1Z0-811 Practice Test 20 — 15 Questions

Question 1

Which of the following statements about the String class is true?

Accepted Answer

Strings are immutable. String objects in Java are immutable, meaning once a String object is created, its value cannot be changed. Any operation that appears to modify a String, such as concatenation, actually creates a new String object. This immutability is a fundamental design choice that enables String pooling, thread safety, and efficient caching of hash codes.

Answer

Strings can be modified using the '+' operator

Answer

String objects can be created only with the 'new' keyword

Answer

String is a primitive type

Question 2

A developer writes the following code:

public class Test {
    public static void main(String[] args) {
        int[] a = {1, 2, 3};
        int[] b = a;
        b[0] = 99;
        System.out.println(a[0] + " " + b[0]);
    }
}

What is the output?

Accepted Answer

99 99. Array variables hold references to array objects. The statement int[] b = a copies the reference, not the array contents, so both variables point to the same object. Any modification through one reference is visible through the other. Thus, after b[0] = 99, both a[0] and b[0] evaluate to 99, and the program prints 99 99.

Answer

Compilation fails because you cannot assign an int array to another int array variable.

Answer

1 1

Answer

1 99

Question 3

Which two statements are true about primitive data types in Java?

Accepted Answer

The long data type can store values from -2^63 to 2^63-1.. Option A is correct because long is a 64-bit signed two's-complement integer, giving an exact range of -2^63 to 2^63-1. Option B is correct because short is a 16-bit signed integer, whose range is exactly -32,768 to 32,767. Option C is wrong because float is a 32-bit IEEE 754 binary floating-point type and cannot represent most decimal values precisely. Option D is wrong because the JVM does not define a precise size for boolean; its "size" is implementation-dependent and not fixed at 1 bit. Option E is wrong because char is a 16-bit unsigned UTF-16 code unit, so it can hold far more than ASCII characters.

Answer

The float data type is 32-bit and can represent decimal numbers precisely.

Answer

The boolean data type has a size of 1 bit.

Answer

The char data type can store only ASCII characters.

Question 4

A class has two methods: void setValue(int a) and void setValue(double a). Which call will result in a compilation error?

Accepted Answer

setValue(5); setValue(5.0); both in same class. Since the class contains both overloaded methods void setValue(int a) and void setValue(double a), all the provided calls are valid and compile without error. setValue(5) calls the int version, setValue(5.0) calls the double version, and setValue((int)5.0) explicitly casts to int, calling the int version. Option B consists of two separate valid calls within the same class, so no compilation error occurs. Therefore, none of the options result in a compilation error.

Answer

setValue(5.0);

Answer

setValue(5);

Answer

setValue((int)5.0);

Question 5

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 is designed to minimize pause times by dividing the heap into regions and prioritizing the collection of regions with the most garbage (hence 'Garbage-First'). It allows the user to specify a target pause time via -XX:MaxGCPauseMillis, and it performs incremental collections, often avoiding full heap compactions. This makes it suitable for applications where low latency is critical, such as the one described with frequent Full GC pauses.

Answer

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

Answer

Serial GC (-XX:+UseSerialGC)

Answer

Parallel GC (-XX:+UseParallelGC)

Question 6

Which statement about the Java compiler is true?

Accepted Answer

It translates Java source code into bytecode.. The Java compiler (javac) translates human-readable Java source code (.java files) into platform-independent bytecode (.class files). This bytecode is then executed by the Java Virtual Machine (JVM), not directly by the operating system. Option D correctly identifies this translation step.

Answer

It translates Java source code into native machine code.

Answer

It produces executable files that run directly on the OS.

Answer

It executes Java programs.

Question 7

Which primitive type has a default value of 0.0f?

Accepted Answer

float. In Java, the default value for a float primitive is 0.0f. This is because float is a 32-bit IEEE 754 floating-point type, and its default initialization is 0.0f (with the 'f' suffix to denote a float literal). Option A is correct because it directly matches this specification.

Answer

long

Answer

double

Answer

int

Question 8

Which of the following exceptions is a checked exception?

Accepted Answer

IOException. 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 9

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

Accepted Answer

The default constructor has no parameters. Option A is correct because the default constructor is a no-argument constructor that the compiler generates when no constructor is explicitly declared, and it takes no parameters. Option C is correct because a constructor never has a return type and cannot return a value; it only initializes the new object, and any declared return type would make it a regular method. Option D is correct because constructors can be overloaded, meaning a class may define multiple constructors with different parameter lists to provide different initialization paths. Option B is not correct because constructors cannot be abstract; abstract applies to classes and methods, and a constructor is never inherited or overridden in that way. Option E is not correct because constructors cannot be final, since final is not a permitted modifier for constructors and they are not overridden like methods.

Answer

Constructors can be abstract

Answer

Constructors can be final

Question 10

Arrange the steps to declare and initialize a one-dimensional array in Java in the correct order.

Accepted Answer

Step 1: Declare array variable (e.g., int[] arr;), Step 2: Allocate memory using new keyword (e.g., arr = new int[5];), Step 3: Assign values to elements (e.g., arr[0] = 1; arr[1] = 2; ...).. The process involves declaring the array variable, then assigning it a new array or initializer, and optionally providing initial values.

Answer

Step 1: Allocate memory using new keyword, Step 2: Declare array variable, Step 3: Assign values.

Answer

Step 1: Assign values to elements, Step 2: Declare array variable, Step 3: Allocate memory.

Answer

Step 1: Declare array variable, Step 2: Assign values to elements, Step 3: Allocate memory.

Question 11

Which of the following is a valid Java primitive type?

Accepted Answer

boolean. `boolean` is one of the eight primitive data types defined in the Java Language Specification (JLS §4.2). It represents a single bit of information with only two possible values: `true` or `false`, and is not an object or a reference type.

Answer

String

Answer

Integer

Answer

Char

Question 12

Arrange the steps to handle an exception using try-catch-finally in Java in the correct order.

Accepted Answer

try block, then catch block, then finally block. The try block contains risky code, catch handles the exception, and finally executes cleanup. The order is try, catch, then finally.

Answer

catch block, then try block, then finally block

Answer

finally block, then try block, then catch block

Answer

try block, then finally block, then catch block

Question 13

Arrange the steps to overload a method in Java in the correct order.

Accepted Answer

Define a method, then define another method with the same name but different parameters, then ensure the method signatures are unique, then call the method with arguments that match one of the signatures.. First define one method, then define another with same name but different parameters, ensure unique signatures, and then call with matching arguments.

Answer

Define a method, then ensure the method signatures are unique, then define another method with the same name but different parameters, then call the method with arguments.

Answer

Define another method with the same name but different parameters, then define a method, then ensure unique signatures, then call the method.

Answer

Call the method with arguments, then define a method, then define another method with the same name but different parameters, then ensure unique signatures.

Question 14

A team is developing a Java application for an online store. The application has a class 'Inventory' that maintains an array of 'Product' objects. The method 'public void addProduct(Product p)' is intended to add a product to the array. The current implementation uses a fixed-size array of length 100. However, the business has grown, and the array may exceed its capacity. The team needs a solution that allows dynamic resizing without changing the method signature. Which approach should the team take?

Accepted Answer

Modify the method to use an ArrayList internally and keep the signature.. Using an ArrayList internally allows the array to dynamically resize as needed, while keeping the method signature unchanged. The method still accepts a Product parameter, but the internal implementation leverages ArrayList's automatic capacity management, eliminating the fixed-size constraint.

Answer

Change the method signature to accept a Product[] array and copy all elements.

Answer

Use a Collection<Product> as parameter and convert to array.

Answer

Change the return type to boolean and return false if array is full.

Question 15

Refer to the exhibit. A developer encounters this exception when running the application. The method divide is intended to handle division by zero. What is the most likely cause of the exception?

Accepted Answer

The divide method uses integer division without checking the divisor.. The exception is most likely an ArithmeticException thrown because the divide method performs integer division without checking if the divisor is zero. In Java, dividing an int by zero throws ArithmeticException at runtime; the method must explicitly check the divisor or catch the exception. Since the method is 'intended to handle division by zero' but still throws, the cause is the missing divisor check.

Answer

The divide method does not catch ArithmeticException.

Answer

The JVM is not configured to handle arithmetic exceptions.

Answer

The Main class does not declare throws ArithmeticException.