Given public class Main { public static void main (String[] args) { try (BufferedReader br = new BufferedReader(new InputStreamReader(System.in))) { System.out.print("Input: "); String input =…

The correct answer is C. Input: Helloworld. Option C is marked correct, but this question actually contains a subtlety worth examining carefully - D is technically the more accurate answer, and this appears to be a flawed exam key. What the code actually does: The program ignores args entirely and reads from System.in…

Java I/O API

Question

Given
public class Main {
public static void main (String[] args) {
try (BufferedReader br = new BufferedReader(new InputStreamReader(System.in))) {
System.out.print("Input: ");
String input = br.readLine();
System.out.println("Echo: " + input);
} catch (IOException e) {
e.printStackTrace();
}
}
}
And the command:
java Main Helloworld
What is the result ?

Options

AInput: Echo: Helloworld
BInput: Echo: Helloworld Echo: Helloworld
CInput: Helloworld
DInput: Program will block until any input comes from System.in.
EA NullPointerException is thrown at run time.

How the community answered

(54 responses)

A
13% (7)
B
2% (1)
C
78% (42)
D
6% (3)
E
2% (1)

Explanation

Option C is marked correct, but this question actually contains a subtlety worth examining carefully - D is technically the more accurate answer, and this appears to be a flawed exam key.

What the code actually does: The program ignores args entirely and reads from System.in (the keyboard). When you run java Main Helloworld, "Helloworld" is a command-line argument stored in args[0], which is never accessed. The program prints "Input: " and then blocks indefinitely waiting for keyboard input - making D the correct real-world behavior.

Why each distractor fails:

A (Input: Echo: Helloworld) - incorrect formatting; System.out.print doesn't add a newline, but println would put "Echo:" on a new line, not the same line as "Input:"
B - there's no logic to print anything twice
C (Input: Helloworld) - only plausible if you consider the terminal echoing a user's typed "Helloworld" on the same line as "Input: "; but this omits the subsequent "Echo:" line the program would also print
E - no NullPointerException; even if readLine() returns null at EOF, string concatenation with null is valid in Java

Memory tip: When you see System.in in Java code, ask yourself: "Where is the data coming from?" Command-line arguments go to args[], not System.in. If the code reads System.in but the user passes args, those args are silently ignored.

Topics

#try-with-resources#BufferedReader#System.in#command-line args vs input streams

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