1Z0-811 Practice Test 14 — 15 Questions

Question 1

What is the output when the main method is executed?

```java
public class Test {
    public static double add(double a, double b) {
        return a + b;
    }
    public static void main(String[] args) {
        System.out.println(add(5, 10));
    }
}
```

Accepted Answer

15.0. The code defines a single method `public static double add(double a, double b) { return a + b; }`. The main method calls `System.out.println(add(5,10));`. Java performs implicit widening conversion of the integer literals 5 and 10 to double, resulting in 15.0. Options 5.0 and 10.0 would be incorrect because the method adds the arguments. Option D is incorrect because there is no ambiguity — only one method matches after widening.

Answer

5.0

Answer

10.0

Answer

Compilation error: ambiguous method call

Question 2

A developer needs to build a SQL query string by concatenating many parts. Which approach is most efficient for repeated concatenation?

Accepted Answer

Using StringBuilder.append(). StringBuilder.append() is the most efficient choice for repeated concatenation because StringBuilder is a mutable, non-synchronized sequence of characters that appends in amortized O(1) time without allocating a new String on each operation. For a single-threaded SQL-building loop, this avoids the O(n²) allocation churn of `+=` and the unnecessary synchronization overhead of StringBuffer.

Answer

Using StringBuffer.append()

Answer

Using String concatenation with +=

Answer

Using String.concat()

Question 3

Which THREE of the following are checked exceptions in Java?

Accepted Answer

java.sql.SQLException. java.sql.SQLException (A) is a checked exception because it extends java.lang.Exception (via java.sql.SQLException's hierarchy) and is not a subclass of RuntimeException, so the compiler requires it to be declared or caught. java.lang.ClassNotFoundException (C) is also a checked exception, extending java.lang.ReflectiveOperationException (which extends Exception), and must be handled or declared when using methods like Class.forName(). java.io.IOException (E) is a checked exception extending java.lang.Exception, commonly required to be handled for I/O operations. In contrast, java.lang.NullPointerException (B) and java.lang.ArithmeticException (D) are both subclasses of java.lang.RuntimeException, making them unchecked exceptions that do not require explicit handling.

Answer

java.lang.NullPointerException

Answer

java.lang.ArithmeticException

Question 4

Which two of the following are fundamental principles of Object-Oriented Programming? (Choose two.)

Accepted Answer

Encapsulation. Encapsulation (D) is a fundamental OOP principle because it bundles data (attributes) and the methods that operate on that data within a single class, while restricting direct external access through access modifiers such as private, protected, and public, exposing behavior only via well-defined interfaces. Polymorphism (E) is also fundamental because it lets a single interface or method name represent different underlying forms, enabling one reference type to invoke behavior that is resolved at runtime through overriding (dynamic dispatch) or at compile time through overloading. The remaining options are not OOP principles: iteration (A) is a general control-flow construct for repeating statements (loops such as for and while), compilation (B) is the process of translating source code into bytecode or machine code performed by a compiler, and synchronization (C) is a concurrency mechanism for coordinating access to shared resources, typically via locks, monitors, or the synchronized keyword.

Answer

Iteration

Answer

Compilation

Answer

Synchronization

Question 5

A developer is working on a Java application that processes user input. The application reads an integer from the command line using args[0], converts it to an int, and uses it in a loop. When testing, the application throws a NumberFormatException when the user provides an alphabetic string. The developer needs to handle this exception gracefully by prompting the user to enter a valid number and retrying. However, the developer must avoid infinite loops. The current code uses a while loop with a flag. Which approach ensures the code handles the exception, provides feedback, and terminates if the user enters 'quit'? The environment is a standard Java SE 11 application. The developer wants a robust solution without using external libraries.

Accepted Answer

Use a try-catch inside a loop that continues if exception caught, and breaks if input equals 'quit' or conversion succeeds.. It uses a try-catch inside a while loop that continues if an exception is caught, allowing the user to re-enter input. The loop also checks if the input equals 'quit' to break out, ensuring the program can terminate gracefully. This approach provides feedback (prompting the user) and avoids infinite loops. Option B is incorrect because ignoring the exception would not provide feedback or allow retry. Option C is incorrect because it never checks for 'quit', risking an infinite loop. Option D is incorrect because calling System.exit(0) terminates the program abruptly, which is not graceful.

Answer

Catch the exception and ignore it; the loop will naturally terminate.

Answer

Use a do-while loop that never checks for 'quit'; the exception is caught outside the loop.

Answer

Catch the exception in the loop and call System.exit(0) immediately.

Question 6

Which three statements about String immutability are true? (Choose three)

Accepted Answer

The intern() method returns a String from the pool. Option C is correct because String.intern() checks the string pool and returns the canonical pooled instance, so calling intern() on an equal string yields a reference to the pool's String rather than a new object. Option D is correct because String is immutable, so concatenation with + or concat() cannot alter the original object; it produces a new String instance containing the combined characters. Option E is correct because StringBuilder provides a mutable character sequence whose append/insert/delete methods modify the same object, which is the standard alternative when repeated String modification would create many new Strings. Options A and B are incorrect because immutability means a String's character content cannot be modified after creation, and no String method can change the existing object's value; methods like toUpperCase() or substring() return new String objects instead.

Answer

String objects can be modified after creation

Answer

String objects can be changed by calling methods

Question 7

Which THREE of the following are key features of the Java programming language?

Accepted Answer

Platform independence through bytecode and JVM. Option C is correct because Java source is compiled to platform-neutral bytecode that runs on any system with a Java Virtual Machine (JVM), which is the essence of Java's 'write once, run anywhere' design. Option D is correct because Java performs automatic memory management via garbage collection, reclaiming heap objects no longer referenced so developers don't manually free memory. Option E is correct because Java enforces strong static type checking at compile time, catching type mismatches before execution and ensuring type safety. Option A is incorrect because Java deliberately omits pointer arithmetic and direct memory access for safety, offering only references. Option B is incorrect because Java allows multiple inheritance only for interfaces, not for classes, to avoid the diamond problem.

Answer

Use of pointers for direct memory access

Answer

Support for multiple inheritance of classes

Question 8

Which THREE statements are true about the Java logging API (java.util.logging)?

Accepted Answer

Handlers can be attached to loggers to output messages. Option A is correct because java.util.logging uses Handler objects (such as ConsoleHandler, FileHandler, or SocketHandler) that are attached to a Logger via addHandler() to publish LogRecords to a destination. Option C is correct because Loggers form a hierarchical, dot-separated namespace (e.g., com.example.app is a child of com.example), and child loggers inherit handlers and levels from their ancestors. Option E is correct because each Logger has its own Level set via setLevel(), and a LogRecord is only processed if its level is greater than or equal to the logger's effective level. Option B is not correct because the default logging.properties sets the root logger level to INFO, not FINEST. Option D is not correct because messages are only forwarded up the hierarchy to ancestor loggers (ultimately the root) when useParentHandlers is true, which is the default but can be disabled, so it is not automatic for all loggers.

Answer

The default configuration logs all messages at FINEST level

Answer

All loggers automatically forward messages to the root logger

Question 9

A developer creates an interface 'Drawable' with a single abstract method 'draw()'. They then create a class 'Circle' that implements Drawable but forgets to provide the draw() method. Circle is not declared abstract. What will happen when compiling Circle?

Accepted Answer

Compilation fails because Circle must either implement draw() or be declared abstract. In Java, a concrete class that implements an interface must provide implementations for all abstract methods of that interface. If Circle does not implement draw() and is not declared abstract, the compiler reports an error because the class is incomplete. The fix is either to implement draw() or to mark Circle as abstract.

Answer

Compilation fails because interfaces cannot be implemented without overriding all methods

Answer

Compilation succeeds, a default empty method is generated

Answer

Compilation succeeds but a warning is issued

Question 10

Given the code: int[] arr = {1,2,3}; for(int x : arr) { if(x==2) continue; System.out.print(x); } What is the output?

Accepted Answer

13. The enhanced for loop iterates over the array {1,2,3}. When x equals 2, the continue statement skips the remainder of the loop body for that iteration, so System.out.print(x) is not executed for 2. Thus, only 1 and 3 are printed, producing output '13'.

Answer

2

Answer

Compilation error

Answer

123

Question 11

Which THREE of the following are valid loop constructs in Java?

Accepted Answer

while loop. The while loop (A) is a valid Java loop construct that repeatedly executes a statement or block as long as its boolean condition remains true, checking the condition before each iteration. The for loop (B) is also valid, providing a compact header with initialization, condition, and update expressions to control iteration, including the enhanced for-each form for arrays and Iterables. The do-while loop (E) is valid as well, executing its body at least once and then repeating while its boolean condition is true, since the condition is evaluated after the body. The switch statement (C) is a selection/branching construct, not a loop, and the if statement (D) is a conditional branching construct, so neither repeats execution on its own and neither belongs among Java's loop constructs.

Answer

switch statement

Answer

if statement

Question 12

Which THREE are valid components of the Java Virtual Machine (JVM)?

Accepted Answer

Heap memory area. The JVM's runtime data areas include the heap memory area (C), which stores all class instances and arrays and is shared across threads, making it a core internal component of the JVM. The execution engine (D) is also a fundamental JVM component: it executes bytecode via an interpreter, and may include a JIT compiler and garbage collector. The class loader subsystem (E) is the JVM component responsible for loading, linking, and initializing classes (bootstrap, extension/platform, and application class loaders), so it is likewise a valid JVM component. By contrast, Java source code (.java files) (A) is human-readable input to the compiler, not part of the JVM, and the Java compiler javac (B) is a separate JDK tool that produces bytecode before the JVM is involved, so neither belongs to the JVM's internal architecture.

Answer

Java source code (.java files)

Answer

Java compiler (javac)

Question 13

Which THREE are valid loop constructs in Java? (Choose three.)

Accepted Answer

while (condition) { }. The `while` loop is a standard Java construct that repeatedly executes a block of code as long as the specified boolean condition evaluates to `true`. The syntax `while (condition) { }` is valid even with an empty body, as the condition is checked before each iteration.

Answer

repeat { } until (condition);

Answer

loop (condition) { }

Question 14

What is the value of the expression (10 > 5) && (3 < 2)?

Accepted Answer

false. The expression (10 > 5) evaluates to true, and (3 < 2) evaluates to false. The logical AND operator (&&) returns true only if both operands are true. Since one operand is false, the entire expression evaluates to false. In Java, the result of a boolean expression is a boolean literal, not an integer.

Answer

1

Answer

true

Answer

0

Question 15

A security-sensitive class should not be extended by any other class. Which modifier should be applied to the class declaration?

Accepted Answer

final. The final modifier on a class declaration prevents any other class from extending it. Applying final to the security-sensitive class enforces the design constraint at compile time, so any attempt to subclass it produces a compilation error. This is the standard Java mechanism for sealing a class against inheritance.

Answer

abstract

Answer

static

Answer

private