1Z0-811 Practice Test 26 — 15 Questions

Question 1

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.. Option B is correct because 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 2

A development team is building a library management system. The system has classes 'LibraryItem', 'Book', and 'DVD'. LibraryItem has a method 'getTitle()' that returns the title. Book and DVD extend LibraryItem. The team wants to ensure that when a LibraryItem is borrowed, a message specific to its type is displayed. They have a 'Borrower' class with a method 'borrow(LibraryItem item)', which currently calls 'item.getTitle()' and prints the title. Now they need to display 'Book borrowed' or 'DVD borrowed' based on the actual item type. They want to avoid using 'instanceof' checks in the 'borrow' method to keep it open for new item types. Which design should they use?

Accepted Answer

Define an abstract method 'getBorrowMessage()' in LibraryItem, and implement it in Book and DVD. Call that method in borrow().. Option C is correct because it applies the Open/Closed Principle: LibraryItem defines an abstract getBorrowMessage() method, and each subclass provides its own implementation. The borrow() method calls this polymorphic method without needing instanceof or type checks, so adding new item types (e.g., Magazine) only requires implementing getBorrowMessage() in the new subclass without modifying existing code.

Answer

Add a String field 'type' to LibraryItem and set it in each subclass constructor. In borrow(), check the field.

Answer

Use a switch statement on the class name in borrow().

Answer

Override the 'borrow' method in each subclass and call a different method.

Question 3

Which TWO are valid ways to handle a checked exception in a method?

Accepted Answer

Catch the exception within the method. Option A is correct because catching a checked exception within the method using a try-catch block is a valid way to handle it. The Java compiler enforces that checked exceptions (subclasses of Exception but not RuntimeException) must be either caught or declared, so catching the exception satisfies the compiler's requirement.

Answer

Ignore the exception by doing nothing

Answer

Use assert to suppress the exception

Answer

Convert it to a runtime exception by throwing a new RuntimeException

Question 4

Which of the following exceptions is a checked exception?

Accepted Answer

IOException. Option C is correct because IOException is a checked exception in Java, meaning it must be either caught or declared in the method signature using a try-catch block or throws clause. Checked exceptions are subclasses of Exception (excluding RuntimeException and its subclasses), and IOException directly extends Exception, making it subject to compile-time checking.

Answer

ArrayIndexOutOfBoundsException

Answer

ArithmeticException

Answer

NullPointerException

Question 5

A developer writes: char c = 'A'; int i = c + 1; System.out.println(i); What is the output?

Accepted Answer

66. In Java, when a `char` is involved in arithmetic with an `int`, the `char` is promoted to its Unicode/ASCII numeric value. 'A' has the ASCII value 65, so `c + 1` becomes 66. The result is an `int`, and `System.out.println(i)` prints the integer 66.

Answer

B

Answer

Compilation error: cannot add char and int.

Answer

'A1'

Question 6

Which command compiles a Java file and generates a .class file?

Accepted Answer

javac. The `javac` command is the Java compiler, which translates Java source code (`.java` files) into bytecode stored in `.class` files. This is the standard compilation step in the Java development process, as defined by the Java SE specification.

Answer

jar

Answer

javadoc

Answer

java

Question 7

A custom exception class must extend which class to be a checked exception?

Accepted Answer

Exception. Option D is correct because, in Java, a checked exception is any exception that is a subclass of `Exception` but not a subclass of `RuntimeException`. To create a custom checked exception, your class must extend `Exception` (or a subclass of `Exception` that is itself a checked exception). This forces callers to handle or declare the exception, enforcing compile-time checking.

Answer

Throwable

Answer

Error

Answer

RuntimeException

Question 8

What does the java command with -jar option do?

Accepted Answer

Executes a JAR file by reading its manifest. The `java -jar` command executes a JAR file by reading the `Main-Class` entry from the JAR's manifest file (`META-INF/MANIFEST.MF`). This tells the Java launcher which class contains the `public static void main(String[] args)` method to start the application. It does not compile, list, or create JAR files.

Answer

Compiles Java files inside the JAR

Answer

Lists contents of the JAR file

Answer

Creates a new JAR file

Question 9

Refer to the exhibit. What is the result?

Accepted Answer

Runtime exception. The code attempts to divide an integer by zero, which in Java throws an ArithmeticException at runtime. Since the division is performed with integer operands (int / int), Java does not allow division by zero and raises an exception, not a floating-point infinity or zero. Therefore, the correct answer is C: Runtime exception.

Answer

Compilation error

Answer

0

Answer

Infinity

Question 10

Which of the following is NOT a primitive data type?

Accepted Answer

String. String is a class in Java, not a primitive data type. The eight primitive types are byte, short, int, long, float, double, boolean, and char. String is a reference type that stores a sequence of characters as an object.

Answer

int

Answer

boolean

Answer

char

Question 11

Which two of the following are primitive data types in Java? (Choose two)

Accepted Answer

boolean. Option A is correct because `boolean` is a primitive data type in Java that can hold only two values: `true` or `false`. It is not an object and does not have methods, making it a fundamental building block for conditional logic.

Answer

Character

Answer

String

Answer

Integer

Question 12

Which THREE of the following are primitive data types in Java?

Accepted Answer

double. Option B is correct because `double` is one of the eight primitive data types in Java, used to store floating-point numbers with double precision (64-bit IEEE 754). It is a fundamental type that holds a numeric value directly, not an object reference.

Answer

String

Answer

array

Question 13

Consider the following code snippet: 
public int getValue() {
    try {
        return 1;
    } catch (Exception e) {
        return 2;
    } finally {
        return 3;
    }
}
What does the method return?

Accepted Answer

3. The correct answer is A (3) because a `finally` block always executes after the `try` block, and if the `finally` block contains a `return` statement, that return value overrides any return value from the `try` or `catch` blocks. In Java, the `finally` block's `return` statement causes the method to exit with the value 3, regardless of what the `try` block attempted to return.

Answer

The code does not compile.

Answer

2

Answer

1

Question 14

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. Option C is correct because 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 15

Which of the following best demonstrates polymorphism in Java?

Accepted Answer

Using an interface reference to call a method on an implementing object. Polymorphism in Java allows an object to take multiple forms, typically achieved through inheritance and interfaces. Option B demonstrates this by using an interface reference to invoke a method on an implementing object, where the actual method executed is determined at runtime based on the object's class, not the reference type.

Answer

Overloading a method with different parameter lists

Answer

Using static methods

Answer

Overriding a method in a subclass

Answer

Using final methods