1Z0-811 Practice Test 28 — 15 Questions

Question 1

Which THREE of the following expressions evaluate to true? (Assume int a=5, b=10)

Accepted Answer

a < b. The expression 'a < b' compares the integer values of a (5) and b (10). Since 5 is less than 10, the relational operator '<' returns the boolean value true.

Answer

a == b

Answer

a >= b

Question 2

A method is designed to reverse an array of integers. The method signature is: public static void reverse(int[] arr). The method correctly reverses the array. Which statement is true about the method?

Accepted Answer

It modifies the original array.. The method receives a reference to the array (pass-by-value of the reference), so any modifications made to the array elements inside the method directly affect the original array object in the caller's scope. Since the method reverses the array in-place by swapping elements, the original array is mutated.

Answer

It returns a new array that is the reverse of the input.

Answer

It cannot be called with a null array.

Answer

It uses pass-by-value, so the original array is unchanged.

Question 3

Which TWO statements are true about method overloading in Java?

Accepted Answer

Overloaded methods can have different parameter lists.. Method overloading in Java allows multiple methods to share the same name but have different parameter lists (different number, type, or order of parameters). This enables compile-time polymorphism, where the compiler selects the appropriate method based on the arguments provided at the call site.

Answer

Overloaded methods must have the same number of parameters.

Answer

Overloaded methods must have different return types.

Answer

Overloaded methods can have different names.

Question 4

Given int[] arr = {1,2,3}; which correctly creates a new array with length 5 and copies the contents of arr?

Accepted Answer

int[] newArr = Arrays.copyOf(arr, 5);. `Arrays.copyOf(int[] original, int newLength)` creates a new array of the specified length (5) and copies the elements from the original array into it, padding with default values (0 for int) for any extra positions. This method is specifically designed for this task, ensuring the original array remains unchanged.

Answer

int[] newArr = new int[5]; newArr = arr;

Answer

int[] newArr = arr.clone(); newArr.length = 5;

Answer

int[] newArr = Arrays.copy(arr, 5);

Question 5

Which of the following is a valid declaration of a float variable?

Accepted Answer

Both B and D are valid. Options B and D are valid because they use the f or F suffix to explicitly denote a float literal. Option C is invalid because 10.5 is a double literal and cannot be implicitly converted to float without a cast or suffix.

Answer

float f = 10.5f;

Answer

float f = 10.5;

Answer

float f = 10.5F;

Question 6

Which THREE are checked exceptions in Java? (Choose three.)

Accepted Answer

SQLException. SQLException is a checked exception in Java because it extends Exception directly (not RuntimeException). Checked exceptions must be either caught with a try-catch block or declared in the method signature using the throws clause. SQLException is thrown when there is a database access error or other SQL-related issues, forcing the developer to handle potential failures at compile time.

Answer

ArrayIndexOutOfBoundsException

Answer

NullPointerException

Question 7

A developer is working on a Java application that processes user input. The application reads a string from the console and needs to compare it with a predefined constant string "ADMIN". The developer writes the following code: if (input == "ADMIN") { grantAccess(); }. During testing, the condition sometimes fails even when the user enters ADMIN. The input string is obtained via Scanner.nextLine(). Which is the most likely cause and best fix?

Accepted Answer

Use input.equals("ADMIN") instead of ==.. `==` compares object references, not string content. `Scanner.nextLine()` returns a new `String` object, so `input == "ADMIN"` compares references, which are different even if the content matches. Using `input.equals("ADMIN")` compares the actual character sequence, which is the correct way to test string equality in Java.

Answer

Use input.compareTo("ADMIN") == 0.

Answer

Use input == "ADMIN" with intern() on input.

Answer

Convert input to char array and compare.

Question 8

Which TWO of the following are valid Java identifiers? (Choose 2)

Accepted Answer

$value. ($value) is correct because Java allows identifiers to begin with a dollar sign ($) or underscore (_), and the rest can include letters, digits, or these special characters. The dollar sign is a valid starting character per the Java Language Specification (JLS §3.8), so $value is a legal identifier.

Answer

my#var

Answer

my-var

Answer

2ndPlace

Question 9

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

Accepted Answer

The default constructor has no parameters. Constructors can be overloaded to provide different initialization options, they cannot return a value (not even void), and if no constructor is defined, the compiler provides a default no-arg constructor.

Answer

Constructors can be abstract

Answer

Constructors can be final

Question 10

What is the output of the following code? int[] a = {1,2,3}; int[] b = a; b[0] = 99; System.out.println(a[0]);

Accepted Answer

99. In Java, arrays are reference types. When `int[] b = a;` is executed, `b` does not create a new array; it simply references the same array object as `a`. Therefore, modifying `b[0]` directly changes the element in the original array `a`, so `a[0]` prints 99.

Answer

0

Answer

1

Answer

Compilation error

Question 11

Given the stack trace above, which line in MyClass.java caused the exception?

Exception in thread "main" java.lang.NullPointerException
    at MyClass.methodC(MyClass.java:25)
    at MyClass.methodB(MyClass.java:15)
    at MyClass.methodA(MyClass.java:10)
    at MyClass.main(MyClass.java:30)

Accepted Answer

Line 25. The stack trace displayed in the question shows the exception was thrown at line 25 of MyClass.java. The topmost line in a stack trace indicates the exact line where the exception originated. Lines 10, 15, and 30 correspond to caller methods that appear lower in the stack trace, making line 25 the correct answer.

Answer

Line 30

Answer

Line 10

Answer

Line 15

Question 12

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

Accepted Answer

Exception. 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 13

Given: String str = "Java"; str = str.concat(" SE"); str.replace('a', 'A'); System.out.println(str); What is the output?

Accepted Answer

Java SE. The `concat` method returns a new String "Java SE" which is assigned back to `str`. The `replace` method also returns a new String but its result is not assigned to any variable, so the original `str` remains unchanged. The final `println` outputs the current value of `str`, which is "Java SE".

Answer

Java

Answer

JAVA SE

Answer

JAvA SE

Question 14

Which primitive data type should be used to store a single character?

Accepted Answer

char. The `char` primitive data type in Java is specifically designed to store a single 16-bit Unicode character, ranging from '\u0000' (0) to '\uffff' (65,535). It can represent any character in the Unicode standard, including letters, digits, and symbols, making it the appropriate choice for a single character value.

Answer

int

Answer

byte

Answer

String

Question 15

Which THREE statements about the final keyword in Java are true?

Accepted Answer

A final variable cannot be reassigned after initialization.. A final variable in Java can only be assigned once. After initialization, any attempt to reassign the variable results in a compile-time error. This ensures the variable's value remains constant throughout its scope.

Answer

A final method can be overridden in a subclass.

Answer

A final parameter in a method allows the method to modify the argument value.