1Z0-811 Practice Test 32 — 15 Questions

Question 1

A class 'Base' has a method 'public void display() throws IOException'. Subclass 'Derived' overrides display(). Which exception specifications are allowed in the overriding method?

Accepted Answer

public void display() throws FileNotFoundException. In Java, an overriding method can throw the same exception, a subclass of the exception thrown by the parent method, or no exception at all. The parent method throws IOException, so the overriding method may throw FileNotFoundException (a subclass of IOException). This follows the rule that the overriding method cannot throw a broader checked exception than the overridden method.

Answer

public void display() throws SQLException

Answer

public void display() throws Exception

Answer

public void display() throws Throwable

Question 2

Given the following code,

String s1 = new String("example");
String s2 = "example";
System.out.println(s1 == s2);

Why does the code output false?

Accepted Answer

s1 is created with 'new' thus not in string pool, s2 is literal in pool, so different references. The code likely creates s1 using the 'new' operator, which forces the creation of a new String object in the heap, not in the string pool. s2 is a string literal, which is interned and placed in the string pool. The '==' operator compares object references, so s1 and s2 refer to different objects, hence the comparison returns false.

Answer

s1 and s2 refer to different objects in the heap

Answer

The String class does not override equals

Answer

The == operator compares value not reference

Question 3

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 4

A financial trading application processes a batch of 10 million trade transactions every night. Each transaction is a String containing trade details such as ID, symbol, quantity, and price. The current implementation uses string concatenation with the += operator in a loop to build a summary report string. The application frequently runs out of memory and takes hours to complete. The server has 16 GB of RAM and runs Java 11. The code cannot be restructured significantly due to regulatory requirements, but performance improvements are allowed. Which course of action will most effectively resolve the performance and memory issues?

Accepted Answer

Replace the String concatenation with StringBuilder.. The performance and memory issues are caused by using String concatenation (+=) inside a loop, which creates many intermediate String objects because Strings are immutable in Java. StringBuilder is mutable and designed for efficient string concatenation without creating intermediate objects, making it the optimal solution. Option A (StringBuilder) is correct. Option B (calling intern()) would not improve performance and could degrade it. Option C (increasing heap size) only postpones the OutOfMemoryError and does not fix the inefficiency. Option D (StringBuffer) is thread-safe but slower due to synchronization; it is unnecessary in this single-threaded context. Therefore, replacing concatenation with StringBuilder is the most effective resolution.

Answer

Call intern() on the concatenated result at each iteration.

Answer

Increase the JVM heap size to 32 GB to accommodate the temporary string objects.

Answer

Replace the String concatenation with StringBuffer.

Question 5

Which TWO are valid identifiers in Java? (Choose two.)

Accepted Answer

$money. In Java, identifiers can begin with a letter, an underscore (_), or a dollar sign ($). The dollar sign is a valid starting character, so '$money' is a legal identifier. This is specified in the Java Language Specification (JLS §3.8).

Answer

123abc

Answer

2ndPlace

Answer

my-var

Question 6

Given the following try-catch block:
try {
    // some code
} catch (IOException | NumberFormatException e) {
    e = new IOException("wrapper");
    // throw e;
}
Which line causes a compilation error?

Accepted Answer

The assignment to e. In a multi-catch block, the exception parameter `e` is implicitly `final` and cannot be reassigned. The assignment `e = new IOException("wrapper")` violates this rule, causing a compilation error at that line.

Answer

The multi-catch syntax

Answer

No error

Answer

The throw statement

Question 7

What is the result of the following code snippet? int x = 5; int y = 2; double z = x / y; System.out.println(z);

Accepted Answer

2.0. In Java, when both operands of the division operator are integers (int), the operation performs integer division, which truncates the fractional part. Here, x / y = 5 / 2 = 2 (integer division), and then the result is implicitly widened to double when assigned to z, producing 2.0.

Answer

3.0

Answer

2

Answer

2.5

Question 8

A developer wants to assign the largest possible long value to a variable. Which is correct?

Accepted Answer

long x = Long.MAX_VALUE;. The correct answer is E. Long.MAX_VALUE is the standard and readable way to obtain the maximum long value. While option D (9223372036854775807L) is syntactically valid, it is not recommended because it is error-prone and does not clearly convey intent. Options A and C are incorrect: A has an unnecessary cast, and C omits the L suffix, causing a compile error. Option B exceeds the long range.

Answer

long x = (long) 9223372036854775807L;

Answer

long x = 9223372036854775808L;

Answer

long x = 9223372036854775807;

Answer

long x = 9223372036854775807L;

Answer

long x = (long) 1e19;

Answer

long x = 9223372036854775807;

Question 9

You are a junior developer tasked with generating API documentation for a large Java project. The project uses Javadoc comments extensively, and you need to generate HTML documentation that includes all public and protected classes and methods. You have access to the source files in the `src` directory, and you want the output to be placed in a `docs` folder. Additionally, you want to include a custom header and footer in each generated page. The project uses multiple packages like `com.example.app`, `com.example.util`, and `com.example.data`. You plan to run the javadoc command from the project root. Which command should you use?

Accepted Answer

javadoc -d docs -header 'My App API' -footer 'Copyright 2024' -sourcepath src com.example.app com.example.util com.example.data. It specifies the exact package names (`com.example.app`, `com.example.util`, `com.example.data`) that contain the public and protected classes and methods required for the documentation, uses `-d docs` to set the output directory, and includes `-header` and `-footer` to add custom header and footer text. This command generates HTML documentation for only the specified packages, meeting all requirements.

Answer

Answer

javadoc -d docs -private -sourcepath src com.example.app com.example.util com.example.data

Answer

Question 10

What is printed when the main method runs?

Accepted Answer

5. The method `modifyArray` receives a reference to the array, and the assignment `arr = new int[]{100};` changes the local reference `arr` to point to a new array object. The original array in `main` remains unchanged, so `arr[0]` still prints 5. Java passes object references by value, meaning the reference itself is copied, and reassigning the local reference does not affect the caller's reference.

Answer

0

Answer

Compilation error: cannot assign new array to parameter

Answer

100

Question 11

A developer implements a loop that processes a list of transactions. The loop must ensure that at least one transaction is processed even if the list is empty. Which loop construct guarantees this?

Accepted Answer

do-while loop. The do-while loop is the correct choice because it guarantees that the loop body executes at least once, regardless of the condition. In Java, the do-while loop evaluates its boolean condition after executing the loop body, so even if the list is empty (e.g., size 0), the transaction processing code inside the loop will run once before the condition is checked.

Answer

while loop

Answer

enhanced for loop

Answer

for loop

Question 12

Refer to the exhibit. What is the output?

Accepted Answer

12. The exhibit shows code that initializes an integer array with values 1 through 5. The enhanced for loop iterates over each element, adding each value to the variable 'sum' (starting at 0). After summing all five elements (1+2+3+4+5), sum equals 15. The code then prints the value of sum minus 3, which is 12. Therefore, option C is correct.

Answer

10

Answer

13

Answer

11

Question 13

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 14

A developer wants to prevent a method from being overridden. Which modifier should be used?

Accepted Answer

final. The `final` modifier prevents a method from being overridden in a subclass. When a method is declared as `final`, any attempt to override it in a subclass results in a compile-time error, ensuring the method's implementation remains unchanged.

Answer

private

Answer

abstract

Answer

static

Question 15

A method that calculates the average of an array of doubles is defined as:

public static double average(double[] values) {
    double sum = 0;
    for (double v : values) sum += v;
    return sum / values.length;
}

Which call is valid?

Accepted Answer

double avg = average(new double[]{1.0, 2.0, 3.0});. The method `average(double[] values)` expects a single argument of type `double[]`. The expression `new double[]{1.0, 2.0, 3.0}` creates an anonymous array object that matches the parameter type exactly, so the call compiles and runs correctly.

Answer

double avg = average(1.0, 2.0);

Answer

double avg = average(1.0, 2.0, 3.0);

Answer

double avg = average({1.0, 2.0, 3.0});