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Quizzes > Computers & Technology > Programming & Software

Ready to Ace the Ultimate Java Coding Quiz?

Think you can master our Java programming test? Jump into this Java online quiz!

Difficulty: Moderate
2-5mins
Learning OutcomesCheat Sheet
Paper art style Java code symbols data types exception handling icons quiz title on golden yellow background.

Ready to prove your prowess in Java? Take our free Java quiz challenge and dive into object-oriented fundamentals, exception handling, and API mastery. Whether you're brushing up on variables or debugging Java data types quiz scenarios, this engaging Java coding quiz pinpoints strengths and spots areas for growth. You'll tackle Java trivia questions, sharpen your syntax, and see how you fare on a quick Java programming test. This interactive Java online quiz delivers instant feedback and handy tips to boost your confidence. Feeling competitive? Compare your score with peers, revisit tricky concepts with our Java programming quiz , and emerge ready for real-world projects. Ready to level up? Let's get started!

What is the size of an int in Java?
16 bits
64 bits
32 bits
Depends on the platform
In Java, an int is always a 32-bit signed two's complement integer regardless of platform architecture. This ensures portability across different systems. You can verify this in the Java Language Specification. Oracle Docs
Which of the following is not a Java primitive type?
String
double
int
boolean
Java primitives include byte, short, int, long, float, double, boolean, and char. String is a class in java.lang and not a primitive type. Strings are immutable objects. Oracle Docs
What is the default value of a boolean instance variable in Java?
false
0
null
true
Instance variables of type boolean default to false if not explicitly initialized. Local variables don't have default values and must be initialized before use. This default is defined by the Java language specification. Java Language Spec
What is the result of the expression "5" + 3 in Java?
Type error
null3
53
8
The + operator with a String operand concatenates rather than adds. "5" + 3 produces the String "53". Numeric 3 is converted to its String representation. Oracle Docs
Which keyword is used to inherit from a superclass in Java?
extends
inherits
super
implements
In Java, the extends keyword indicates that a class is inheriting from a superclass. implements is used to adopt interfaces. super is used inside methods to refer to the parent class. Oracle Docs
Which method signature is the valid entry point for a standalone Java application?
public static void start(String[] args)
private void main(String[] args)
public void main()
public static void main(String[] args)
The JVM looks for public static void main(String[] args) as the program's entry point. The method must be public, static, return void, and accept a String array parameter. Any deviation prevents program launch. Oracle Tutorial
Are Java Strings mutable?
Only when created with new String()
Yes, always
No, Strings are immutable
Only in Java 9+
Strings in Java are immutable; once created, their value cannot change. Operations that appear to modify a String actually create a new instance. This immutability supports thread safety. Oracle Docs
Which of these correctly represents a char literal in Java?
'A'
'A'
"A"
`A`
Char literals in Java use single ASCII apostrophes (') around a single character. Double quotes denote Strings. Other quote styles are invalid in Java source. Oracle Docs
What is the default value of an object reference instance variable?
0
an empty object
null
 
Instance variables that are object references default to null if not explicitly initialized. This avoids dangling pointers but requires null checks. Local variables have no defaults and must be assigned before use. Java Language Spec
Which operator compares two primitive values for equality?
equalsIgnoreCase()
==
===
equals()
The == operator compares primitive values by value. equals() is a method for objects. === is not a Java operator. equalsIgnoreCase() is specific to String comparison ignoring case. Oracle Docs
What is the size of a long in Java?
128 bits
64 bits
Depends on OS
32 bits
A long in Java is a 64-bit signed two's complement integer on all platforms. It provides a larger range than int. Its size is fixed by the language specification. Oracle Docs
How do you declare an array of integers in Java?
int arr[] = new int;
array arr;
int[] arr;
int arr();
The correct syntax to declare an int array is int[] arr; or int arr[];. The other options are not valid Java declarations. Initialization with new int[size] is needed before use. Oracle Docs
Which keyword allows a class to implement an interface in Java?
extends
implements
inherits
uses
In Java, a class uses the implements keyword to adopt the contract defined by an interface. A class may implement multiple interfaces. extends is used only for class-to-class inheritance. Oracle Docs
Which of these best describes polymorphism in Java?
Same method name, same signature
One object, multiple classes
Changing data types at runtime
Ability of an object to take many forms
Polymorphism allows objects of different classes to be treated as objects of a common superclass or interface. It's realized via overriding and interfaces. This is fundamental to flexible and reusable code. Oracle Docs
What feature does try-with-resources provide?
Compile-time resource checking
Dynamic proxy creation
Automatic closing of resources
Checked exceptions avoidance
Try-with-resources automatically closes resources that implement AutoCloseable after the try block. It reduces boilerplate finally blocks. Introduced in Java 7, it enhances exception safety. Oracle Docs
Given List and List, which assignment is valid in Java?
List objs = new ArrayList();
List strs = new ArrayList();
List list = new ArrayList();
List objs = List;
List is a wildcard that can reference any generic List type. Generics are invariant, so List cannot reference List directly. Wildcards add flexibility while preserving type safety. Oracle Docs
What is autoboxing in Java?
Automatic conversion between primitive and wrapper types
Converting primitives to strings
Automatic conversion between primitive types
Wrapping code in boxes
Autoboxing automatically wraps primitives (e.g., int) into their wrapper classes (e.g., Integer) when needed. The reverse is unboxing. This feature introduced in Java 5 simplifies collection usage. Oracle Docs
Which compares two objects for content equality in Java?
==
compareTo()
equals()
equalsIgnoreCase()
The equals() method compares object contents if properly overridden. == checks reference identity, not content. compareTo() is for ordering in Comparable. equalsIgnoreCase() is specific to Strings. JavaDoc
What happens when you declare a class as final in Java?
It cannot be instantiated
It must contain a main method
All its methods become static
It cannot be subclassed
A final class cannot be extended by any other class, preventing inheritance. This is used for security and design reasons. Methods and fields inside can still be non-final. Oracle Docs
How do you define a method that accepts a variable number of int arguments?
void foo(int numbers[])
void foo(int... numbers)
void foo(int number*)
void foo(int[]... numbers)
Varargs syntax uses three dots after the type (int...). Inside the method, numbers is treated as an int array. It must be the last parameter if combined with others. Oracle Docs
Which loop is enhanced for iterating over collections in Java?
while (iterator.hasNext())
for (int i = 0; i < n; i++)
do { } while()
for (Type item : collection)
The enhanced for loop (for-each) uses the syntax for (Type item : collection). It simplifies iteration over arrays or Iterable types. It avoids manual iterator handling. Oracle Docs
What does the static import feature allow?
Use static members without class qualification
Override static methods
Import static inner classes only
Import only static variables
Static import allows you to reference static members without class name prefix. For example, import static java.lang.Math.*; lets you call sqrt() directly. It should be used judiciously. Oracle Docs
Which is a valid enum declaration in Java?
public class Color enum { RED, GREEN }
public enum Color { RED, GREEN, BLUE }
public enum Color [] { RED, GREEN }
enum Color = { RED, GREEN }
Enums are declared with the enum keyword, listing constants in braces. They implicitly extend java.lang.Enum. Incorrect syntax variants are not recognized by the compiler. Oracle Docs
Which exception must be caught or declared if thrown by a method?
NullPointerException
IOException
Error
RuntimeException
Checked exceptions like IOException must be either caught in a try-catch or declared in the method's throws clause. RuntimeExceptions and Errors are unchecked. This enforces error handling for recoverable conditions. Oracle Docs
What is true about the synchronized keyword on a static method?
Locks the Class object
Locks the instance
Is slower than volatile
Prevents deadlocks
Synchronizing a static method locks the Class object, not individual instances. This ensures only one thread executes any synchronized static method of that class at a time. It's useful for class-level resource protection. Oracle Docs
What does the volatile keyword guarantee?
Mutual exclusion
Atomicity of compound operations
Visibility of changes across threads
Higher performance than synchronized
Volatile ensures that reads and writes to the variable go directly to main memory, providing visibility guarantees across threads. It does not provide atomicity for compound actions. It's lighter than synchronized but less powerful. Oracle Docs
Which interface supports returning a result and throwing checked exceptions from a task?
Runnable
Supplier
Callable
Consumer
Callable has a call() method that returns a value of type V and can throw checked exceptions. Runnable's run() returns void and cannot throw checked exceptions. Callable is used with ExecutorService. JavaDoc
What role does ExecutorService play in Java concurrency?
Replaces volatile variables
Handles low-level I/O operations
Provides synchronized collections
Manages thread creation and task execution
ExecutorService abstracts thread management, providing a pool of threads to execute submitted tasks. It decouples task submission from execution policy. It supports lifecycle management and futures. JavaDoc
Which Stream operation is intermediate and returns another Stream?
filter()
count()
forEach()
toArray()
filter() is an intermediate operation that returns a new Stream with elements that match the predicate. Intermediate operations are lazy and build pipelines. forEach() and count() are terminal operations. JavaDoc
How do you write a lambda expression that adds two integers a and b?
(int a, int b) -> a + b
add(a, b) -> a + b
(a, b) -> return a + b
(int a, int b) => a + b
Lambda parameters can declare types or omit them if inferable. (int a, int b) -> a + b is valid and returns the sum. The arrow token is ->, not =>. return keyword is optional for single expressions. Oracle Docs
What is a method reference in Java?
Syntax shortcut to refer to a method via ::
A pointer to a method in JNI
A way to reference overloaded methods
Dynamic dispatch of methods
Method references use the :: operator to refer to existing methods or constructors. They are shorthand for lambdas that call a single method. For example, String::length. Oracle Docs
Which statement about inner classes is true?
They always require an instance of outer class
They can be instantiated without the outer class
They are always static
They cannot access outer final variables
Non-static inner classes hold a reference to an instance of the outer class and require it for instantiation. They can access all members of the outer class. Static nested classes do not have this requirement. Oracle Docs
What is required to use reflection to call a private method?
setAccessible(true) on the Method object
Compile with -reflect flag
Public API only
Method must be static
To invoke private methods via reflection, you must call setAccessible(true) on the Method object to bypass Java access checks. This requires appropriate security permissions. Oracle Docs
Which marker interface indicates an object can be serialized?
Serializable
Cloneable
Externalizable
Persistable
Serializable is a marker interface with no methods that tells the JVM an object can be serialized. Externalizable extends Serializable and requires implementing writeExternal/readExternal. Cloneable is for cloning. JavaDoc
Why is finalize() discouraged in Java?
Unreliable and unpredictable timing
Requires JNI to implement
It's never called
Always causes memory leaks
finalize() runs unpredictably before garbage collection and may not run at all. It adds performance overhead and complexity. Alternatives include try-with-resources and cleaners. JavaDoc
What is the parent-first delegation model in class loading?
Custom loaders override parent
Bootstrap loads before extension loaders
Child loader delegates to parent first
Classes loaded from the bottom of the hierarchy
In parent-first delegation, a class loader delegates loading requests to its parent before attempting to load the class itself. This prevents duplicate class definitions and ensures core classes are prioritized. Oracle Docs
What is the purpose of the Java Platform Module System (JPMS)?
To remove the JVM
To modularize the JDK and applications
To enforce single-threading
To replace Maven
JPMS (introduced in Java 9) modularizes the JDK and allows developers to create modules with explicit dependencies and exported APIs. It improves encapsulation, performance, and security. Oracle Docs
Which wildcard captures any type and is super to a given type?
? <: T
? |> T
? super T
? extends T
? super T accepts T and any of its supertypes, making it useful for writing to generics. extends is for covariance (reading). This is part of PECS (Producer Extends, Consumer Super). Oracle Docs
What is the ForkJoinPool used for?
Managing JDBC connections
Parallel divide-and-conquer tasks
Handling GUI events
Serializing objects
ForkJoinPool is designed for work-stealing parallelism, dividing tasks recursively and merging results. It's ideal for algorithms that can be broken into subtasks. Introduced in Java 7. JavaDoc
What does the Java Memory Model's happens-before guarantee ensure?
Infinite caching
Removal of data races automatically
Visibility and ordering of memory operations
Absolute atomicity of all operations
The happens-before relationship defines memory visibility and ordering constraints between threads. If one action happens-before another, the first's effects are visible to the second. It's core to thread safety. Java Memory Model
Which JVM argument allows you to select the garbage collector?
-cp
-XX:+UseG1GC
-Xmx
-jar
The -XX:+UseG1GC flag enables the G1 Garbage Collector. Other collectors can be selected similarly with -XX flags (e.g., UseParallelGC). -Xmx sets heap size, not collector choice. Oracle GC Tuning
0
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Study Outcomes

  1. Understand Core Java Concepts -

    Identify and explain fundamental elements such as data types, variables, and control flow featured in this Java quiz.

  2. Apply Object-Oriented Principles -

    Demonstrate how to implement classes, inheritance, and polymorphism using scenarios from the Java coding quiz.

  3. Analyze Exception Handling Scenarios -

    Interpret and resolve try-catch blocks and custom exceptions to improve code reliability in our Java programming test.

  4. Answer Java Trivia Questions -

    Recall and apply Java trivia questions to test your memory on language specifics and nuances.

  5. Review and Learn from Instant Feedback -

    Use detailed insights and feedback from the Java online quiz to pinpoint strengths and areas for growth.

  6. Prepare for Coding Interviews -

    Build confidence and readiness for technical interviews by tackling questions similar to those in a real-world Java quiz challenge.

Cheat Sheet

  1. Primitive Data Types and Variables -

    Oracle's Java Tutorial defines eight primitives (byte, short, int, long, float, double, boolean, char) as the building blocks of any Java program. Use the mnemonic "BSILFDBC" to recall them quickly and practice declaring each in a Java online quiz to gauge your comfort level (Oracle Docs). Understanding default values and type ranges is key for acing your Java quiz questions.

  2. Object-Oriented Principles (OOP) -

    Mastering OOP - encapsulation, inheritance, polymorphism, and abstraction - is vital for any Java programming test and Java coding quiz. Remember that "IS-A" represents inheritance (e.g., a Dog IS-A Animal) and "HAS-A" shows composition (e.g., a Car HAS-A Engine), as outlined in the Java Language Specification. Regularly sketch UML diagrams to visualize class hierarchies and method signatures for better retention.

  3. Exception Handling -

    Java's try-catch-finally construct helps manage runtime anomalies, with checked exceptions (e.g., IOException) enforced at compile-time and unchecked ones (e.g., NullPointerException) at runtime (Effective Java, Bloch). A quick snippet: try { /* code */ } catch (Exception e) { /* handler */ } finally { /* cleanup */ } boosts familiarity and confidence when tackling Java trivia questions on exception flows. Practice distinguishing between checked and unchecked in a mini Java coding quiz to solidify your understanding.

  4. Java Collections Framework -

    The Collections Framework organizes data with interfaces like List, Set, and Map - key for efficient data manipulation in any Java online quiz. For example, ArrayList allows duplicates and fast index access, while HashSet enforces uniqueness and offers constant-time operations (Java SE Docs). Experiment with common methods such as add(), remove(), and iterate() to master collection behaviors.

  5. JVM Architecture and Memory Management -

    Understanding the Java Virtual Machine - its stack, heap, and method areas - is crucial for deep insights in your Java programming test. Remember the mnemonic "Young-Old-Permanently" (Young Generation, Old Generation, Permanent Generation) to recall GC regions (Java Performance Tuning Guide). Tweak garbage collector flags (e.g., -Xms, -Xmx) to see how memory settings impact performance during hands-on practice.

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