Basic Java

1. What does the BufferedReader.readLine() method return when there's nothing left to read?

An empty string

A special EOF character

null

Throws an EOFException

2. What will be the output of the following code?

enum Day { MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY, SUNDAY }
System.out.println(Day.MONDAY.ordinal());

0

1

6

MONDAY

3. What happens if you call Files.createDirectories() on a path where the directory already exists?

Nothing happens; no exception is thrown.

It throws FileAlreadyExistsException.

It deletes and recreates the directory.

It throws an exception because the parent directories cannot be verified.

4. Which class is recommended for building strings piece by piece in a loop?

String

StringBuffer

StringBuilder

StringJoiner

5. What will the resulting file contain after this code runs?

try (BufferedWriter w = new BufferedWriter(new FileWriter(path.toFile()))) {
    w.write("Line1");
    w.write("Line2");
}

Two separate lines: "Line1" and "Line2"

A single line: "Line1Line2"

Only "Line2"

The code throws an exception because newLine() was never called.

6. What is the primary characteristic of a String in Java?

Strings are mutable and can be changed after creation.

Strings are immutable and cannot be changed after creation.

Strings are primitive types in Java.

Strings can only contain single-byte characters.

7. What does it mean that Java arrays are covariant?

Arrays can hold mixed data types.

An Integer[] can be assigned to a Number[] variable.

Arrays can be resized dynamically.

Covariant arrays are always safe to use.

8. What happens when Files.copy(source, dest) is called and the destination file already exists?

It throws FileAlreadyExistsException.

It silently overwrites the destination.

It throws NoSuchFileException.

It appends the source file's content to the destination.

9. Identify the best practices when working with wrapper classes.

Always use equals() when comparing wrapper objects.

Assign null directly to primitive variables.

Use primitive types in tight loops instead of wrapper types.

Ignore NumberFormatException when parsing user input.

10. Which methods are used for replacing parts of a string?

replace()

replaceAll()

substring()

split()

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