1Z0-811 Practice Test 3 — 30 Questions

Question 1

Which THREE are benefits of Java's platform independence? (Choose three.)

Accepted Answer

Ability to run on any device with a JVM. Option A is correct because Java source is compiled to bytecode that executes on the Java Virtual Machine, so any device providing a compatible JVM can run the same class files regardless of underlying OS or CPU architecture. Option B is correct because this portability is precisely the 'write once, run anywhere' (WORA) promise: a single compiled artifact is not recompiled per platform, only interpreted/JIT-compiled by the local JVM. Option E is correct because the JVM's class loader, bytecode verifier, and SecurityManager architecture provide a sandbox that constrains untrusted code, a security benefit tied to running on the managed JVM layer. Option C is not a benefit of platform independence—bytecode is typically interpreted or JIT-compiled and generally slower to warm up than optimized native code, so it is not a portability advantage. Option D is a feature of the Java runtime (garbage collection) but is unrelated to platform independence, so it does not belong.

Answer

Faster execution compared to native code

Answer

Automatic memory management

Question 2

A developer needs to iterate over an array of integers and compute the sum of its elements. Which loop construct is most appropriate for this task?

Accepted Answer

Enhanced for loop. The enhanced for loop (for-each) is the most appropriate construct for iterating over an array of integers to compute a sum because it provides a concise, read-only traversal without needing an explicit index or iterator. It directly accesses each element in sequence, reducing boilerplate and the risk of off-by-one errors, which is ideal for aggregation operations like summation.

Answer

while loop

Answer

switch statement

Answer

do-while loop

Question 3

Given the code:

int[] a = {1, 2, 3};
int[] b = {4, 5};
a = b;
b[0] = 99;
System.out.println(a[0]);

What is the output?

Accepted Answer

99. After `a = b;`, both `a` and `b` reference the same array object. Modifying `b[0]` to 99 also changes `a[0]` because they share the same underlying array. Therefore, `a[0]` prints 99.

Answer

3

Answer

1

Answer

4

Question 4

What is the value of the expression: 2 + 3 * 4 / 2 - 1?

Accepted Answer

7. In Java, the expression 2 + 3 * 4 / 2 - 1 is evaluated according to operator precedence: multiplication (*) and division (/) have higher precedence than addition (+) and subtraction (-), and they associate left-to-right. So 3 * 4 = 12, then 12 / 2 = 6 (integer division). The expression becomes 2 + 6 - 1, which is evaluated left-to-right: 2 + 6 = 8, then 8 - 1 = 7. Thus the correct answer is 7.

Answer

9

Answer

10

Answer

3

Question 5

In a banking application, a class 'Account' has a private field 'balance'. Which is the best way to allow subclasses to read but not directly modify 'balance'?

Accepted Answer

Provide a public getBalance() method. It follows encapsulation: a public getBalance() method provides read-only access to the private balance field. Subclasses cannot directly modify balance because it is private. Option D (protected) is incorrect because protected access allows subclasses to directly read and write the field, which violates the requirement that subclasses should not be able to directly modify balance.

Answer

Make balance public

Answer

Use a static variable

Answer

Make balance protected

Question 6

Arrange the steps to use a for loop to iterate over an array in Java in the correct order.

Accepted Answer

1. Declare and initialize the array. 2. Write a for loop with initialization, condition, and increment statements. 3. Access elements using array[index] inside the loop. 4. Execute desired operations on each element.. First set up the array, then write a for loop with proper syntax, access elements using index, execute body, and consider enhanced for.

Answer

1. Write a for loop header with initialization, condition, and increment. 2. Declare and initialize the array inside the loop. 3. Access elements using array[index]. 4. Perform operations.

Answer

1. Access array elements using index. 2. Declare and initialize the array. 3. Write a for loop to iterate. 4. Perform operations.

Answer

1. Declare and initialize the array. 2. Perform operations on array elements without a loop. 3. Write a for loop later. 4. Access elements using index.

Question 7

A developer implements a method to check if a number exists in an array using binary search. The array is not sorted. What will happen?

Accepted Answer

The method returns incorrect results sometimes.. Binary search requires the array to be sorted to work correctly. If the array is not sorted, the algorithm may skip over the target element or incorrectly conclude it is absent, leading to incorrect results. Therefore, the method returns incorrect results sometimes.

Answer

The method returns correct results always.

Answer

Runtime exception.

Answer

Compilation error.

Question 8

Which THREE statements about custom exceptions in Java are correct? (Select exactly 3)

Accepted Answer

A checked custom exception must be declared in the throws clause of any method that throws it.. Option A is correct because a checked exception (any subclass of Exception that is not a subclass of RuntimeException) is subject to the Java checked-exception rule, so any method that throws it must declare it in its throws clause or the code will not compile. Option B is correct because a custom exception can be designed as either checked (extending Exception) or unchecked (extending RuntimeException), giving the developer control over whether callers are forced to handle it. Option C is correct because the defining characteristic of an unchecked exception in Java is that it extends RuntimeException (or one of its subclasses), so an unchecked custom exception must extend RuntimeException. Option D is incorrect because a custom exception need not extend Throwable directly; it typically extends Exception or RuntimeException, which already inherit from Throwable. Option E is incorrect because custom exceptions can and commonly do define constructors that call super(...) to pass messages or causes to the parent class.

Answer

A custom exception class must directly extend Throwable.

Answer

A custom exception cannot have constructors that call super.

Question 9

A developer is debugging a Java application that throws a NullPointerException. Which two actions help identify the source of the exception? (Choose two.)

Accepted Answer

Use a debugger to step through code. Option B is correct because a debugger lets you set breakpoints and step through the code line by line, inspecting variable values and the call stack at the exact moment the NullPointerException is thrown, which pinpoints the null reference. Option C is correct because the stack trace printed when a NullPointerException is thrown shows the exact class, method, file, and line number where the null dereference occurred, immediately identifying the source. Option A is not ideal because println statements only show whatever you explicitly print and do not reveal the exception's origin or call path. Option D is wrong because the -g flag only adds debugging symbols (line numbers, local variable info) to the compiled class files; it does not itself identify where the exception came from. Option E is insufficient because catching the exception and printing only its message typically yields just 'null' without the stack trace, so the source location remains unknown.

Answer

Use System.out.println statements

Answer

Recompile with -g flag

Answer

Catch the exception and print its message

Question 10

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 11

Which is the correct way to call a superclass constructor from a subclass constructor?

Accepted Answer

super(); as first statement. In Java, a call to the superclass constructor using `super()` must be the first statement in a subclass constructor. This ensures that the superclass initialization completes before any subclass-specific code executes, maintaining the inheritance chain. Option B correctly identifies this requirement.

Answer

super(); anywhere

Answer

super(); at the end

Answer

this.super();

Question 12

A developer says Java is platform-independent because of the JVM. Which statement best explains this?

Accepted Answer

Java source code is compiled into bytecode, which runs on the Java Virtual Machine (JVM).. Java achieves platform independence through a two-step compilation model: javac compiles source code into platform-neutral bytecode (.class files), and the JVM on each platform interprets or JIT-compiles that bytecode into native instructions. Because the bytecode is the same everywhere and only the JVM is platform-specific, the same compiled artifact runs on Windows, Linux, or macOS without recompilation.

Answer

Java source code is compiled directly into native machine code for each platform.

Answer

The JVM is written in platform-independent code, allowing it to run anywhere.

Answer

Java uses an interpreter only, so the source code is interpreted directly on any platform.

Question 13

Which TWO keywords are used to control access to class members? (Choose two.)

Accepted Answer

private. The question asks for keywords that control access to class members, i.e., access modifiers. Option A, private, is correct because it restricts a member's visibility to the declaring class only, preventing access from subclasses or other classes. Option C, public, is correct because it grants unrestricted access to a member from any other class in any package. The other options do not control access: static (B) controls whether a member belongs to the class rather than instances, abstract (D) declares that a method has no implementation or that a class cannot be instantiated, and final (E) prevents reassignment, overriding, or inheritance.

Answer

static

Answer

abstract

Answer

final

Question 14

Given: int day = 3; switch(day) { case 1: System.out.print("A"); case 2: System.out.print("B"); case 3: System.out.print("C"); case 4: System.out.print("D"); } What prints?

Accepted Answer

"CD". The switch statement does not have break statements, so after matching case 3, execution falls through to case 4, printing 'C' then 'D'. The output is 'CD'.

Answer

"BCD"

Answer

"C"

Answer

"ABCD"

Question 15

A developer writes a class 'Animal' with a method 'sound()'. The 'Cat' subclass overrides 'sound()'. If an Animal reference points to a Cat object, which method is called when sound() is invoked?

Accepted Answer

Cat's sound(). Java uses dynamic (runtime) method dispatch for overridden instance methods. When an Animal reference points to a Cat object and sound() is invoked, the JVM looks up the actual object type (Cat) and calls Cat's overridden sound() method. This is the essence of polymorphism in Java.

Answer

Runtime error

Answer

Animal's sound()

Answer

Compilation error

Question 16

You are part of a team maintaining a legacy order processing system. The system stores order totals as primitive double values. A recent bug report shows that for very large orders (around $1,000,000.00), the total after adding a tax of 8.25% is sometimes off by a few cents. The calculation is: total = orderTotal * (1 + taxRate). The taxRate is defined as double taxRate = 0.0825; The orderTotal is received as a double. The application needs exact monetary precision to two decimal places. Which solution best addresses the precision issue while minimizing changes to the existing code?

Accepted Answer

Use BigDecimal for all monetary calculations, replacing double everywhere.. double is a binary floating-point type (IEEE 754) and cannot represent most decimal fractions exactly — 0.0825 and the resulting products accumulate rounding error that surfaces as cent-level discrepancies at large magnitudes. BigDecimal uses arbitrary-precision decimal arithmetic with explicit scale and RoundingMode, giving exact monetary results. Replacing double with BigDecimal for monetary fields is the only option that fixes the root cause rather than masking it.

Answer

Use DecimalFormat with RoundingMode.HALF_EVEN to format the output.

Answer

Use Math.round(total * 100) / 100.0 to round to two decimals.

Answer

Cast the result to float and then back to double to round.

Question 17

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

Accepted Answer

"Hello".replace('l', 'p'). Option D, "Hello".replace('l', 'p'), is correct because String is immutable and replace() returns a brand-new String ("Heppo") rather than modifying the original instance. Option E, "Hello".concat(" World"), is also correct because concat() returns a new String ("Hello World") formed by appending the argument to the original, again leaving the original unchanged. Option A, "Hello".toString(), is not correct because toString() on a String simply returns this, the same existing String reference, not a new object. Option B, "Hello".length(), is not correct because it returns an int primitive (5), not a String object. Option C, "Hello".charAt(0), is not correct because it returns a char primitive ('H'), not a String object.

Answer

"Hello".toString()

Answer

"Hello".length()

Answer

"Hello".charAt(0)

Question 18

Given: String s1 = "Java"; String s2 = new String("Java"); What does (s1 == s2) evaluate to?

Accepted Answer

false. The == operator on object references checks identity, not content. s1 is a literal in the string constant pool, while s2 is a new String object on the heap, so they are different objects and (s1 == s2) is false. The intern() method is not called, so the pool reference is not shared.

Answer

true if interned, false otherwise

Answer

true

Answer

Compilation error

Question 19

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 i = 1 and runs while i <= numbers.length, so when i equals numbers.length (5), it accesses numbers[5], which is out of bounds for a 5-element array (valid indices 0–4), causing an ArrayIndexOutOfBoundsException. The correct fix is to start at i = 0 and use i < numbers.length to iterate all elements exactly once.

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++)

Question 20

Which TWO of the following development tools are specifically designed to analyze module dependencies or create custom runtime images?

Accepted Answer

jdeps. jdeps (A) is correct because it is the Java Dependency Analysis Tool that inspects class files and JARs to report package-level and module-level dependencies, including identifying required modules and internal APIs. jlink (B) is correct because it is the Java Linker tool that assembles a custom runtime image from a set of modules, using the module graph to include only the needed JDK modules. The other options do not fit: jar (C) packages class files and resources into an archive but does not analyze module dependencies or build runtime images; javadoc (D) generates API documentation from source comments; and javac (E) compiles Java source code into bytecode.

Answer

jar

Answer

javadoc

Answer

javac