1Z0-811 Practice Test 27 — 15 Questions

Question 1

A company's application uses a switch statement to handle different user roles. The code currently has a bug where after processing one role, it unintentionally executes the next role's logic. Which concept is being misused?

Choose an answer to begin — your selection is scored in the full session.

Accepted Answer

Missing break statements causing fall-through. In Java, a switch statement without break statements causes fall-through, where execution continues into subsequent case blocks even after a match is found. This is exactly the bug described: after processing one role, the code unintentionally executes the next role's logic because no break terminates the case.

Answer

Incorrect default case

Answer

Using enum in switch

Answer

Using string in switch (Java 7+)

Question 2

What is the value of y after executing the following code?
```java
int y = 10 + 12;
```

Accepted Answer

22. The code snippet `int y = 10 + 12;` performs integer addition, resulting in y = 22. Java's primitive arithmetic follows standard rules, so adding 10 and 12 yields 22 without any overflow or conversion issues.

Answer

20

Answer

21

Answer

23

Question 3

A method returns a String. The team debates using == vs equals(). Which correctly describes String comparison in Java?

Accepted Answer

== may return true for two different references if they point to the same interned string.. The == operator in Java compares object references, not content. However, due to string interning, two different String variables that reference the same interned string literal will have the same memory reference, causing == to return true. This is a special case that can mislead developers into thinking == compares content.

Answer

== compares the content of two Strings.

Answer

== always returns false for different String objects, even if content is same.

Answer

equals() compares the memory addresses.

Question 4

A developer needs to concatenate several string values in a loop. Which approach is most efficient for performance?

Accepted Answer

Using StringBuilder. StringBuilder is the most efficient approach for concatenating strings in a loop because it maintains a mutable sequence of characters, avoiding the creation of intermediate String objects. In contrast, using the '+' operator or String.concat() inside a loop results in the allocation of a new String object for each concatenation, leading to O(n²) time complexity and increased garbage collection overhead.

Answer

Using String.concat()

Answer

Using the '+' operator inside the loop

Answer

Using StringBuffer

Question 5

Which TWO are valid identifiers in Java? (Choose two.)

Accepted Answer

$money. In Java, identifiers can begin with a letter, an underscore (_), or a dollar sign ($). The dollar sign is a valid starting character, so '$money' is a legal identifier. This is specified in the Java Language Specification (JLS §3.8).

Answer

123abc

Answer

2ndPlace

Answer

my-var

Question 6

Given the following try-catch block:
try {
    // some code
} catch (IOException | NumberFormatException e) {
    e = new IOException("wrapper");
    // throw e;
}
Which line causes a compilation error?

Accepted Answer

The assignment to e. In a multi-catch block, the exception parameter `e` is implicitly `final` and cannot be reassigned. The assignment `e = new IOException("wrapper")` violates this rule, causing a compilation error at that line.

Answer

The multi-catch syntax

Answer

No error

Answer

The throw statement

Question 7

Which of the following is the best practice for resource management in Java?

Accepted Answer

Use try-with-resources statement.. The try-with-resources statement (introduced in Java 7) automatically closes each resource declared in its header when the block exits, whether normally or due to an exception. This eliminates the need for explicit cleanup code and ensures that resources implementing `AutoCloseable` are closed reliably, preventing resource leaks.

Answer

Close resources in a finally block without null checks.

Answer

Rely on garbage collection to close resources.

Answer

Use a try-catch block and close resources in the catch block.

Question 8

Which command is used to run a Java application from the command line?

Accepted Answer

java. The `java` command is the correct tool to launch a Java application from the command line. It invokes the Java Virtual Machine (JVM) to load and execute the compiled bytecode contained in `.class` files or a JAR file. Without this command, the application cannot run.

Answer

jar

Answer

javac

Answer

javadoc

Question 9

A developer wants to prevent a method from being overridden. Which modifier should be used?

Accepted Answer

final. The `final` modifier prevents a method from being overridden in a subclass. When a method is declared as `final`, any attempt to override it in a subclass results in a compile-time error, ensuring the method's implementation remains unchanged.

Answer

private

Answer

abstract

Answer

static

Question 10

You are writing a program that processes a list of transactions. Each transaction has a timestamp (long), amount (double), and type (String). The program needs to iterate through the transactions in the order they were added. Which collection should you use to maintain insertion order and allow fast iteration?

Accepted Answer

ArrayList<Transaction>. ArrayList maintains insertion order and provides O(1) random access and fast iteration via index-based traversal. It is the correct choice when you need to preserve the order in which elements were added and iterate over them sequentially without requiring sorting or unique constraints.

Answer

TreeSet<Transaction>

Answer

LinkedList<Transaction>

Answer

HashSet<Transaction>

Question 11

Which THREE are valid Java identifiers? (Choose three.)

Accepted Answer

$dollar. Option A ($dollar) is a valid Java identifier because the dollar sign ($) is a legal identifier-start character in Java, alongside letters, the underscore, and Unicode currency symbols. Option D (_value) is valid because an underscore is a legal identifier-start character, so a name beginning with _ followed by letters is accepted by the compiler. Option E (myVar123) is valid because it starts with a letter and continues with letters and digits, and digits are permitted in identifiers as long as they are not the first character. Option B (my var) is invalid because it contains a space, which is not a legal identifier character and would be parsed as two separate tokens. Option C (2ndValue) is invalid because it begins with the digit 2, and Java identifiers cannot start with a numeric digit.

Answer

my var

Answer

2ndValue

Question 12

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 13

Which data type should be used to store a single character like 'A'?

Accepted Answer

char. In Java, the `char` data type is a single 16-bit Unicode character, capable of storing any character from the Unicode standard, including 'A'. It is the primitive type specifically designed for a single character, whereas `String` is a reference type for sequences of characters.

Answer

String

Answer

byte

Answer

int

Question 14

What does the java command with -jar option do?

Accepted Answer

Executes a JAR file by reading its manifest. The `java -jar` command executes a JAR file by reading the `Main-Class` entry from the JAR's manifest file (`META-INF/MANIFEST.MF`). This tells the Java launcher which class contains the `public static void main(String[] args)` method to start the application. It does not compile, list, or create JAR files.

Answer

Compiles Java files inside the JAR

Answer

Lists contents of the JAR file

Answer

Creates a new JAR file

Question 15

A developer writes two methods: public void process(int a) { ... } and public void process(double a) { ... }. Which method is called by process(10)?

Accepted Answer

The method with int parameter. Java selects the most specific overloaded method at compile time. When calling process(10), the integer literal 10 is an int, so the compiler prefers the method with the int parameter over the double parameter, as no implicit widening conversion is required.

Answer

The method with double parameter

Answer

Compilation error: ambiguous call

Answer

Runtime error: NoSuchMethod