SCJP Java String Handling and Regular Expressions 4

Question 1

What does the `String.format("%05d", 42)` call return?

Accepted Answer

"00042"

Answer

The format specifier `%05d` pads the integer with leading zeros to a total width of 5.

Question 2

Which `Pattern` flag makes `.` match newline characters in addition to all other characters?

Accepted Answer

Pattern.DOTALL

Answer

`Pattern.DOTALL` enables the `.` metacharacter to match any character including line terminators.

Question 3

Given `String s = "aabbcc"; s.replaceAll("(.)\1", "$1");`, what is the result?

Accepted Answer

"abc"

Answer

The regex `(.)\1` matches any character followed by itself (a backreference), and `$1` replaces the pair with a single instance.

Question 4

What is the output of `System.out.println("hello".indexOf('l', 4));`?

Accepted Answer

-1

Answer

`indexOf(char, fromIndex)` starts searching at index 4; since 'l' does not appear at index 4 or later in "hello", it returns -1.

Question 5

Which statement correctly creates a `StringBuilder` with an initial capacity of 50?

Accepted Answer

new StringBuilder(50)

Answer

The `StringBuilder(int capacity)` constructor creates a builder with the specified initial capacity.

SCJP - Sun Certified Java Programmer Practice Test