D286 Java Fundamentals - Set 2 - Part 2

Correct Answer: Storing a resizable ordered collection of objects

ArrayList implements a resizable array of objects, providing fast index access and automatic growth as elements are added.

Correct Answer: ArrayList grows dynamically while an array has fixed size

An array's length is fixed at creation, whereas an ArrayList automatically resizes its internal storage as elements are added or removed.

Correct Answer: Set

A Set contains no duplicate elements. HashSet and TreeSet are common implementations, differing in ordering and performance characteristics.

Correct Answer: Key-value pairs with unique keys

A Map associates unique keys with values, allowing efficient retrieval of a value by its key. HashMap is the most commonly used implementation.

Correct Answer: Compile-time type safety avoiding casts at runtime

Generics let collections be parameterized with a type, so the compiler enforces type correctness and eliminates the need for explicit casts when retrieving elements.

Correct Answer: An event disrupting normal program flow that can be handled

An exception signals an abnormal condition during execution. Java's exception mechanism allows such conditions to be caught and handled rather than crashing the program.

Correct Answer: Checked exceptions must be declared or caught; unchecked need not be

Checked exceptions must be caught or declared with throws. Unchecked exceptions, which extend RuntimeException, impose no such compile-time requirement.

Correct Answer: NullPointerException

A NullPointerException is thrown when code attempts to dereference a variable holding null, such as calling a method on it.

Correct Answer: Executing cleanup code whether or not an exception was thrown

A finally block always executes after try and catch, making it the appropriate place to release resources such as files or database connections.

Correct Answer: Explicitly raises an exception from code

The throw statement explicitly raises an exception instance. The throws clause in a method declaration is separate and states which checked exceptions may propagate.

Correct Answer: Automatically closing resources that implement AutoCloseable

Try-with-resources declares resources in the try clause and closes them automatically when the block exits, eliminating verbose finally blocks and resource leaks.

Correct Answer: Attempting to parse a String that is not a valid number

NumberFormatException is thrown when a method such as Integer.parseInt() receives a String that cannot be converted to a numeric value.

Correct Answer: Reading input from sources such as the keyboard or files

Scanner parses primitive types and Strings from input sources, most commonly System.in for console input during learning and simple applications.

Correct Answer: Prints its argument to standard output followed by a newline

System.out.println() writes the given value to standard output and appends a line separator. System.out.print() omits the newline.

Correct Answer: Providing static methods for common mathematical operations

The Math class provides static methods such as abs(), pow(), sqrt(), and random(), along with constants PI and E.

Correct Answer: A double between 0.0 inclusive and 1.0 exclusive

Math.random() returns a pseudorandom double greater than or equal to 0.0 and strictly less than 1.0, which can be scaled to other ranges.

Correct Answer: A method belonging to the class that can be called without an instance

A static method belongs to the class rather than any instance and is invoked using the class name. It cannot access instance fields directly.

Correct Answer: No particular instance exists when a static method is invoked

Static methods belong to the class and may be called without any object, so there is no instance whose fields could be referenced without an explicit reference.

Correct Answer: A type representing a fixed set of named constants

An enum defines a type with a fixed set of named constant instances, providing type safety over using raw integers or Strings for such values.

Correct Answer: Clearer expression of selection among many discrete values

A switch statement expresses selection among many discrete values more clearly and compactly than a long chain of if-else comparisons on the same variable.