1Z0-811 Practice Test 21 — 15 Questions

Question 1

What likely caused this compilation error?

Accepted Answer

The filename does not match the public class name. The compilation error occurs because Java requires that the public class name exactly matches the filename (including case) when the class is declared as public. If the filename is different from the public class name, the compiler will fail with an error indicating the class name is incorrect or cannot be found.

Answer

The main method is missing

Answer

The file is saved with a .txt extension instead of .java

Answer

The class name contains a typo

Question 2

Consider a method that takes an int array and modifies it: public static void doubleArray(int[] arr) { for (int i = 0; i < arr.length; i++) { arr[i] *= 2; } }. What is the output of: int[] nums = {1, 2, 3}; doubleArray(nums); System.out.println(nums[1]);

Accepted Answer

4. The method `doubleArray` multiplies each element of the array by 2. The array `nums` is passed by reference, so modifications inside the method affect the original array. After execution, `nums[1]` (originally 2) becomes 4, which is printed.

Answer

8

Answer

2

Answer

3

Question 3

What is the primary purpose of Java bytecode?

Accepted Answer

To be executed by the Java Virtual Machine on any platform. Java bytecode is designed to be executed by the Java Virtual Machine (JVM), which interprets or compiles it to native code for the underlying platform, enabling platform independence. Option B is incorrect because bytecode is an intermediate representation that is compiled or interpreted at runtime, not compiled once into native code for reuse across platforms. Option C is incorrect because bytecode is not human-readable source code; it is a binary format. Option D is incorrect because bytecode cannot be directly executed by the operating system; it requires the JVM to run.

Answer

To be compiled into native code once and reused

Answer

To be human-readable source code

Answer

To be directly executed by the operating system

Question 4

A method is expected to receive an integer and return its square. Which method signature is correct?

Accepted Answer

int square(int x) { return x*x; }. The method signature specifies a return type of 'int' and includes the 'return' keyword to return the squared value. In Java, a method that returns a value must declare the return type before the method name and must use the 'return' statement to send the result back to the caller.

Answer

void square(int x) { return x*x; }

Answer

public square(int x) { return x*x; }

Answer

int square(int x) { x*x; }

Question 5

What is the value of sum printed?

int sum = 0;
for (int i = 0; i < 3; i++) {
    sum = sum + i;
}
System.out.println(sum);

Accepted Answer

3. The loop initializes sum to 0 and iterates i from 0 to 2 inclusive. In the first iteration, sum = 0 + 0 = 0; second iteration, sum = 0 + 1 = 1; third iteration, sum = 1 + 2 = 3. After the loop, sum is printed, so the output is 3. Option C is correct.

Answer

6

Answer

0

Answer

1

Question 6

Which TWO statements are true about passing arrays to methods in Java?

Accepted Answer

The method can modify the elements of the array.. Option B is correct because Java passes the array's reference by value, so the method receives a reference that points to the same underlying array object; any assignment to an element such as arr[0] = 5 is therefore visible to the caller. Option D is correct because Java is strictly pass-by-value, and for arrays the value being passed is a copy of the reference (the memory address) to the array object, not a copy of the array's contents. Option A is incorrect because reassigning the parameter (e.g., arr = new int[5]) only changes the local copy of the reference and does not affect the caller's original array variable. Option C is incorrect because changes to array elements are reflected without returning the array, since both references point to the same object. Option E is incorrect because a method can always determine the array's length via the array's length field (e.g., arr.length).

Answer

The method can reassign the original array variable to a new array.

Answer

The method must return the array to reflect any changes.

Answer

The method cannot determine the size of the array.

Question 7

Arrange the steps to compile and run a Java program from the command line in the correct order.

Accepted Answer

Write code, Open terminal, Navigate to file directory, Compile with javac, Run with java. The correct order is to first write the code, then open terminal, navigate to the file location, compile with javac, and run with java.

Answer

Write code, Open terminal, Compile with javac, Navigate to file directory, Run with java

Answer

Open terminal, Write code, Navigate to file directory, Compile with javac, Run with java

Answer

Write code, Open terminal, Navigate to file directory, Run with java, Compile with javac

Question 8

Which approach does NOT create a new array that is independent of the original?

Accepted Answer

int[] copy = original;. `int[] copy = original;` simply assigns the reference of the existing array to a new variable. No new array object is created; both `copy` and `original` point to the same array in memory. Therefore, modifying `copy[0]` also changes `original[0]`, so the array is not independent.

Answer

int[] copy = Arrays.copyOf(original, original.length);

Answer

int[] copy = original.clone();

Answer

int[] copy = new int[original.length]; System.arraycopy(original, 0, copy, 0, original.length);

Question 9

Which TWO statements are true about the finally block in exception handling? (Select exactly 2)

Accepted Answer

The finally block is executed even if the try block contains a return statement.. Option D is correct because the finally block is guaranteed to run even when the try block executes a return statement; the JVM evaluates the return value, then runs the finally block before actually returning (and a return inside finally would override it). Option E is correct because the finally block executes after the try block and after any catch block that handled an exception, but before control returns to the caller, ensuring cleanup code runs on all exit paths. Option A is wrong because finally runs whether or not an exception is thrown, not only when one occurs. Option B is wrong because omitting finally is unrelated to checked exceptions; a try can legally have only a finally (no catch), and try-with-resources or catch blocks handle checked exceptions independently. Option C is wrong because finally also executes when an exception is thrown and caught, or propagates, not only when no exception occurs.

Answer

The finally block is executed only if an exception is thrown.

Answer

The finally block can be omitted only if the try block does not throw any checked exception.

Answer

The finally block is executed only if no exception is thrown.

Question 10

A developer writes a class 'Vehicle' with a method 'move()' that prints 'Vehicle moves'. A subclass 'Car' overrides 'move()' to print 'Car moves'. Given: Vehicle v = new Car(); v.move(); What is the output?

Accepted Answer

Car moves. Java uses dynamic method dispatch (runtime polymorphism). Even though the reference variable is of type 'Vehicle', the actual object is a 'Car' instance. At runtime, the JVM calls the overridden 'move()' method of the 'Car' class, printing 'Car moves'.

Answer

Vehicle moves

Answer

Runtime exception

Answer

Compilation fails

Question 11

A junior developer writes a method that attempts to modify a String: public void update() { String s = "Hello"; s.concat(" World"); System.out.println(s); } What will be printed when update() is called?

Accepted Answer

Hello. String objects in Java are immutable, so calling s.concat(" World") returns a new String rather than modifying s. Because the return value is discarded and s is never reassigned, s still references the original "Hello" literal, so System.out.println(s) prints Hello.

Answer

Hello World

Answer

Hello World (no space)

Answer

Compilation error

Question 12

A method 'public static double average(int[] numbers) { int sum = 0; for (int i = 0; i < numbers.length; i++) sum += numbers[i]; return sum / numbers.length; }' is called with array {10, 20, 30}. What change is needed to return the correct average?

Accepted Answer

Change 'sum / numbers.length' to '(double) sum / numbers.length'. The method performs integer division because both `sum` (int) and `numbers.length` (int) are integers, truncating the fractional part. Casting `sum` to `double` before division forces floating-point arithmetic, preserving the decimal value. For the array {10, 20, 30}, the correct average is 20.0, but integer division yields 20 (truncated from 20.0, though here it matches by coincidence; for non-integer averages like {10, 20, 31}, the error would be obvious).

Answer

Change the loop to for (int i = 1; i <= numbers.length; i++)

Answer

Change return type to int

Answer

Add a second parameter for the length

Question 13

Which TWO statements correctly describe the Java language? (Choose two.)

Accepted Answer

Java supports object-oriented programming.. Java is fundamentally an object-oriented programming language that supports encapsulation, inheritance, and polymorphism. Java's design revolves around classes and objects, and all code must be written inside a class, making OOP a core principle of the language.

Answer

Java supports multiple inheritance of implementation.

Answer

Java supports operator overloading.

Answer

Java supports multiple inheritance of classes.

Question 14

Given a method that catches Exception and then throws a RuntimeException, what is the effect?

Accepted Answer

The method can throw RuntimeException without declaring it.. In Java, RuntimeException is an unchecked exception, meaning it does not need to be declared in a method's throws clause. The catch block catches Exception (which includes RuntimeException), and then throws a new RuntimeException. Since RuntimeException is unchecked, the method can throw it without declaring it, making option B correct.

Answer

The RuntimeException will not propagate if caught.

Answer

The method must declare throws RuntimeException.

Answer

The catch block cannot throw a RuntimeException because it is caught as Exception.

Question 15

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