid.

Correct Code to Print Both Messages:

java

execService.submit(task1);

execService.submit(task2);

Thus, the correct answer is:execService.submit(task1); execService.submit(task2);

References:

Java SE 21 - ExecutorService

Java SE 21 - Callable and Runnable

In this code, a Stream containing the elements "a" and "b" is processed using the collect method. The collect method is a terminal operation that performs a mutable reduction on the elements of the stream using a Collector. In this case, custom implementations for the supplier, accumulator, and combiner are provided.

Components of the collect Method:

Supplier:

() -> new StringBuilder("c")

This supplier creates a new StringBuilder initialized with the string "c".

Accumulator:

StringBuilder::append

This accumulator appends each element of the stream to the StringBuilder.

Combiner:

(a, b) -> b.append(a)

This combiner is used in parallel stream operations to merge two StringBuilder instances. It appends the contents of a to b.

Execution Flow:

Stream Elements:"a", "b"

Initial StringBuilder:"c"

Accumulation:

The first element "a" is appended to "c", resulting in "ca".

The second element "b" is appended to "ca", resulting in "cab".

Combiner:

In this sequential stream, the combiner is not utilized. The combiner is primarily used in parallel streams to merge partial results.

Final Result:

The StringBuilder contains "cab". Therefore, the output of the program is:

nginx

cab

In this code, three static methods from the Boolean class are used: logicalAnd, logicalOr, and logicalXor. Each method takes two boolean arguments and returns a boolean result based on the respective logical operation.

Evaluation of Each Statement:

Boolean.logicalAnd(1 == 1, 2 < 1)

Operands:

1 == 1 evaluates to true.

2 < 1 evaluates to false.

Operation:

Boolean.logicalAnd(true, false) performs a logical AND operation.

The result is false because both operands must be true for the AND operation to return true.

Output:

System.out.print(false); prints false.

Boolean.logicalOr(1 == 1, 2 < 1)

Operands:

1 == 1 evaluates to true.

2 < 1 evaluates to false.

Operation:

Boolean.logicalOr(true, false) performs a logical OR operation.

The result is true because at least one operand is true.

Output:

System.out.print(true); prints true.

Boolean.logicalXor(1 == 1, 2 < 1)

Operands:

1 == 1 evaluates to true.

2 < 1 evaluates to false.

Operation:

Boolean.logicalXor(true, false) performs a logical XOR (exclusive OR) operation.

The result is true because exactly one operand is true.

Output:

System.out.print(true); prints true.

Combined Output:

Combining the outputs from each statement, the final printed result is:

nginx

falsetruetrue