1Z0-811 Practice Test 19 — 15 Questions

Question 1

Which THREE are fundamental principles of Object-Oriented Programming? (Choose three.)

Accepted Answer

Encapsulation. Options B, D, and E are correct. Encapsulation, inheritance, and polymorphism are the three fundamental principles of Object-Oriented Programming. Option A (Compilation) is incorrect because compilation is a language process, not an OOP principle. Option C (Modularization) is incorrect because modularization is a design concept, not a foundational OOP principle.

Answer

Compilation

Answer

Modularization

Question 2

Which TWO are best practices for using control flow statements? (Choose two.)

Accepted Answer

Use the enhanced for loop instead of the traditional for loop when iterating over arrays.. Options A and B are correct. A is correct because the enhanced for loop (for-each) is less error-prone and more readable when iterating over arrays or collections. B is correct because break statements can improve efficiency by allowing early exit from a loop when a condition is met, avoiding unnecessary iterations. C is wrong because deeply nested if-else blocks harm readability and maintainability; alternatives like switch or early returns are preferred. D is wrong because switch statements are often more readable and efficient than long else-if chains for multi-way branches based on a single value. E is wrong because Java does not support goto statements; its control flow uses structured constructs like break/continue with labels.

Answer

Use deeply nested if-else blocks to handle all possible conditions.

Answer

Prefer multiple else-if chains over switch statements for multi-way branches.

Answer

Use a goto statement to jump out of nested loops.

Question 3

Which three statements about the switch statement in Java are true?

Accepted Answer

a break statement is optional. Options A, B, and D are true. A: The break statement is optional; without it, execution falls through to the next case. B: char can be used as the switch expression type because char is an integer-compatible type. D: The default case executes when no other case matches. C is false because only one default case is allowed. E is false because boolean is not allowed as a switch expression.

Answer

the switch statement can have multiple default cases

Answer

switch can use boolean as the expression type

Question 4

A junior developer created a class 'BankAccount' with public fields for balance and account number. After deployment, users are able to set negative balances, causing issues. Which OOP principle should have been applied to prevent this?

Accepted Answer

Encapsulation. Encapsulation involves making fields private and providing controlled access via methods. By encapsulating the balance field, a setter method can validate that the balance is not set to a negative value, preventing the issue. Option A (Inheritance) is about code reuse, not data hiding. Option C (Abstraction) is about hiding complexity, not enforcing validation. Option D (Polymorphism) is about methods behaving differently, not data protection.

Answer

Inheritance

Answer

Abstraction

Answer

Polymorphism

Question 5

A company's legacy code has a method that takes an array of integers and returns a new array containing only the positive numbers. The current implementation uses a fixed-size array equal to the input size and counts positive numbers, then copies them, but if many negatives exist, the result array has trailing zeros (which are removed by copying again). This wastes memory and time. The array can be large (up to 1 million elements). The developer wants to improve memory efficiency and runtime without using external libraries. Which approach should they implement?

Accepted Answer

First count positives, then create an array of that exact size, fill it.. It avoids the overhead of dynamic resizing (as in ArrayList) or boxing (as in streams) by first counting the positives in a single pass, then creating an exact-sized int[] array, and filling it in a second pass. This yields O(n) time complexity and minimal memory overhead, directly addressing the legacy code's inefficiency without external libraries.

Answer

Use an ArrayList to collect positive numbers, then convert to int[].

Answer

Use a stream to filter and collect to array.

Answer

Use a linked list and then convert.

Question 6

Which THREE statements are true about interfaces in Java? (Choose three.)

Accepted Answer

An interface can extend multiple interfaces. Options B, C, and D are true about interfaces in Java. An interface can extend multiple interfaces using the extends keyword. Since Java 8, interfaces can contain static methods (with body) and default methods. Option A is false because interfaces cannot be instantiated directly; they must be implemented by a class. Option E is false because interface fields are implicitly public static final; private fields are not permitted in interfaces (private methods are allowed since Java 9, but not fields).

Answer

An interface can be instantiated directly

Answer

An interface can have private fields

Question 7

A Java application uses an interface 'Drawable' with a default method 'draw()'. A class 'Circle' implements Drawable but does not override draw(). Another class 'Square' implements Drawable and overrides draw(). Which statement is true about calling draw() on instances of Circle and Square?

Accepted Answer

Circle will use the default, Square will use its own. When a class implements an interface with a default method, the class inherits the default implementation unless it overrides the method. Circle does not override draw(), so it uses the default implementation from the Drawable interface. Square overrides draw(), so it uses its own version. Option B is incorrect because Square uses its own method, not the default. Option C is incorrect because Square does not use the default. Option D is incorrect because both classes compile successfully.

Answer

Square will use the default, Circle will cause a compilation error

Answer

Both will use the default implementation

Answer

Both will cause a compilation error

Question 8

A class 'Animal' has a method 'makeSound()'. Subclasses 'Dog' and 'Cat' override it. When calling makeSound() on an Animal reference that actually holds a Dog object, the Dog's version is executed. This is an example of:

Accepted Answer

Dynamic binding. Dynamic binding. Dynamic binding (runtime polymorphism) resolves method calls based on the actual object type at runtime, not the reference type. Here, the Animal reference holds a Dog object, so the Dog's overridden makeSound() is invoked. A is wrong because static binding occurs at compile-time for methods that cannot be overridden (e.g., static, final, or private). B is wrong because encapsulation hides data, not method dispatch. D is wrong because method overloading is compile-time polymorphism based on method signature.

Answer

Static binding

Answer

Encapsulation

Answer

Method overloading

Question 9

Refer to the exhibit. What is the output?

Accepted Answer

17. The expression `a * b + 2` follows Java operator precedence: multiplication has higher precedence than addition, so it evaluates as `(a * b) + 2`. Given `a = 3` and `b = 5`, `3 * 5 = 15`, then `15 + 2 = 17`. Therefore, option C is correct. Option A is wrong because the code compiles successfully (no error). Option B (25) would result from `(a + b) * 2` or similar misinterpretation. Option D (21) would result from `a * (b + 2)`. Only option C matches the correct calculation.

Answer

Compilation error

Answer

25

Answer

21

Question 10

A team deploys a Java application and observes frequent Full GC pauses. Which garbage collector is designed to minimize pause times?

Accepted Answer

Garbage-First (G1GC) (-XX:+UseG1GC). G1GC (Garbage-First) is designed to provide predictable pause times and minimize Full GC pauses by dividing the heap into regions and collecting the regions with the most garbage first. Option B (CMS) was also designed for low pauses but is deprecated and can cause fragmentation. Option C (Serial) is for single-threaded environments and has long pauses. Option D (Parallel) focuses on throughput, not pause times.

Answer

Concurrent Mark Sweep (CMS) (-XX:+UseConcMarkSweepGC)

Answer

Serial GC (-XX:+UseSerialGC)

Answer

Parallel GC (-XX:+UseParallelGC)

Question 11

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 12

Which TWO are true about the Java Runtime Environment (JRE)? (Choose two.)

Accepted Answer

It includes the JVM. The JRE (Java Runtime Environment) includes the JVM (Java Virtual Machine) and core libraries necessary to run Java applications. Therefore, option C is correct. Option E is correct because the JRE is required to run any Java application; without it, Java bytecode cannot be executed. Option A is incorrect: the JRE is smaller than the JDK (Java Development Kit) because the JDK contains additional tools like the compiler and debugger. Option B is incorrect: the Java compiler is part of the JDK, not the JRE. Option D is incorrect: development tools are included in the JDK, not the JRE.

Answer

It is larger than the JDK

Answer

It includes the Java compiler

Answer

It includes development tools

Question 13

Given the output, which statement is true about this Java installation?

Accepted Answer

It includes a Just-In-Time (JIT) compiler.. The output shows 'mixed mode', meaning the JVM uses both an interpreter and a Just-In-Time (JIT) compiler. In a standard Java SE installation, HotSpot VM includes a JIT compiler for performance optimization. Option B is incorrect because interpreted-only mode would require the -Xint flag. Option C is incorrect because a debug build typically includes 'debug' in the version string. Option D is incorrect because Java ME is for embedded devices and would not show a standard HotSpot VM.

Answer

It runs only in interpreted mode without JIT.

Answer

It is a debug build of the JVM.

Answer

It is a Java Micro Edition (Java ME) runtime.

Question 14

A developer has written a Java program that uses third-party libraries. Which TWO actions are necessary to run the program on a different machine? (Choose two.)

Accepted Answer

Set the PATH environment variable to include the java executable. Options C and D are correct. To run a Java program, the JRE must be installed (D) because it provides the Java Runtime Environment including the JVM. The PATH must include the java executable's directory (C) so that the 'java' command can be invoked. Option A is incorrect because .class files alone are insufficient; third-party libraries (JARs) are also needed and must be accessible. Option B is incorrect because the JDK (Java Development Kit) is only needed for compilation and development, not for running. Option E is incorrect because source files are not required to run the compiled program.

Answer

Copy only the .class files of the program

Answer

Install the JDK

Answer

Copy the .java source files

Question 15

Which TWO statements are true about the 'super' keyword in Java?

Accepted Answer

It can be used to call a superclass method that has been overridden.. The 'super' keyword can be used to call a superclass method that has been overridden, using 'super.methodName()'. Option D is correct because 'super()' invokes the superclass constructor. Option A is wrong because 'super' cannot access private methods of the superclass. Option B is wrong because 'super' cannot access private fields. Option E is wrong because 'super' cannot invoke static methods directly; static methods are accessed via the class name.

Answer

It can be used to access private methods of the superclass.

Answer

It can be used to access private fields of the superclass.

Answer

It can be used to invoke a static method of the superclass.