1Z0-811 Practice Test 18 — 15 Questions

Question 1

What is the output of System.out.println(1 + 2 + "3" + 4 + 5);?

Accepted Answer

3345. Java evaluates the expression left-to-right. The first operation is `1 + 2`, which is integer addition, yielding `3`. Then `3 + "3"` triggers string concatenation, producing `"33"`. The remaining `+ 4` and `+ 5` are also string concatenations, appending `"4"` and `"5"` to give `"3345"`. The `println` method outputs this string.

Answer

12345

Answer

3"3"45

Answer

15

Question 2

A junior developer writes a simple 'Hello World' program and saves it as HelloWorld.java. He compiles it successfully with 'javac HelloWorld.java', confirming that HelloWorld.class is created in the current directory. When he tries to run it with the command 'java HelloWorld', the system returns 'Error: Could not find or load main class HelloWorld'. The current directory is indeed the one containing HelloWorld.class. He has JAVA_HOME set to the JDK installation directory and has verified that java is in the PATH. What is the most likely cause?

Accepted Answer

The classpath does not include the current directory. By default, the java command does not include the current directory in the classpath, so even though HelloWorld.class exists in the current directory, the JVM cannot find it. The developer must explicitly add the current directory using -cp . or set the CLASSPATH environment variable. Option A is incorrect because a corrupt class file would typically cause a ClassFormatError, not 'Could not find or load main class'. Option C is incorrect because a missing or incorrect main method would yield 'Main method not found in class HelloWorld' error. Option D is incorrect because the error message indicates that the java command executed (it found the java executable), so it is in the PATH.

Answer

The class file is corrupt

Answer

The main method is missing or incorrectly declared

Answer

The java command is not in the PATH

Question 3

Which three of the following statements about primitive type conversion are true?

Accepted Answer

Implicit widening conversion is allowed from int to long.. The correct answers are B, D, and E. 
- B is correct: Implicit widening conversion from int to long is allowed because long has a larger range (64-bit vs 32-bit). 
- D is correct: A char can be assigned to an int without a cast because char is 16-bit unsigned and int is 32-bit, so the value fits without loss. 
- E is correct: Narrowing conversion from double to int requires an explicit cast because double has a larger range and fractional part cannot be automatically discarded. 
- A is false: A float cannot be implicitly converted to long because float is 32-bit floating-point; conversion would lose precision and requires an explicit cast. 
- C is false: A boolean cannot be converted to any numeric type, even with casting; boolean and numeric types are incompatible.

Answer

A float can be implicitly converted to long.

Answer

A boolean can be converted to int using casting.

Question 4

Which TWO of the following operations on String objects result in a new String object?

Accepted Answer

"Hello".replace('l', 'p'). `String.replace()` returns a new `String` object with the replacement applied, as `String` is immutable in Java. The original `"Hello"` remains unchanged, and a new string `"Heppo"` is created.

Answer

"Hello".toString()

Answer

"Hello".length()

Answer

"Hello".charAt(0)

Question 5

Which TWO are valid ways to pass an array to a method in Java?

Accepted Answer

myMethod(new int[]{1,2,3});. `new int[]{1,2,3}` is an anonymous array creation expression that creates a new int array and passes it directly to the method. This syntax is valid in Java for passing an array literal without a variable. Option B is correct because it declares an array variable `arr` initialized with an array initializer `{1,2,3}` (which is allowed only in a declaration statement) and then passes that reference to the method, which is a standard way to pass an array.

Answer

myMethod(1, 2, 3);

Answer

myMethod(int[] {1,2,3});

Answer

myMethod(new int[5] {1,2,3,4,5});

Question 6

Consider the following code:
```java
import java.io.*;

public class Test {
    public static void main(String[] args) throws IOException {
        try (FileInputStream fis = new FileInputStream("test.txt");
             BufferedReader br = new BufferedReader(new InputStreamReader(fis))) {
            System.out.println(br.readLine());
        } catch (IOException e) {
            System.out.println("Error");
        }
    }
}
```
Which statement about this code is true?

Accepted Answer

The catch block is unnecessary.. The code likely uses a try-with-resources statement, which automatically closes resources. The catch block is unnecessary since the resources are closed automatically, and the exception can be declared to be thrown. The code compiles without the catch block, and resource management is handled by the try-with-resources construct.

Answer

The resource 'br' is not closed properly.

Answer

The code will not compile because of the throws clause.

Answer

The resource 'fis' is closed before 'br'.

Question 7

int count = 0;
for (int i = 0; i < 5; i++) {
    if (i == 2) {
        continue;
    }
    count++;
}
System.out.println(count);

What is the output of the program?

Accepted Answer

4. The loop iterates from i=0 to i=4. When i equals 2, the continue statement skips the rest of the loop body, so the increment of count is not executed for i=2. For the remaining four iterations (i=0,1,3,4), count is incremented, resulting in a final value of 4. Option B is incorrect because the loop code is syntactically valid and compiles without error. Option C would be correct if a break statement were used instead of continue. Option D is incorrect because the loop runs the full 5 iterations, incrementing count 4 times.

Answer

The loop does not compile.

Answer

5

Answer

2

Question 8

The code does not compile. What is the error?

Accepted Answer

Assignment instead of comparison in if condition. The code uses a single equals sign `=` (assignment) inside the `if` condition instead of `==` (comparison). In Java, `if (x = 5)` assigns the value 5 to `x` and then evaluates the assignment expression to the assigned value (5), which is an `int`, not a `boolean`. The `if` statement requires a `boolean` expression, so this causes a compilation error.

Answer

Missing semicolon after if condition

Answer

Variable x is not initialized

Answer

System.out.println syntax error

Question 9

Given the compilation error above, which fix would resolve the error?

Accepted Answer

Wrap the code in a try-catch block for FileNotFoundException.. The compilation error indicates that the code uses a constructor or method that throws a checked `FileNotFoundException` (a subclass of `IOException`). In Java, checked exceptions must be either caught with a try-catch block or declared in the method signature. Wrapping the code in a try-catch block for `FileNotFoundException` handles the exception locally, resolving the compilation error without altering the method signature.

Answer

Add a throws FileNotFoundException clause to the main method.

Answer

Change FileReader to BufferedReader.

Answer

Use FileInputStream instead.

Question 10

A developer is writing a method to find the first occurrence of a negative number in an array and return its index, or -1 if none found. The current implementation uses a for loop with an if condition and a return when found. However, the method throws a NullPointerException when the array is null. The developer wants to handle this edge case gracefully and still return -1. Which approach is most appropriate?

Accepted Answer

Add a null check at the beginning of the method and return -1 if null. It directly checks if the array reference is null before any iteration, returning -1 immediately. This is the simplest and most efficient way to handle a null input, avoiding any attempt to access the array's length or elements, which would throw a NullPointerException. The method's contract is preserved by returning -1 when no negative number is found, including the case of a null array.

Answer

Use an enhanced for loop with a null check

Answer

Use a try-catch block inside the loop

Answer

Use a while loop with a null check inside

Question 11

A developer needs to search an unsorted array of 100,000 customer IDs (int) for a specific ID. Which approach is most efficient for a single search?

Accepted Answer

Iterate through the array and compare each element. A linear search (iterating through the array and comparing each element) is the most efficient approach for a single search on an unsorted array. It has O(n) time complexity and requires no preprocessing, which is optimal when you only need to find one element once.

Answer

Use Arrays.binarySearch() directly on the unsorted array

Answer

First sort the array using Arrays.sort(), then use binary search

Answer

Convert the array to a HashSet and then search

Question 12

Refer to the exhibit. What is the output?

Accepted Answer

2. The code initializes an array `arr` with values {1, 2, 3}. The for loop iterates over the array, and the `if` condition checks if the current element equals 2. When `arr[1]` (value 2) is encountered, the `break` statement exits the loop immediately. The loop executes only twice (for indices 0 and 1), so the counter `count` is incremented twice, resulting in output 2.

Answer

3

Answer

1

Answer

0

Question 13

A team is implementing a search algorithm that iterates over an array of integers. The loop should stop as soon as the target value is found. Which loop construct is most appropriate?

Accepted Answer

For loop with break. The most appropriate loop construct for this scenario is a for loop with a break statement. A for loop provides a concise way to iterate over an array by index, and the break statement allows the loop to terminate immediately once the target value is found, avoiding unnecessary iterations. While a while loop with a flag variable could also work, the for loop is more idiomatic and less error-prone. An enhanced for loop supports break as well, but it lacks access to the loop index, which may be needed. A do-while loop is not suitable because it guarantees at least one iteration even if the array is empty or the target is found early. Therefore, option D is correct.

Answer

While loop with a flag variable

Answer

Enhanced for loop with continue

Answer

Do-while loop

Question 14

A junior developer wrote the following code to calculate the sum of an array:

int[] numbers = {1, 2, 3, 4, 5};
int sum = 0;
for (int i = 1; i <= numbers.length; i++) {
    sum += numbers[i];
}
System.out.println("Sum: " + sum);

The developer expects the output to be 15, but the program throws an exception. What is the root cause and the correct fix?

Accepted Answer

Change to: for (int i = 0; i < numbers.length; i++). The loop starts at index 1 instead of 0, and goes up to index numbers.length (which is 5), but valid indices are 0-4. So accessing numbers[5] throws ArrayIndexOutOfBoundsException. The correct fix is to start at i=0 and continue while i < numbers.length, which is option B. Option A uses an enhanced for loop, which is also a valid fix but changes the loop style; however, the question asks for the root cause and correct fix, and option B directly corrects the indexing. Option C changes the step to 2 and starts at 1, still wrong. Option D uses i <= numbers.length, which still causes out-of-bounds.

Answer

Change to enhanced for loop: for (int num : numbers) sum += num;

Answer

Change to: for (int i = 1; i < numbers.length; i += 2)

Answer

Change to: for (int i = 0; i <= numbers.length; i++)