1Z0-811 Practice Test 20 — 15 Questions

Question 1

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. To identify the source of a NullPointerException, the most effective actions are examining the stack trace (option C) and using a debugger (option B). The stack trace shows the exact line number and method call sequence where the exception occurred, pinpointing the location. A debugger allows you to step through code, inspect variable states, and observe the flow leading to the null reference. While System.out.println (A), catching the exception and printing its message (E), and recompiling with -g (D) can provide debugging information, they are not as direct or efficient for locating the root cause; notably, catching the exception does not prevent it and only prints the message without full stack details.

Answer

Use System.out.println statements

Answer

Recompile with -g flag

Answer

Catch the exception and print its message

Question 2

Which TWO of the following are valid loop constructs in Java? (Choose two.)

Accepted Answer

do {} while (false);. A valid do-while loop; the semicolon after the condition is required. Option E is a standard for loop. Option B is invalid because 'while (true)' lacks a loop body (statement or block). Option C uses incorrect syntax: 'for each' is not Java; the correct syntax is 'for (int i : array)'. Option D uses 'loop' which is not a Java keyword; the correct keyword is 'for'.

Answer

while (true)

Answer

for each (int i : array) {}

Answer

loop (int i = 0; i < 10; i++) {}

Question 3

What is the value of z after executing: int x = 3; int y = 2; int z = x++ * --y;

Accepted Answer

3. The expression `x++ * --y` uses post-increment on `x` and pre-decrement on `y`. Post-increment returns the original value of `x` (3) before incrementing it to 4. Pre-decrement decrements `y` from 2 to 1, then returns the new value (1). The multiplication is 3 * 1 = 3, which is assigned to `z`. So the correct answer is 3.

Answer

6

Answer

4

Answer

2

Question 4

Which two statements are true about primitive data types in Java?

Accepted Answer

The long data type can store values from -2^63 to 2^63-1.. Options A and B are correct. The long data type is 64-bit with a range from -2^63 to 2^63-1. The short data type is 16-bit with a range from -32,768 to 32,767. Option C is false because the float data type is 32-bit and cannot represent decimal numbers precisely; it is an approximate type. Option D is false because the boolean data type's size is not strictly defined; it is typically represented as a byte or word, not a single bit. Option E is false because the char data type stores Unicode characters (16-bit) and can represent a wide range of characters beyond ASCII.

Answer

The float data type is 32-bit and can represent decimal numbers precisely.

Answer

The boolean data type has a size of 1 bit.

Answer

The char data type can store only ASCII characters.

Question 5

A developer is using the Oracle Java Platform Debugger Architecture (JPDA) to debug a remote Java application. Which command-line option is required to start the application in debug mode listening on port 5005?

Accepted Answer

-agentlib:jdwp=transport=dt_socket,server=y,suspend=n,address=5005. The `-agentlib:jdwp` option is the modern, recommended way to enable the Java Debug Wire Protocol (JDWP) for remote debugging. It specifies the transport as `dt_socket` (TCP/IP sockets), sets the JVM as the debug server (`server=y`), does not suspend the application on startup (`suspend=n`), and listens on port 5005 (`address=5005`). This is the standard JPDA configuration for attaching a debugger to a running Java application.

Answer

-javaagent:debug.jar=port=5005

Answer

-Xdebug -Xrunjdwp:transport=dt_socket,server=y,address=5005

Answer

-Ddebug=true -Dport=5005

Question 6

Refer to the exhibit. What is the output?

Accepted Answer

10. The code initializes x to 10. The if condition is false (10 is not greater than 15), so the increment is skipped. Therefore, x remains 10, and the output is 10.

Answer

11

Answer

0

Answer

9

Question 7

What is the output of the following code?

int x = 5;
int y = 16;
System.out.print(x + "," + y);

Accepted Answer

5,16. The code initializes `int x = 5;` and `int y = 16;` and then prints them using `System.out.print(x + "," + y);`. Since there are no operations that change the values, the output is simply the initial values: 5,16. Therefore, option A is correct.

Answer

4,16

Answer

4,12

Answer

5,12

Question 8

A developer is writing a program to find the maximum value in an array of integers. The code is:

int[] nums = {10, 20, 5, 30, 15};
int max = 0;
for (int i = 0; i < nums.length; i++) {
    if (nums[i] > max) {
        max = nums[i];
    }
}
System.out.println(max);

The output is 30, which is correct for this array. However, the developer is concerned that if all numbers are negative, the output would be 0 instead of the highest negative number. Which modification ensures the algorithm works correctly for all integer arrays?

Accepted Answer

Initialize max to Integer.MIN_VALUE.. The issue is that initializing max to 0 fails when all numbers are negative, because max would remain 0 (greater than any negative number). Both options A and C correctly fix this: Option A initializes max to Integer.MIN_VALUE, ensuring that any array element will be greater than or equal to max. Option C initializes max to nums[0] and starts the loop from index 1, guaranteeing max is set to an actual array element. Option B is flawed because checking if max equals 0 after changes is not reliable. Option D with a boolean flag is unnecessarily complex and still requires proper initialization. Therefore, both A and C are correct modifications.

Answer

Before assigning, check if max equals 0; if so, assign regardless.

Answer

Add a boolean flag to track if any element has been processed.

Question 9

Which THREE are valid loop constructs in Java? (Choose three.)

Accepted Answer

while (condition) { }. The `while` loop is a standard Java construct that repeatedly executes a block of code as long as the specified boolean condition evaluates to `true`. The syntax `while (condition) { }` is valid even with an empty body, as the condition is checked before each iteration.

Answer

repeat { } until (condition);

Answer

loop (condition) { }

Question 10

Refer to the exhibit. The code at line 6 of ArrayExample.java is: int[] arr = {10, 20, 30, 40, 50}; int sum = 0; for (int i = 0; i <= arr.length; i++) sum += arr[i]; Which change fixes the exception?

Accepted Answer

Change loop condition to i < arr.length. The exception occurs because the loop condition `i <= arr.length` causes the loop to iterate one index beyond the array's last valid index (arr.length - 1). When `i` equals `arr.length` (5), `arr[5]` is accessed, which throws an ArrayIndexOutOfBoundsException. Changing the condition to `i < arr.length` ensures the loop runs only for indices 0 through 4, fixing the exception. Option D, changing `arr.length` to `arr.length - 1` in the condition, also technically fixes the exception, but it is not the standard or recommended fix; the intended correct answer is to use the `<` operator.

Answer

Change array declaration to int[] arr = new int[6];

Answer

Change loop initialization to i = 1

Question 11

A subclass overrides a method from its superclass. Which annotation should be used to indicate the overriding intention?

Accepted Answer

The @Override annotation is optional but recommended. The @Override annotation is optional in Java; the compiler will still enforce method overriding without it. However, it is strongly recommended because it provides a compile-time check that the method correctly overrides a superclass method, preventing accidental overloading or typos in the method signature.

Answer

The @Override annotation is not allowed

Answer

The @Override annotation is used for overloading

Answer

The @Override annotation is mandatory

Question 12

A developer uses the following array initialization:
int[] nums = new int[]{1, 2, 3};
Which of the following is true?

Accepted Answer

The array has length 3.. The array initialization `int[] nums = new int[]{1, 2, 3};` explicitly creates an array of length 3, containing the elements 1, 2, and 3. The syntax is valid and the array is not initialized with default values; it is initialized with the specified literal values.

Answer

This is invalid syntax.

Answer

The array is initialized with default values.

Answer

The array can only store numbers up to 3.

Question 13

A developer wants to ensure that a class cannot be subclassed. Which keyword should be used?

Accepted Answer

final. The `final` keyword prevents a class from being subclassed. When a class is declared `final`, the compiler enforces that no other class can extend it, ensuring its implementation cannot be overridden or inherited. This is the correct mechanism in Java to prevent subclassing.

Answer

protected

Answer

private

Answer

abstract

Answer

static

Question 14

Which THREE statements are true about the switch statement in Java? (Choose three.)

Accepted Answer

Without a break statement, execution falls through to the next case.. Options C, D, and E are true. Option C correctly describes fall-through behavior: without a break statement, execution continues to the next case. Option D correctly states that the default case is optional. Option E is true because, since Java 7, the switch statement can be used with String objects. Options A and B are false: A is incorrect because switch does not support boolean expressions; B is incorrect because the default case can appear anywhere in the switch block.

Answer

It can be used with boolean expressions.

Answer

The default case must be placed at the end of the switch block.

Question 15

Which TWO command-line tools are included in the Oracle JDK for monitoring and troubleshooting Java applications? (Select exactly 2)

Accepted Answer

jstack. jstack is a command-line tool included in the Oracle JDK that prints Java stack traces of threads for a given Java process or core dump. It is used to diagnose deadlocks, thread contention, and other concurrency issues by showing the state and call stack of each thread.

Answer

jmod

Answer

javap

Answer

jdb