1Z0-811 Practice Exam 3 — 20 Questions

Question 1

Refer to the exhibit. Which statement is true about the InvalidInputException class?

Accepted Answer

It is a checked exception.. The InvalidInputException class extends Exception, which makes it a checked exception. Checked exceptions must be either caught or declared in the method signature using 'throws', otherwise the code will not compile. This is the core reason why option B is correct.

Answer

It cannot be thrown by a method.

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It is an unchecked exception.

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It can only be caught in a finally block.

Question 2

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

Accepted Answer

Varargs parameters allow passing zero or more arguments of the specified type.. Varargs (variable-length arguments) in Java allow a method to accept zero or more arguments of a specified type, using the syntax `Type... param`. This is syntactic sugar for an array parameter, and the method body treats it as an array. This enables flexible method invocation without requiring the caller to explicitly create an array.

Answer

If the method modifies elements of the array, the caller does not see the changes.

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If the method assigns a new array to the parameter, the caller's variable is updated.

Question 3

Which THREE are valid ways to declare and initialize an integer variable in Java? (Choose three.)

Accepted Answer

int x = 1_000;. Java allows underscores in numeric literals (introduced in Java 7) to improve readability, and `1_000` is a valid integer literal representing 1000. The compiler simply ignores the underscores during parsing.

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int x = 2.0;

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int x = 0xG;

Question 4

Which design principle is violated by making all fields public in a class?

Accepted Answer

Encapsulation. Making all fields public violates the principle of encapsulation, which requires that an object's internal state be hidden from external access and only modifiable through controlled methods (getters/setters). In Java, public fields allow any class to directly read or modify the field, breaking data integrity and the ability to enforce invariants. Encapsulation is a core OOP concept that protects the internal representation of an object.

Answer

Inheritance

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Abstraction

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Polymorphism

Question 5

A Java class named 'Helper' is defined in package 'utils'. Another class in a different package tries to access a public method of Helper but receives a compilation error. The Helper class is declared as 'class Helper' (without public modifier). What is the likely issue?

Accepted Answer

The class has package-private access. The Helper class is declared with default (package-private) access because no access modifier is specified. Therefore, it is only accessible within the utils package. A class in a different package cannot access it, even if it tries to call a public method of that class, because the class itself is not accessible. The method's access modifier is irrelevant if the class is not accessible. Option A is incorrect because final does not affect access. Option B is incorrect because static is unrelated to access across packages. Option C is incorrect because abstract does not restrict access.

Answer

The method is declared as final

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The method is not static

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The class is abstract

Question 6

What is the output of this program?

Accepted Answer

30
Sum: 1020. The code compiles and runs without error. The first line prints 30 because the loop variable 'i' ends up as 30 due to a bug in the loop logic. The second line prints 'Sum: 1020' because the variable 'sum' holds the value 10 (the loop only sums certain values incorrectly), and the expression 'Sum: ' + sum + '20' concatenates the string 'Sum: ', the integer 10, and the string '20' to produce 'Sum: 1020'. Therefore, option C is correct.

Answer

Runtime exception

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Compilation error

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30
Sum: 30

Question 7

A developer writes a method that accepts a variable number of int arguments and returns their product. Which method signature correctly implements this?

Accepted Answer

public static int product(int... nums). The syntax `int... nums` is the proper Java varargs syntax, allowing a method to accept zero or more `int` arguments, which are then treated as an array inside the method. This enables the developer to call `product(2, 3, 4)` or `product()` and compute the product by iterating over the array.

Answer

public static int product(int[] nums)

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public static int product(int nums...)

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public static int product(int... nums, int extra)

Question 8

A company is developing a configuration manager that must be shared across all components to ensure consistent settings. The manager should prevent direct instantiation and provide a single access point. Which design pattern and implementation should be used?

Accepted Answer

Singleton pattern with a private constructor and a static getInstance() method. The Singleton pattern ensures a class has only one instance and provides a global point of access. A private constructor prevents direct instantiation, and a static getInstance() method provides controlled access.

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Prototype pattern with cloning

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Builder pattern with a static inner class

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Factory pattern with a public constructor

Question 9

Given two String objects s1 = "Hello" and s2 = "Hello", what does the expression (s1 == s2) return?

Accepted Answer

true. The `==` operator compares object references, not string content. Since both `s1` and `s2` are string literals, Java's string interning ensures they refer to the same `String` object in the string constant pool, so `s1 == s2` returns `true`.

Answer

Compilation error

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false

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It depends on the JVM

Question 10

Which two statements about the break statement in Java are true?

Accepted Answer

break can be used inside a switch case. The break statement is used inside a switch case to terminate the switch block and prevent fall-through to subsequent cases. Without break, execution would continue into the next case, which is often unintended.

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break can be used without any enclosing loop

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break is used to skip to next iteration

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break exits the current loop iteration

Question 11

A developer uses a switch statement with a String variable. Which is true about this usage?

Accepted Answer

It works with strings starting from Java 7. Starting from Java 7 (JSR 334), the switch statement supports String objects in addition to primitive types and enums. The compiler uses the `hashCode()` and `equals()` methods of the String class to evaluate the switch expression against case labels, making it a valid and efficient way to branch on string values.

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It works only with primitive types

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It causes a compilation error because strings are not supported

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It requires a default case

Question 12

A developer writes: int a = 9; int b = 2; double result = a / b; System.out.println(result); What is the output?

Accepted Answer

4.0. (4.0). In Java, when dividing two integers, the result is integer division, which truncates the fractional part. So 9 / 2 yields 4 (int). This int value is then assigned to a double variable, resulting in 4.0. Option A (4) would be the result of printing an int, but since result is double, it prints 4.0. Option C is incorrect because the code compiles fine. Option D is incorrect because 4.5 would require at least one operand to be double (e.g., a / (double)b).

Answer

4

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Compilation error

Answer

4.5

Question 13

A developer writes a method that reads a file and processes its contents. The method uses a BufferedReader wrapped around a FileReader. Which of the following approaches ensures that both resources are properly closed even if an exception occurs?

Accepted Answer

Use try-with-resources with both resources declared in the try header.. Try-with-resources ensures that both the BufferedReader and FileReader are automatically closed in reverse order, even if an exception occurs. Option A is wrong because while it attempts to close both resources in separate try-catch blocks within a finally block, this approach is verbose and error-prone; if an exception occurs during the first close, the second close may be skipped unless handled carefully, and it does not guarantee resource closure as reliably as try-with-resources. Option C is wrong because closing only the BufferedReader may close the underlying FileReader due to chaining, but this approach lacks null-safety—if resource creation fails, a NullPointerException occurs when calling close, and it does not demonstrate proper exception handling or best practices. Option D is wrong because throwing a custom exception after closing resources does not ensure both are closed; it adds unnecessary complexity and may leave resources open if close methods throw exceptions.

Answer

Close both resources in a finally block using separate try-catch for each close.

Answer

Close only the BufferedReader in a finally block.

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Throw a custom exception after closing resources in the catch block.

Question 14

During execution, the JVM uses Just-In-Time (JIT) compilation. What is its primary benefit?

Accepted Answer

Improves execution speed by compiling frequently used bytecode to native code.. JIT compilation improves execution speed by compiling frequently used bytecode into native machine code at runtime. Option A is incorrect because JIT does not translate bytecode into an intermediate language; it compiles to native code. Option C is incorrect because JIT compiles bytecode, not source code. Option D is incorrect because JIT's primary purpose is performance, not security.

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Translates bytecode into an intermediate language for interpretation.

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Converts Java source code directly into bytecode.

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Enhances security by verifying bytecode integrity.

Question 15

A developer is writing a bitmask validation method. The method should return true if both input integers (x and y) have exactly the same least significant bit set. The developer writes: if (x & y == 1) { return true; } However, the condition never evaluates to true even when both numbers are odd (least significant bit = 1). Debugging shows that x and y are positive integers. What is the root cause and the correct fix?

Accepted Answer

Add parentheses: if ((x & y) == 1) { ... }. In Java, the bitwise AND operator & has lower precedence than the equality operator ==. So x & y == 1 is parsed as x & (y == 1), which first evaluates y == 1 to a boolean, then performs bitwise AND with x, treating true as 1 and false as 0. That's not the intended check. The correct fix is to add parentheses to ensure & is evaluated first: (x & y) == 1. This checks if both numbers have the same least significant bit set (both odd). Option B correctly adds parentheses. Options A, C, and D do not correctly address the bitwise check: A uses modulo which works for odd/even but not general bitmasking; C uses bitwise OR which checks if either bit is set; D uses logical AND which is for booleans, not integers.

Answer

Use modulo: if (x % 2 == 1 && y % 2 == 1) { ... }

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Use bitwise OR: if (x | y == 1) { ... }

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Use logical AND: if (x && y == 1) { ... }

Question 16

What is the primary role of the Java Development Kit (JDK) compared to the JRE?

Accepted Answer

JDK includes compilers and tools for developing Java applications.. The JDK (Java Development Kit) is a software development environment used for developing Java applications. It includes the JRE (Java Runtime Environment) plus development tools such as the Java compiler (javac), debugger, and other utilities. In contrast, the JRE provides only the runtime environment needed to run Java applications. Therefore, option D is correct because the JDK includes compilers and tools for development. Option A is incorrect because the JDK provides far more than just a debugger and profiler; it includes the compiler and other essential tools. Option B is incorrect because the JDK includes the JRE, not the other way around. Option C is incorrect because the JRE is required to run Java applications, while the JDK is needed for development; the JDK is not required to run applications.

Answer

JDK provides only a debugger and profiler.

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JRE includes the JDK and additional libraries.

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JDK is required to run Java applications, whereas JRE is not.

Question 17

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

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Runtime exception

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Compilation fails

Question 18

Which TWO of the following are valid benefits of using inheritance in Java? (Choose two.)

Accepted Answer

Allows polymorphic behavior. Options B and C are correct. Inheritance promotes code reuse by allowing subclasses to reuse fields and methods from superclasses, reducing redundancy. It also enables polymorphic behavior through method overriding, allowing objects to be treated as instances of their parent class. Option A is incorrect because inheritance actually increases coupling between classes, which is generally considered a disadvantage, not a benefit. Option D is incorrect because encapsulation is enforced through access modifiers (private, protected, public), not inheritance. Option E is incorrect because inheritance can actually complicate debugging by introducing dependencies across classes.

Answer

Increases coupling between classes

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Enforces encapsulation

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Simplifies debugging

Question 19

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

Accepted Answer

boolean. (boolean) is correct because boolean is one of the eight primitive data types in Java, representing a single bit of information with only two possible values: true or false. It is not an object and does not have methods, unlike reference types such as Boolean (the wrapper class).

Answer

void

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String

Question 20

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

Accepted Answer

The intern() method returns a String from the pool. The `intern()` method returns a canonical representation of the string from the string pool, ensuring that strings with the same content share the same memory reference, which is a key aspect of immutability and memory optimization in Java.

Answer

String objects can be modified after creation

Answer

String objects can be changed by calling methods