SCJP Java Generics, Enums, and Autoboxing

Question 1

What is the primary benefit of using generics in Java?

Accepted Answer

Type safety at compile time, eliminating the need for explicit casting

Answer

Generics allow type parameters to be specified at compile time, catching type errors early and eliminating the need for unsafe casts.

Question 2

What is type erasure in Java generics?

Accepted Answer

Removing type parameter information at compile time so the bytecode uses raw types

Answer

Java implements generics through type erasure: type parameters are removed at compile time and replaced with their bounds (or Object), so no generic type info exists at runtime.

Question 3

What does autoboxing in Java do?

Accepted Answer

Automatically converts primitive types to their wrapper class equivalents

Answer

Autoboxing is the automatic conversion of primitives (like `int`) to their wrapper classes (like `Integer`) when needed by the context.

Question 4

Which of the following correctly declares a generic method in Java?

Accepted Answer

public <T> T swap(T a, T b)

Answer

A generic method declares its type parameter `` before the return type: `public T methodName(...)`.

Question 5

What is an enum in Java?

Accepted Answer

A special class that represents a group of named constants

Answer

An `enum` is a special Java class that defines a fixed set of named constants, with the ability to have fields, methods, and constructors.

SCJP - Sun Certified Java Programmer Practice Test

SCJP - Sun Certified Java Programmer Practice Test

SCJP Java Generics, Enums, and Autoboxing