1Z0-811 Practice Test 34 — 15 Questions

Question 1

A payroll system stores weekly hours in an int array. A developer writes a method that should double every element in the array and return the sum of the modified values. The method signature is public static int process(int[] hours). Inside the method, the developer uses a for-each loop: for (int h : hours) { h = h * 2; } and then sums the elements. What is the result when the method is called with an array containing {1, 2, 3}?

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

Accepted Answer

The method returns 6, and the original array remains {1, 2, 3}.. A for-each loop over a primitive array assigns each element to a local variable; reassigning that variable does not affect the array. The method sums the original values, producing 6, and the caller's array stays {1, 2, 3}. To double elements, the method would need an indexed for loop and assign hours[i] = hours[i] * 2.

Answer

The method returns 12, and the original array remains {1, 2, 3}.

Answer

The method returns 6, and the original array becomes {1, 2, 3} only if the array is passed by reference.

Answer

The method returns 12, and the original array becomes {2, 4, 6}.

Question 2

A developer writes a method that accepts a two-dimensional int array representing a grid of scores and returns the sum of all elements. Which construct correctly visits every element in every row?

Accepted Answer

Nested for loops, the outer bounded by grid.length and the inner by grid[i].length. A two-dimensional array in Java is an array of arrays, so complete traversal requires two loops. The outer loop iterates over rows using the top-level length, and the inner loop iterates over the columns of the currently selected row using that row's own length. This pairing correctly accumulates every element and remains safe for jagged arrays.

Answer

A while loop that increments a counter until it equals grid[0].length

Answer

A single for loop using grid.length as the bound and indexing grid[i]

Answer

Nested for loops, both bounded by grid.length

Question 3

A developer defines an abstract class named Vehicle with an abstract method move and a concrete method describe. A class named Bicycle extends Vehicle but does not implement move. What is the result when the developer attempts to compile Bicycle?

Accepted Answer

Compilation fails because Bicycle must implement move or be declared abstract.. An abstract class can declare abstract methods that subclasses must implement. Any concrete subclass must provide bodies for all inherited abstract methods. Bicycle neither implements move nor is declared abstract, so compilation fails. Abstract classes may also contain concrete methods, so the presence of describe is not the issue.

Answer

Compilation fails because abstract classes cannot contain concrete methods.

Answer

Compilation succeeds, but a runtime exception is thrown when Bicycle is instantiated.

Answer

Compilation succeeds because Vehicle already provides a default implementation of move.

Question 4

A junior developer asks how Java achieves platform independence. Which statement best describes the role of the Java Virtual Machine (JVM) in this process?

Accepted Answer

The JVM executes Java bytecode, which is the same regardless of the underlying operating system, allowing the same compiled program to run on different platforms.. Java compiles source code to bytecode, a platform-independent intermediate representation. Each platform has a JVM that can execute that bytecode, either by interpreting it or by compiling it to native code at runtime. This architecture lets the same compiled class files run on Windows, Linux, or macOS without recompilation, which is the foundation of Java's platform independence.

Answer

The JVM provides a set of precompiled native libraries that replace the need for bytecode, so programs run as native executables.

Answer

The JVM converts Java bytecode into C source code, which is then compiled by a native compiler for the target platform.

Answer

The JVM translates Java source code directly into native machine code for the host operating system before execution.

Question 5

A developer writes a method that is intended to double each element in an int array. The method is:

public static void doubleAll(int[] nums) {
    for (int i = 0; i < nums.length; i++) {
        nums[i] *= 2;
    }
}

What is the effect when the following code is executed?

int[] values = {1, 2, 3};
doubleAll(values);
System.out.println(values[1]);

Accepted Answer

The program prints 4, because the method modifies the shared array object.. When an array is passed to a method, the method receives a copy of the reference, so it can modify the elements of the caller's array. The indexed loop multiplies each element by 2, changing values[1] from 2 to 4. The method does not need to return the array because the modification is made directly to the shared object.

Answer

The program prints 2, because the enhanced for loop would be required to modify array elements.

Answer

The program prints 3, because the method does not return the modified array.

Answer

The program prints 2, because the method receives a copy of the array and changes do not affect the caller.

Question 6

A class contains these two methods:

public static void log(String message, int... codes) { }
public static void log(String message, int code) { }

A developer calls log("AUDIT", 42). Which statement describes what happens?

Accepted Answer

The fixed-arity method log(String, int) is selected, and no array is created.. Java resolves overloads in stages, testing fixed-arity applicability before permitting variable-arity matching. A single int argument fits the two-parameter method exactly, so that method wins and the varargs overload is never considered, meaning no implicit array packing happens at this call site.

Answer

The varargs method is selected because it is more flexible with the number of arguments.

Answer

The call is ambiguous and produces a compile-time error requiring a cast.

Answer

The call fails to compile because the two methods have the same erasure.

Question 7

A developer is converting a numeric string entered by a user into an int for arithmetic. The code reads: String input = "42"; int result = Integer.parseInt(input) + 8; System.out.println(result); The developer expects 50 to be printed. Which statement correctly describes what happens when this code executes?

Accepted Answer

The code prints 50 because Integer.parseInt converts the string "42" into the int 42.. Integer.parseInt parses the digit string "42" and yields the primitive int 42, so the plus operator performs numeric addition and prints 50. The method raises NumberFormatException only for malformed input, and a plain unsigned digit string is perfectly valid. No autoboxing or string concatenation is involved because the parser returns a primitive int.

Answer

The code throws NumberFormatException because "42" contains digits only and no sign character.

Answer

The code fails to compile because parseInt returns an Integer object, not an int.

Answer

The code prints 428 because the string and integer are concatenated by the plus operator.

Question 8

A developer is defining a Java interface named Payable that declares a method processPayment. The developer wants to ensure that any implementing class provides a concrete implementation of processPayment while the interface itself remains abstract. Which TWO statements about this interface design are true? (Choose two.)

Accepted Answer

A class that implements Payable must provide a body for processPayment or be declared abstract.. Interface methods without bodies are implicitly public and abstract, so a concrete implementer must override processPayment or be declared abstract. Java also permits a class to extend one superclass while implementing multiple interfaces, so combining Payable with a superclass is legal. Interfaces cannot be instantiated directly, cannot hold instance fields, and cannot use protected on their abstract methods.

Answer

Payable can declare instance fields that store per-object payment state.

Answer

Payable can be instantiated directly using the new keyword as long as processPayment is overridden.

Answer

The processPayment method in Payable must be declared with the protected access modifier.

Question 9

A developer is reviewing Java code and encounters several statements involving operators. Which TWO statements about Java operators are correct? (Choose two.)

Accepted Answer

The expression 5 % 2 evaluates to 1.. Integer division truncates toward zero, so 5 / 2 yields 2. The modulo operator returns the remainder, so 5 % 2 yields 1. These two statements accurately describe Java's behavior for integer arithmetic. The other options are incorrect: floating-point division by zero yields infinity, integer division by zero throws an exception, and multiplication has higher precedence than addition, so 5 + 2 * 3 equals 11.

Answer

The expression 5 / 0 evaluates to 0.

Answer

The expression 5 + 2 * 3 evaluates to 21.

Answer

The expression 5.0 / 0 evaluates to 0.

Question 10

A developer is explaining the role of the Java Virtual Machine to a colleague who is new to the platform. Which two statements accurately describe the JVM? (Choose two.)

Accepted Answer

It is specified independently of the underlying hardware and operating system, allowing bytecode to be portable across platforms.. The JVM is an abstract machine specified independently of any particular hardware or operating system, and its implementations execute bytecode while providing runtime services like memory management and thread scheduling. That combination is what makes compiled Java classes portable, since bytecode targets the abstract machine rather than a specific processor. Source compilation and native packaging are handled by other tools.

Answer

It is a single executable that is identical on every operating system and requires no platform-specific implementation.

Answer

It translates Java source code directly into machine code for the host operating system before execution begins.

Answer

It compiles and links multiple source files into a single native executable for distribution.

Question 11

A developer is debugging a Java application and wants to pause execution at a specific line in a method without modifying the source code. Which Java Development Kit tool allows setting a breakpoint at a class and line number before launching the program?

Accepted Answer

jdb. jdb is the JDK's command-line debugger. It attaches to or launches a Java program and supports commands that set breakpoints by class and line number, inspect variables, and step through execution. This allows a developer to pause at a specific line without editing the source, which is exactly what the scenario requires.

Answer

javap

Answer

jcmd

Answer

jconsole

Question 12

A development team is refactoring a Java application and must decide where to use abstract classes versus interfaces. Which two statements correctly describe legal and meaningful usage of an abstract class in Java? (Choose two.)

Accepted Answer

An abstract class may declare both abstract methods, which have no body, and concrete methods with full implementations.. Abstract classes uniquely combine unimplemented abstract methods with concrete methods and allow instance fields that hold state, making them ideal for partially implemented base types. They still obey single inheritance and still declare constructors that subclasses invoke, and they can never be instantiated directly with new.

Answer

A class may extend multiple abstract classes to combine their implementations.

Answer

An abstract class can be instantiated directly as long as all of its methods are concrete.

Answer

An abstract class cannot define a constructor because it can never be instantiated.

Question 13

A developer is writing a Java application that must terminate immediately when a critical configuration error occurs, without printing a stack trace or allowing any finally blocks to execute. Which statement should the developer use?

Accepted Answer

System.exit(1);. System.exit(int) halts the JVM at the point of invocation. Because the JVM shuts down before returning from the call, finally blocks associated with any active try statements do not execute, and no uncaught-exception stack trace is produced. This makes it the appropriate choice when a program must stop immediately on a fatal configuration error.

Answer

throw new RuntimeException("Configuration error");

Answer

assert false : "Configuration error";

Answer

return;

Question 14

A developer writes the following method to print all even numbers from 0 up to and including a supplied limit:

```java
void printEvens(int limit) {
    int n = 0;
    do {
        System.out.print(n + " ");
        n += 2;
    } while (n <= limit);
}
```

When the method is called as `printEvens(0)`, what is printed, and why?

Accepted Answer

0 is printed once, because the body executes before the condition is tested.. A do-while loop is a post-test loop: the body runs before the condition is examined, so the first value is always produced at least once. With n initialized to 0 and a limit of 0, the body prints 0, n becomes 2, and the check 2 <= 0 fails, ending the loop after one iteration. The result is a single printed value rather than none.

Answer

The method fails to compile, because a do-while loop cannot be used without an explicit initialization.

Answer

Nothing is printed, because the loop condition is evaluated before the first iteration.

Answer

0 and 2 are printed, because the condition is checked after each increment but the loop runs twice.

Question 15

A developer is writing a Java program that must print the numbers 1 through 10, but only even numbers should be printed. The developer writes:

for (int i = 1; i <= 10; i++) {
    if (i % 2 != 0) {
        continue;
    }
    System.out.print(i + " ");
}

What is the output?

Accepted Answer

2 4 6 8 10. The continue statement inside the if block causes the loop to skip the print statement whenever i is odd, because i % 2 != 0 evaluates to true for odd numbers. Even values fall through to the print statement. Since the loop runs from 1 through 10, the values that survive the skip are 2, 4, 6, 8, and 10, printed in ascending order with a trailing space.

Answer

10 8 6 4 2

Answer

1 3 5 7 9

Answer

1 2 3 4 5 6 7 8 9 10