1Z0-811 Practice Questions 2 — 50 Questions

Question 1

A developer writes the following code:

int x = 5;
switch (x) {
    case 1:
        System.out.print("One ");
    case 5:
        System.out.print("Five ");
    case 10:
        System.out.print("Ten ");
        break;
    default:
        System.out.print("Other ");
}

What is printed?

Accepted Answer

Five Ten. The switch expression x has the value 5, so execution jumps to the matching case 5 and prints "Five ". No break statement follows, so execution falls through into case 10, printing "Ten ". The break after case 10 ends the switch, so default is never reached. The result is the concatenation of both prints: Five Ten.

Answer

Five Ten Other

Answer

Five

Answer

Ten

Question 2

You are tuning a real-time data processing application that reads sensor data from a queue. The system must process each sensor reading, but occasionally a reading is invalid (null) and should be skipped. The loop must run indefinitely until the application is shut down gracefully. The current implementation uses a while(true) loop with a break condition when a shutdown flag is set. However, the loop is consuming excessive CPU because it continuously polls the queue even when no data is available. You need to modify the loop to reduce CPU usage while still processing data efficiently. Which approach should you take?

Accepted Answer

Replace the polling mechanism with a blocking queue that blocks until data is available.. Using a blocking queue (e.g., `BlockingQueue.take()`) causes the consumer thread to block automatically until data becomes available, eliminating busy-waiting and drastically reducing CPU usage. This is the standard pattern for producer-consumer scenarios in Java, as it leverages the underlying `notify`/`wait` mechanism to avoid polling overhead.

Answer

Change the while(true) loop to a for loop that iterates a fixed number of times.

Answer

Add a Thread.sleep(100) inside the loop to reduce polling frequency.

Answer

Use a do-while loop with a Thread.yield() call to give other threads CPU time.

Question 3

Given the method: public static void modify(int[] data) { data = new int[]{10,20}; } What is the output of: int[] vals = {1,2}; modify(vals); System.out.println(vals[0]);

Accepted Answer

1. In Java, when an object reference (including an array) is passed to a method, the reference itself is passed by value. Inside `modify`, the assignment `data = new int[]{10,20}` reassigns the local variable `data` to a new array object, but this does not affect the original reference `vals` in the caller. Therefore, `vals[0]` remains `1`, making option C correct.

Answer

10

Answer

Compilation error

Answer

0

Question 4

Which FOUR statements about the main method are correct? (Choose four.)

Accepted Answer

It must be declared void.. Options A, B, and C are correct because the main method must be declared void, static, and public for the JVM to invoke it as the entry point of a program. Option E is also correct: Java allows overloading of the main method; you can define multiple main methods with different parameter lists, but only the one with the standard signature `public static void main(String[] args)` is used as the program entry point. Option D is incorrect because the main method must not return a value; its return type must be void.

Answer

It must return an int.

Question 5

A developer needs to store a currency value with two decimal places. Which primitive type is most appropriate?

Accepted Answer

double. (double) is the most appropriate primitive type for storing a currency value with two decimal places because double is a 64-bit IEEE 754 floating-point type that can represent fractional values with sufficient precision for typical monetary amounts. While float (32-bit) could also store decimals, double provides higher precision (15-16 significant digits) and is the default type for decimal literals in Java, making it the standard choice for currency calculations in the exam context.

Answer

float

Answer

long

Answer

int

Question 6

A developer is reviewing code that uses assertions. Which two statements about Java assertions are true? (Choose two.)

Accepted Answer

Assertions are enabled at runtime using the -ea command-line option.. Assertions are disabled by default and must be enabled with -ea at runtime. When enabled and an assertion fails, an AssertionError is thrown. They are intended for internal invariant checks, not for validating public method parameters or handling recoverable errors, which should use exceptions.

Answer

Assertions can be used to validate parameters of public methods.

Answer

Assertions are enabled by default when running a Java application.

Answer

Assertions can be used to handle recoverable runtime errors gracefully.

Question 7

A junior developer wrote the following code to compare two strings entered by a user: if (username == "admin") { grantAccess(); } else { denyAccess(); }. The code always denies access even when the user enters 'admin'. What is the most likely cause, and how should the code be fixed?

Accepted Answer

The strings are compared using == which checks reference equality. Use username.equals("admin") instead.. In Java, the == operator compares object references, not the actual content of strings. When comparing two String objects for logical equality, the .equals() method must be used. The code if (username == "admin") checks whether username and the string literal "admin" refer to the same memory location, which is false when username is obtained from user input (e.g., via Scanner or console), even if the characters are identical.

Answer

The input string has leading or trailing spaces. Use username.trim().equals("admin") instead.

Answer

The variable username is null, causing a NullPointerException that is caught and denied access. Add a null check.

Answer

The strings are compared using == which is case-sensitive. Use username.equalsIgnoreCase("admin") instead.

Question 8

What is the output of the following code?

int i = 0;
while (i < 5) {
    if (i == 3) {
        i++;
        continue;
    }
    System.out.print(i + " ");
    i++;
}

Accepted Answer

0 1 2 4. The while loop iterates while i < 5. When i equals 3, the if condition triggers, incrementing i to 4 and then using continue to skip the print statement for that iteration. Thus, 3 is never printed, and the loop prints 0, 1, 2, and then 4 before i becomes 5 and the loop ends.

Answer

0 1 2 3

Answer

0 1 2 4 5

Answer

0 1 2 3 4

Question 9

A developer writes a method that takes a variable number of integer arguments and returns the maximum. Which method signature is correct?

Accepted Answer

public int max(int... numbers). The varargs syntax `int... numbers` allows a method to accept zero or more integer arguments, which are then treated as an array inside the method. This is the standard Java syntax for variable-length argument lists, enabling the developer to pass any number of `int` values and compute the maximum.

Answer

public int max(int[]... numbers)

Answer

public int max(int numbers)

Answer

public int max(int[] numbers)

Question 10

In a nested loop structure, a developer wants to exit completely from the outer loop when a certain condition is met inside the inner loop. Which approach is correct?

Accepted Answer

Use a labeled break statement (e.g., break outerLabel;).. Java's labeled break statement allows a developer to specify an outer loop label and break out of that loop entirely from within an inner loop. This is the only control flow mechanism designed to exit multiple nested loops at once, as a plain break only exits the innermost loop.

Answer

Use a return statement within the inner loop.

Answer

Use a continue statement with a label.

Answer

Use a break statement inside the inner loop.

Question 11

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 12

A developer needs to iterate over an array of integers and compute the sum of its elements. Which loop construct is most appropriate for this task?

Accepted Answer

Enhanced for loop. The enhanced for loop (for-each) is the most appropriate construct for iterating over an array of integers to compute a sum because it provides a concise, read-only traversal without needing an explicit index or iterator. It directly accesses each element in sequence, reducing boilerplate and the risk of off-by-one errors, which is ideal for aggregation operations like summation.

Answer

while loop

Answer

switch statement

Answer

do-while loop

Question 13

Given the code:

int[] a = {1, 2, 3};
int[] b = {4, 5};
a = b;
b[0] = 99;
System.out.println(a[0]);

What is the output?

Accepted Answer

99. After `a = b;`, both `a` and `b` reference the same array object. Modifying `b[0]` to 99 also changes `a[0]` because they share the same underlying array. Therefore, `a[0]` prints 99.

Answer

3

Answer

1

Answer

4

Question 14

What is the value of the expression: 2 + 3 * 4 / 2 - 1?

Accepted Answer

7. In Java, the expression 2 + 3 * 4 / 2 - 1 is evaluated according to operator precedence: multiplication (*) and division (/) have higher precedence than addition (+) and subtraction (-), and they associate left-to-right. So 3 * 4 = 12, then 12 / 2 = 6 (integer division). The expression becomes 2 + 6 - 1, which is evaluated left-to-right: 2 + 6 = 8, then 8 - 1 = 7. Thus the correct answer is 7.

Answer

9

Answer

10

Answer

3

Question 15

In a banking application, a class 'Account' has a private field 'balance'. Which is the best way to allow subclasses to read but not directly modify 'balance'?

Accepted Answer

Provide a public getBalance() method. It follows encapsulation: a public getBalance() method provides read-only access to the private balance field. Subclasses cannot directly modify balance because it is private. Option D (protected) is incorrect because protected access allows subclasses to directly read and write the field, which violates the requirement that subclasses should not be able to directly modify balance.

Answer

Make balance public

Answer

Use a static variable

Answer

Make balance protected

Question 16

Arrange the steps to use a for loop to iterate over an array in Java in the correct order.

Accepted Answer

1. Declare and initialize the array. 2. Write a for loop with initialization, condition, and increment statements. 3. Access elements using array[index] inside the loop. 4. Execute desired operations on each element.. First set up the array, then write a for loop with proper syntax, access elements using index, execute body, and consider enhanced for.

Answer

1. Write a for loop header with initialization, condition, and increment. 2. Declare and initialize the array inside the loop. 3. Access elements using array[index]. 4. Perform operations.

Answer

1. Access array elements using index. 2. Declare and initialize the array. 3. Write a for loop to iterate. 4. Perform operations.

Answer

1. Declare and initialize the array. 2. Perform operations on array elements without a loop. 3. Write a for loop later. 4. Access elements using index.

Question 17

A developer implements a method to check if a number exists in an array using binary search. The array is not sorted. What will happen?

Accepted Answer

The method returns incorrect results sometimes.. Binary search requires the array to be sorted to work correctly. If the array is not sorted, the algorithm may skip over the target element or incorrectly conclude it is absent, leading to incorrect results. Therefore, the method returns incorrect results sometimes.

Answer

The method returns correct results always.

Answer

Runtime exception.

Answer

Compilation error.

Question 18

Which THREE statements about custom exceptions in Java are correct? (Select exactly 3)

Accepted Answer

A checked custom exception must be declared in the throws clause of any method that throws it.. Option A is correct because a checked exception (any subclass of Exception that is not a subclass of RuntimeException) is subject to the Java checked-exception rule, so any method that throws it must declare it in its throws clause or the code will not compile. Option B is correct because a custom exception can be designed as either checked (extending Exception) or unchecked (extending RuntimeException), giving the developer control over whether callers are forced to handle it. Option C is correct because the defining characteristic of an unchecked exception in Java is that it extends RuntimeException (or one of its subclasses), so an unchecked custom exception must extend RuntimeException. Option D is incorrect because a custom exception need not extend Throwable directly; it typically extends Exception or RuntimeException, which already inherit from Throwable. Option E is incorrect because custom exceptions can and commonly do define constructors that call super(...) to pass messages or causes to the parent class.

Answer

A custom exception class must directly extend Throwable.

Answer

A custom exception cannot have constructors that call super.

Question 19

A developer is debugging a Java application that throws a NullPointerException. Which two actions help identify the source of the exception? (Choose two.)

Accepted Answer

Use a debugger to step through code. Option B is correct because a debugger lets you set breakpoints and step through the code line by line, inspecting variable values and the call stack at the exact moment the NullPointerException is thrown, which pinpoints the null reference. Option C is correct because the stack trace printed when a NullPointerException is thrown shows the exact class, method, file, and line number where the null dereference occurred, immediately identifying the source. Option A is not ideal because println statements only show whatever you explicitly print and do not reveal the exception's origin or call path. Option D is wrong because the -g flag only adds debugging symbols (line numbers, local variable info) to the compiled class files; it does not itself identify where the exception came from. Option E is insufficient because catching the exception and printing only its message typically yields just 'null' without the stack trace, so the source location remains unknown.

Answer

Use System.out.println statements

Answer

Recompile with -g flag

Answer

Catch the exception and print its message

Question 20

Given: String s = "Java"; s.concat(" Rocks"); System.out.println(s); What prints?

Accepted Answer

"Java". Strings in Java are immutable. The `concat()` method returns a new string object but does not modify the original string `s`. Since the return value is not assigned to any variable, the original string `s` remains unchanged, so `System.out.println(s)` prints "Java".

Answer

"Rocks"

Answer

""

Answer

"Java Rocks"