Java String Handling and Regular Expressions Flashcards

What is the result of the following code? String s = "Hello"; s.concat(" World"); System.out.println(s);

Answer: Hello

String objects are immutable; concat() returns a new String but the result is not assigned back to s, so s remains "Hello".

Which of the following creates a String object in the string pool?

Answer: String s = "hello"

String literals (String s = "hello") are stored in the string pool, while using new String() always creates an object on the heap.

What does the == operator compare when used between two String objects?

Answer: The reference (memory address) of the objects

== compares object references, not content; use equals() to compare String content.

Which class provides a thread-safe, mutable sequence of characters?

Answer: StringBuffer

StringBuffer is synchronized, making it thread-safe, whereas StringBuilder is faster but not thread-safe.

What is the output of: System.out.println("abc".indexOf('c'));

Answer: 2

indexOf() returns the zero-based index; 'a' is at 0, 'b' at 1, 'c' at 2.

What is printed by: System.out.println("Hello World".substring(6));

Answer: World

substring(6) returns characters from index 6 to the end; index 6 is 'W', yielding "World".

Which method correctly checks whether a String starts with a given prefix?

Answer: startsWith()

The correct method name is startsWith(), which returns true if the string begins with the specified prefix.