1Z0-811 Practice Test 7 — 10 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"