1Z0-811 Practice Test 12 — 15 Questions

Question 1

Which two control flow statements can be used to terminate a loop prematurely?

Accepted Answer

return. Options A (return) and D (break) are correct. The return statement terminates the enclosing method, thereby ending the loop. The break statement directly terminates the innermost loop. Option B (exit) is not a Java statement; System.exit() is a method but it is not a control flow statement for loop termination. Option C (System.gc()) is a garbage collection hint and does not affect loop control. Option E (continue) skips the current iteration but does not terminate the loop.

Answer

exit

Answer

System.gc()

Answer

continue

Question 2

A method 'public static int findMax(int[] numbers)' returns the maximum value in the array. Which implementation correctly handles an empty array by returning 0?

Accepted Answer

if(numbers.length == 0) return 0; int max = numbers[0]; for(int i=1; i<numbers.length; i++) if(numbers[i] > max) max = numbers[i]; return max;. Ly handles an empty array by checking `numbers.length == 0` and returning 0 before attempting to access `numbers[0]`, which would throw an `ArrayIndexOutOfBoundsException` on an empty array. It then initializes `max` to the first element and iterates from index 1, ensuring all elements are compared correctly even if all numbers are negative.

Answer

int max = 0; for(int n: numbers) if(n > max) max = n; return max;

Answer

int max = numbers[0]; for(int i=1; i<numbers.length; i++) if(numbers[i] > max) max = numbers[i]; return max;

Answer

if(numbers.length == 0) return 0; int max = 0; for(int n: numbers) if(n > max) max = n; return max;

Question 3

What is the result of: Integer a = null; int b = (a != null) ? a : 0; System.out.println(b);

Accepted Answer

0. The ternary operator evaluates the condition (a != null). Since a is null, the condition is false, so the expression returns the second operand, which is the int literal 0. This value is assigned to int b, and System.out.println(b) prints 0. No NullPointerException occurs because the ternary operator never attempts to unbox a null reference.

Answer

NullPointerException

Answer

Compilation error

Answer

null

Question 4

A class defines a static variable initialized at declaration: static int count = 10;. A static method attempts to modify it: count = 20;. Which statement is true?

Accepted Answer

The variable can be changed to 20. Static variables belong to the class, not instances, and can be accessed and modified by static methods. The assignment `count = 20;` is valid and changes the value from 10 to 20 at runtime.

Answer

The variable cannot be accessed from a static method

Answer

The code causes a compilation error

Answer

The variable is read-only

Question 5

A developer writes: if (x = 5) { System.out.println("x is 5"); } What is the result?

Accepted Answer

Compilation error. In Java, the assignment operator `=` is used for assignment, not comparison. The expression `x = 5` assigns the value 5 to variable `x` and returns the assigned value (5). Since the condition in an `if` statement must be a boolean expression, and `int` cannot be implicitly converted to `boolean`, the compiler throws a compilation error. This is a fundamental syntax rule in Java, unlike in C/C++ where such an assignment would be allowed as a truthy check.

Answer

Prints "x is 5" if x equals 5

Answer

No output

Answer

Prints "x is 5" always

Question 6

Which TWO are valid ways to handle a checked exception in a method?

Accepted Answer

Catch the exception within the method. Catching a checked exception within the method using a try-catch block is a valid way to handle it. The Java compiler enforces that checked exceptions (subclasses of Exception but not RuntimeException) must be either caught or declared, so catching the exception satisfies the compiler's requirement.

Answer

Ignore the exception by doing nothing

Answer

Use assert to suppress the exception

Answer

Convert it to a runtime exception by throwing a new RuntimeException

Question 7

Refer to the exhibit. What is the likely cause of this error?

Accepted Answer

x is declared but not initialized. In Java, a local variable must be explicitly initialized before it is used; otherwise, the compiler reports an 'error: variable x might not have been initialized'. The exhibit shows a compilation error, and the most likely cause is that x was declared (e.g., 'int x;') but never assigned a value before being referenced in an expression or printed.

Answer

x is out of scope

Answer

x is a duplicate variable

Answer

x is declared as a different type

Question 8

Refer to the exhibit. Which overloaded methods cause this compilation error?

Accepted Answer

public void print(String[] s) and public void print(String... s). Java does not allow overloading methods that differ only by the use of a varargs parameter and an array parameter of the same type. Both `public void print(String[] s)` and `public void print(String... s)` have the same method signature after erasure — they both accept a `String[]` at the bytecode level — causing a compilation error due to ambiguity.

Answer

public void print(String s) and public void print(String[] s)

Answer

public void print(String s) and public void print(String... s)

Answer

public void print(Object... o) and public void print(String... s)

Question 9

A novice developer wrote a condition: if (x = 10) { ... } What is the result?

Accepted Answer

Compilation error. In Java, the assignment operator `=` is used to assign a value, not to compare values. The condition `if (x = 10)` attempts to assign 10 to `x` within an `if` statement, which is not a boolean expression. Java requires the condition in an `if` statement to evaluate to a `boolean`, so this code will not compile. Option D is correct because the compiler will report an error, typically stating 'incompatible types: int cannot be converted to boolean'.

Answer

The condition always evaluates to true

Answer

It executes the block if x equals 10

Answer

Runtime exception thrown

Question 10

You are developing a Java application for a library management system. The system must track the number of books in each genre. You need to store genre names (String) and their counts (int). The data will be accessed frequently and modified rarely. Which Java data structure should you use to store this mapping efficiently, while ensuring that genre names are unique?

Accepted Answer

HashMap. HashMap is the correct choice because it stores key-value pairs, where each genre name (String) is a unique key mapped to its count (Integer). This provides O(1) average-time complexity for lookups and updates, which is ideal for frequent access and rare modifications. The HashMap ensures key uniqueness via its hash-based implementation, directly meeting the requirement of unique genre names.

Answer

ArrayList<Book>

Answer

LinkedList<String>

Answer

HashSet<String>

Question 11

A developer writes a loop that iterates over an array of integers. The loop should stop when it encounters a negative number. Which control flow construct best achieves this?

Accepted Answer

for loop with break inside if condition. A for loop with a break statement allows the developer to iterate over an array of integers and immediately exit the loop when a negative number is encountered. The break statement terminates the loop's execution unconditionally, making it the most direct and readable control flow construct for this requirement.

Answer

do-while loop

Answer

enhanced for loop with return

Answer

while loop with continue

Question 12

Given: String s = "Java"; s.concat(" Rocks"); System.out.println(s); What prints?

Accepted Answer

"Java". Strings in Java are immutable. The `concat()` method returns a new string object but does not modify the original string `s`. Since the return value is not assigned to any variable, the original string `s` remains unchanged, so `System.out.println(s)` prints "Java".

Answer

"Rocks"

Answer

""

Answer

"Java Rocks"

Question 13

A team is designing a library that handles network timeouts. They create a custom exception `NetworkTimeoutException` that extends `Exception`. They want to ensure that callers are forced to handle this exception. Which declaration is appropriate for a method that throws this exception?

Accepted Answer

public void connect() throws NetworkTimeoutException. The method must declare the custom checked exception `NetworkTimeoutException` in its throws clause to force callers to handle it. Since `NetworkTimeoutException` extends `Exception` (not `RuntimeException`), it is a checked exception, and the Java compiler enforces that any method throwing it must declare it with the `throws` keyword followed by the exception type name.

Answer

public void connect() throws RuntimeException

Answer

public void connect() throws e where e is NetworkTimeoutException

Answer

public void connect() throw NetworkTimeoutException

Question 14

Which method invocation is ambiguous given these overloaded methods? public void process(int[] a) and public void process(int... a)

Accepted Answer

process(new int[]{1, 2});. When you call process(new int[]{1, 2}), the compiler cannot determine whether to use the method with an int[] parameter or the varargs method (int... a). Both methods have the same signature after type erasure, and the argument is an int array, which matches both exactly, causing an ambiguity error.

Answer

process(1, 2);

Answer

process((int[]) null);

Answer

process();

Question 15

Which primitive type can store a single character?

Accepted Answer

char. The `char` primitive type in Java is specifically designed to store a single 16-bit Unicode character, ranging from '\u0000' (0) to '\uffff' (65535). It is the only primitive type that directly represents a character value, making it the appropriate choice for storing a single character.

Answer

String

Answer

byte

Answer

short