1Z0-811 What is Java Practice Test 3 — 15 Questions

Question 1

Which THREE are valid components of the Java Virtual Machine (JVM)?

Accepted Answer

Heap memory area. The JVM's runtime data areas include the heap memory area (C), which stores all class instances and arrays and is shared across threads, making it a core internal component of the JVM. The execution engine (D) is also a fundamental JVM component: it executes bytecode via an interpreter, and may include a JIT compiler and garbage collector. The class loader subsystem (E) is the JVM component responsible for loading, linking, and initializing classes (bootstrap, extension/platform, and application class loaders), so it is likewise a valid JVM component. By contrast, Java source code (.java files) (A) is human-readable input to the compiler, not part of the JVM, and the Java compiler javac (B) is a separate JDK tool that produces bytecode before the JVM is involved, so neither belongs to the JVM's internal architecture.

Answer

Java source code (.java files)

Answer

Java compiler (javac)

Question 2

What is the most likely cause of this error?

Accepted Answer

The heap size is insufficient for the objects being created.. The error in question is java.lang.OutOfMemoryError: Java heap space, which is thrown when the JVM cannot allocate an object in the heap because the heap is full and garbage collection cannot free enough memory. This directly indicates that the heap size is insufficient for the objects being created, either due to a genuine need for more memory or a memory leak within the Java heap. The other options describe different error conditions that produce different messages or exceptions.

Answer

There is a memory leak in native code outside the heap.

Answer

There is a stack overflow in the method being called.

Answer

Too many threads are running concurrently.

Question 3

A company wants to develop a Java application that can run on Windows, Linux, and macOS without any code changes. Which Java feature makes this possible?

Accepted Answer

Platform Independence via JVM. Java achieves platform independence through the JVM: source code is compiled to bytecode (.class files), which is platform-neutral, and each platform (Windows, Linux, macOS) has its own JVM implementation that interprets or JIT-compiles that bytecode to native instructions. This 'write once, run anywhere' capability is the core Java feature that lets the same compiled application run unchanged across operating systems.

Answer

Multithreading

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Garbage Collection

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Object-Oriented Programming

Question 4

A developer compiles a Java program successfully but gets 'ClassNotFoundException' when running it. What is the most likely cause?

Accepted Answer

The classpath does not include the directory containing the .class file. ClassNotFoundException occurs when the JVM cannot find the class definition, typically due to the classpath not including the location of the .class file. Option A is wrong because Java version incompatibility leads to UnsupportedClassVersionError, not ClassNotFoundException. Option B is wrong because an incorrect main method signature causes NoSuchMethodError. Option C is wrong because having multiple classes does not cause ClassNotFoundException unless one of them is missing from the classpath.

Answer

The Java version is incompatible

Answer

The main method signature is incorrect

Answer

The program has multiple classes

Question 5

Which component of the Java platform is responsible for executing compiled bytecode?

Accepted Answer

JVM. The JVM (Java Virtual Machine), option B, is the component that actually loads and executes compiled Java bytecode, interpreting it or JIT-compiling it to native machine code at runtime. It provides the runtime environment for bytecode execution, including class loading, memory management, and garbage collection. The JRE (option A) is a broader runtime package that includes the JVM plus core class libraries, so it is not the specific execution engine itself. The JDK (option C) is a development kit containing the JRE plus tools like javac, and the Java Compiler (option D) only translates source code into bytecode rather than executing it.

Answer

JRE

Answer

JDK

Answer

Java Compiler

Question 6

A company is upgrading from Java 8 to Java 11. Which advantage does the module system introduced in Java 9 provide?

Accepted Answer

Stronger encapsulation of internal APIs. The Java Platform Module System (JPMS, JSR 376) introduced in Java 9 allows libraries to explicitly export only public API packages via module-info.java, hiding internal packages like sun.misc and com.sun.* from reflective and compile-time access. This stronger encapsulation improves security and maintainability by preventing applications from depending on unsupported internal APIs. It is the headline benefit of modularization.

Answer

Better multithreading

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Faster garbage collection

Answer

Improved lambda syntax

Question 7

A developer writes a multi-threaded application that runs on Windows. To ensure the same bytecode runs without modification on Linux and macOS, which Java feature is essential?

Accepted Answer

Platform independence via JVM. Platform independence via JVM. The Java Virtual Machine (JVM) abstracts the underlying operating system and hardware, so bytecode compiled on any platform can run on any other platform that has a compatible JVM. This allows the same bytecode to run on Windows, Linux, and macOS without modification. Option A (Bytecode verification) is a security check that validates bytecode before execution, but it does not provide cross-platform portability. Option C (Just-in-Time compilation) optimizes performance by compiling bytecode to native code at runtime, but it is not essential for platform independence. Option D (Thread synchronization) is a concurrency control mechanism that prevents race conditions, but it does not affect cross-platform execution.

Answer

Bytecode verification

Answer

Just-in-Time (JIT) compilation

Answer

Thread synchronization

Question 8

An application throws 'java.lang.OutOfMemoryError: Java heap space'. Which JVM option can help generate diagnostic information to identify the cause?

Accepted Answer

-XX:+HeapDumpOnOutOfMemoryError. XX:+HeapDumpOnOutOfMemoryError instructs the JVM to generate a heap dump file when an OutOfMemoryError occurs, which can be analyzed to identify memory leaks or other causes. Option A (-version) prints the Java version and does not help with diagnostics. Option B (-verbose:gc) prints garbage collection details but does not produce a heap dump at the time of failure. Option D (-Xmx) sets the maximum heap size, which may delay or prevent the error but does not provide diagnostic information about the cause.

Answer

-version

Answer

-verbose:gc

Answer

-Xmx

Question 9

Which TWO are true about the Java Runtime Environment (JRE)? (Choose two.)

Accepted Answer

It includes the JVM. Option C is correct because the JRE bundles the Java Virtual Machine (JVM) along with the core class libraries, and the JVM is what actually executes compiled Java bytecode. Option E is correct because the JRE provides the runtime components (JVM plus standard libraries) needed to launch and run already-compiled Java applications on a machine. Option A is wrong because the JDK is the larger package, since it contains the JRE plus development tools. Option B is wrong because the Java compiler (javac) is part of the JDK, not the JRE. Option D is wrong because development tools such as javac, jar, and javadoc ship with the JDK, not the JRE.

Answer

It is larger than the JDK

Answer

It includes the Java compiler

Answer

It includes development tools

Question 10

Which THREE are benefits of Java's platform independence? (Choose three.)

Accepted Answer

Ability to run on any device with a JVM. Option A is correct because Java source is compiled to bytecode that executes on the Java Virtual Machine, so any device providing a compatible JVM can run the same class files regardless of underlying OS or CPU architecture. Option B is correct because this portability is precisely the 'write once, run anywhere' (WORA) promise: a single compiled artifact is not recompiled per platform, only interpreted/JIT-compiled by the local JVM. Option E is correct because the JVM's class loader, bytecode verifier, and SecurityManager architecture provide a sandbox that constrains untrusted code, a security benefit tied to running on the managed JVM layer. Option C is not a benefit of platform independence—bytecode is typically interpreted or JIT-compiled and generally slower to warm up than optimized native code, so it is not a portability advantage. Option D is a feature of the Java runtime (garbage collection) but is unrelated to platform independence, so it does not belong.

Answer

Faster execution compared to native code

Answer

Automatic memory management

Question 11

A developer is tasked with deploying a Java application to a customer's server. The customer has only a JRE installed and no internet access. The application uses Java NIO and requires reading configuration files from the classpath. The application compiles and runs fine on the developer's machine which has JDK 11. However, when deploying the compiled JAR to the customer's JRE 11, it throws a 'NoClassDefFoundError' for a class that is part of the JDK's internal API (e.g., com.sun.nio.file.SensitivityWatchEventModifier). The developer is confused because the class is in the standard library. Which action should be taken to resolve the issue?

Accepted Answer

Modify the code to use a public API from the standard library. The class `com.sun.nio.file.SensitivityWatchEventModifier` lives in a JDK-internal, non-exported package that is not part of the supported Java SE API and is not present in a standard JRE runtime image. The correct fix is to modify the code to use a public, supported API (for example, `java.nio.file.StandardWatchEventKinds` and `WatchService`) so the application only depends on classes guaranteed to exist in the JRE. Recompiling or adding JARs cannot make an internal JDK class available on a plain JRE.

Answer

Recompile with a lower target version

Answer

Add the missing JAR file to the classpath

Answer

Install the JDK on the customer's server

Question 12

Which THREE of the following are key features of the Java programming language?

Accepted Answer

Platform independence through bytecode and JVM. Option C is correct because Java source is compiled to platform-neutral bytecode that runs on any system with a Java Virtual Machine (JVM), which is the essence of Java's 'write once, run anywhere' design. Option D is correct because Java performs automatic memory management via garbage collection, reclaiming heap objects no longer referenced so developers don't manually free memory. Option E is correct because Java enforces strong static type checking at compile time, catching type mismatches before execution and ensuring type safety. Option A is incorrect because Java deliberately omits pointer arithmetic and direct memory access for safety, offering only references. Option B is incorrect because Java allows multiple inheritance only for interfaces, not for classes, to avoid the diamond problem.

Answer

Use of pointers for direct memory access

Answer

Support for multiple inheritance of classes

Question 13

A junior developer asks how Java achieves platform independence. Which statement best describes the role of the Java Virtual Machine (JVM) in this process?

Accepted Answer

The JVM executes Java bytecode, which is the same regardless of the underlying operating system, allowing the same compiled program to run on different platforms.. Java compiles source code to bytecode, a platform-independent intermediate representation. Each platform has a JVM that can execute that bytecode, either by interpreting it or by compiling it to native code at runtime. This architecture lets the same compiled class files run on Windows, Linux, or macOS without recompilation, which is the foundation of Java's platform independence.

Answer

The JVM provides a set of precompiled native libraries that replace the need for bytecode, so programs run as native executables.

Answer

The JVM converts Java bytecode into C source code, which is then compiled by a native compiler for the target platform.

Answer

The JVM translates Java source code directly into native machine code for the host operating system before execution.

Question 14

A university student installs the JDK on a Windows laptop and wants to compile and run a simple HelloWorld.java file from the command line without using an IDE. After compilation, which command should the student use to execute the program?

Accepted Answer

java HelloWorld. After source code is compiled with javac, the resulting bytecode is executed by the java launcher using the class name only, without the .class extension. The java command starts the JVM, locates the class on the class path, and invokes its main method. This is the fundamental compile-then-run workflow for Java SE applications.

Answer

java HelloWorld.java

Answer

run HelloWorld.class

Answer

javac HelloWorld

Question 15

A development team is choosing a Java edition for a project that must run on desktop computers and also access a central database. The application will use JavaFX for its user interface and JDBC for database connectivity. Which Java edition is the most appropriate choice?

Accepted Answer

Java SE (Standard Edition). Java SE provides the core language, the JVM, and standard libraries including JavaFX for desktop UI and JDBC for database access. Java EE is for server-side enterprise applications, Java ME targets constrained devices, and Java Card is for smart cards. The project's requirements align directly with the standard edition's feature set.

Answer

Java EE (Enterprise Edition)

Answer

Java ME (Micro Edition)

Answer

Java Card