1Z0-811 Practice Test 33 — 15 Questions

Question 1

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 2

A developer writes a class Logger with a private static Logger instance and a public static Logger getInstance() method. The method checks if instance is null and creates it. Two threads call getInstance() simultaneously on first use. What is the most likely problem?

Accepted Answer

Two Logger objects may be created because the null check and assignment are not atomic.. Lazy initialization without synchronization allows a race condition. Two threads can both observe instance as null, both create a Logger, and both assign it, producing multiple instances. Synchronizing getInstance(), using a static holder class, or using an enum-based singleton prevents the race and preserves the single-instance guarantee.

Answer

A compile-time error occurs because static methods cannot access private static fields.

Answer

The JVM throws an IllegalStateException because static initialization is not thread-safe.

Answer

A NullPointerException is thrown because instance is not initialized before getInstance() is called.

Question 3

A logistics company stores shipment weights in a Java program. A developer writes the following statement: int weight = 15.75; What is the result when this line is compiled?

Accepted Answer

Compilation fails because a double literal cannot be assigned to an int variable without an explicit cast.. Assigning a double literal to an int variable is a narrowing primitive conversion, which Java permits only with an explicit cast. The compiler enforces this to prevent silent loss of the fractional part. Because the statement lacks a cast, compilation fails before any value is stored. This highlights Java's strict type-safety rules for primitive assignments.

Answer

The program compiles and weight is assigned the value 16 because the value is rounded.

Answer

The program compiles and weight becomes a double variable automatically.

Answer

The program compiles and weight is assigned the value 15 after truncation.

Question 4

A programmer writes the following code:

public class Test {
    public static void main(String[] args) {
        int i = 0;
        for (; i < 3; i++) {
            System.out.print(i + " ");
        }
    }
}

What is the output?

Accepted Answer

0 1 2. The for loop header allows the initialization section to be empty. Since i is declared and set to 0 before the loop, the loop uses that existing variable. The condition i < 3 is evaluated before each iteration, and the update i++ runs after each iteration. The values printed are 0, 1, and 2, each followed by a space. When i reaches 3, the condition fails, and the loop terminates.

Answer

0 1 2 3

Answer

Compilation fails because the initialization part of the for loop is missing.

Answer

1 2 3

Question 5

A developer is writing a Java class and needs to declare local variables that follow valid Java naming and declaration rules. Which two of the following declarations are valid and will compile without error? (Choose two.)

Accepted Answer

int maxValue = 100;. Legal Java identifiers must begin with a letter, an underscore, or a currency symbol and may continue with those characters plus digits, and they may not be keywords or the reserved literal names. The underscore-prefixed name and the camelCase name both satisfy these rules, while the digit-leading name, the hyphenated name, and the keyword name each violate a distinct restriction and fail to compile.

Answer

int 2ndPlace = 2;

Answer

int class = 3;

Answer

int total-count = 5;

Question 6

A developer needs to iterate over an array of department names and print each one. The array may contain null entries, and the code must handle a null entry by printing the text "unknown" instead of causing a NullPointerException. Which loop construct is most appropriate for iterating over the array while still allowing a null check before each element is used?

Accepted Answer

A traditional for loop with an index, checking each element for null before use.. A traditional for loop with an index lets the code examine each array slot directly, so a null check can be applied before printing. The enhanced for loop would still throw a NullPointerException if a method is called on a null element without a guard, and the other loop forms introduce incorrect execution order or assumptions about array contents.

Answer

A do-while loop that assumes the array is non-empty and accesses elements without bounds checking.

Answer

A while loop that increments the index before checking the array length.

Answer

An enhanced for loop (for-each) that directly calls a method on each element without checking for null.

Question 7

A developer is explaining the key characteristics of the Java programming language to a colleague. Which two statements accurately describe Java? (Choose two.)

Accepted Answer

Java programs automatically manage memory through garbage collection.. Java is object-oriented, supporting encapsulation, inheritance, and polymorphism. It also features automatic garbage collection, which manages memory without explicit developer intervention. These two characteristics are fundamental to Java's design. The other statements are incorrect because Java compiles to bytecode, does not support multiple inheritance of classes, and does not expose pointers for direct memory access.

Answer

Java allows multiple inheritance of classes to promote code reuse.

Answer

Java requires explicit pointer manipulation for dynamic memory access.

Answer

Java source code is compiled directly to native machine code for the target platform.

Question 8

A developer writes the following method to classify a character:

public static String classify(char c) {
    switch (c) {
        case 'a':
        case 'e':
        case 'i':
        case 'o':
        case 'u':
            return "vowel";
        case 'y':
            return "sometimes";
        default:
            return "consonant";
    }
}

What is printed by System.out.println(classify('e'));?

Accepted Answer

vowel. The character 'e' matches its case label, and because the vowel labels are stacked with no statements between them, control falls through to the shared return. The method returns the string "vowel". Stacking labels is a standard Java idiom for mapping several input values to one outcome.

Answer

sometimes

Answer

consonant

Answer

Compilation fails because stacked case labels without break statements are illegal.

Question 9

A developer writes the following code: int x = 7; int y = 2; double result = x / y; System.out.println(result); What is printed, and why?

Accepted Answer

3.0, because x / y performs integer division and the int result is widened to double on assignment.. Operator evaluation happens left to right, and the type of each operand drives which division is performed. Because x and y are both int, the / operator carries out integer division, discarding the remainder and yielding 3. Only afterward is that int widened to 3.0 for storage in the double variable, so the printed value is 3.0.

Answer

3.5, because result is a double and the assignment promotes the division to floating-point.

Answer

3, because result is printed before any widening occurs.

Answer

An ArithmeticException is thrown because 7 is not evenly divisible by 2.

Question 10

A class Vehicle has a constructor that takes an int parameter. A subclass Car has a constructor that takes an int parameter and needs to initialize the inherited part using the Vehicle constructor. Which statement about constructor chaining is correct?

Accepted Answer

The Car constructor must call super(value) as its first statement to invoke the Vehicle constructor.. Constructor chaining requires that a subclass constructor invoke an accessible superclass constructor. When the superclass has no no-arg constructor, the subclass must explicitly call super(...) with matching arguments as the first statement. Relying on the implicit super() call fails, and this(...) only delegates within the same class.

Answer

The Car constructor can call this(value) instead of super(value) to initialize the Vehicle part.

Answer

The Car constructor automatically calls the Vehicle(int) constructor without any explicit code.

Answer

The Car constructor can call super(value) anywhere in its body as long as it is before field assignments.

Question 11

A developer writes a class `Counter` with a private static int field `count` and an instance method `increment()` that performs `count++`. The developer creates three separate Counter objects and calls `increment()` on each one once. What is the value of count after all three calls?

Accepted Answer

3, because all three objects share the single static field count.. A static field is created once per class and shared across all instances. Even though increment() is an instance method, the count++ it performs targets the single class-level variable, so three calls across three objects produce a value of three. The distinction between class-level and instance-level state is the central concept being exercised.

Answer

1, because each object maintains its own copy of count.

Answer

0, because static fields are reset whenever a new object is constructed.

Answer

It cannot be determined because static field access through an instance reference is a compile-time error.

Question 12

A junior developer writes the following code snippet:

int x = 10;
if (x = 5) {
    System.out.println("Equal");
} else {
    System.out.println("Not Equal");
}

What happens when this code is compiled and run?

Accepted Answer

The code causes a compile-time error because the condition must be a boolean expression.. The if statement in Java requires a boolean expression. The expression x = 5 is an assignment that produces an int value, not a boolean, so the compiler rejects the code with a type mismatch error. Using the equality operator == would compare x with 5 and yield a boolean, which is the correct approach for a condition. The assignment operator cannot be used where a boolean is expected.

Answer

The code causes a runtime exception because x is assigned a new value.

Answer

The code compiles and prints "Equal".

Answer

The code compiles and prints "Not Equal".

Question 13

A developer defines a class with two methods: public void log(String message) and public void log(String message, int level). A call site uses log("Ready"). Which statement best describes what happens at compile time and runtime?

Accepted Answer

The compiler selects log(String) based on the number of arguments, and the call binds to that method.. Overloading is resolved at compile time by matching the argument count and types to the most specific applicable method. A call with one String argument matches only log(String), so the compiler binds that method. The other overload requires an additional int argument and is not a candidate. No default values or runtime selection are involved.

Answer

The compiler reports an error because the method names are the same and the parameter lists differ only by an extra int.

Answer

The call is ambiguous, and the compiler requires an explicit cast to resolve between the two log methods.

Answer

The runtime chooses log(String, int) and supplies a default level of 0 because the int parameter is optional.

Question 14

A developer writes the following code in a Java application:

String s = "Hello";
s.concat(" World");
System.out.println(s);

What is printed?

Accepted Answer

Hello. Strings in Java are immutable. The concat method returns a new String rather than modifying the original. Because the return value is not assigned, the variable s continues to reference the original "Hello" string, so Hello is printed. The key is recognizing that String methods never change the existing object.

Answer

A compile-time error occurs.

Answer

World

Answer

Hello World

Question 15

A junior developer is reviewing a Java source file and sees the following declaration at the top of the file:

package com.acme.util;

Which statement correctly describes the requirement for this declaration?

Accepted Answer

It must be the first statement in the file, before any import statements.. The package declaration, when used, must be the first line of a Java source file, preceding all import statements and type declarations. It applies to every class or interface defined in that file. Placing imports before the package line, or repeating the package line, produces compilation errors, making the first-statement requirement the defining rule.

Answer

It is optional and can be placed anywhere in the file as long as it is unique.

Answer

It must be repeated in every class declared inside the same source file.

Answer

It may appear after import statements but before the first class declaration.