1Z0-811 Java Basics and Syntax Practice Test 2 — 15 Questions

Question 1

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 2

Refer to the exhibit. What is the most likely cause?

Accepted Answer

The code tries to access index 5 of a 5-element array.. Java arrays are zero-indexed, meaning a 5-element array has valid indices 0 through 4. Accessing index 5 attempts to read beyond the array bounds, causing an ArrayIndexOutOfBoundsException at runtime. This is a classic off-by-one error where the code mistakenly uses the array length as the index.

Answer

The array has 6 elements.

Answer

The code tries to access index 4 of a 5-element array.

Answer

The code has a syntax error.

Question 3

A company requires a method that accepts an integer and returns true if the integer is even, otherwise false. Which implementation best follows Java conventions?

Accepted Answer

public boolean isEven(int num) { return num % 2 == 0; }. It defines a method with the appropriate return type `boolean`, uses a clear and conventional name `isEven`, and returns the result of the expression `num % 2 == 0` directly. This follows Java naming conventions (camelCase with a verb for boolean methods) and leverages the fact that `%` yields the remainder, which is compared to zero to produce a boolean result.

Answer

public void isEven(int num) { System.out.println(num%2==0); }

Answer

public int isEven(int num) { return num % 2; }

Answer

public boolean evenCheck(int num) { if(num%2==0) return true; else return false; }

Question 4

Given the loop: for (int i=0; i<5; i++) { if (i==2) continue; System.out.print(i); } What is the output?

Accepted Answer

0134. The loop iterates i from 0 to 4. When i equals 2, the 'continue' statement skips the rest of that iteration, so 'System.out.print(i)' is not executed for i=2. Therefore, the output is 0, 1, 3, 4 concatenated as '0134'. Options A and C both display '0134' and are therefore correct. Option B shows '0124' (missing 3) and Option D shows '01234' (includes 2), both incorrect.

Answer

0124

Answer

01234

Question 5

What is the result of the following code? String s1 = "Hello"; String s2 = " World"; String s3 = s1 + s2; System.out.println(s3);

Accepted Answer

Hello World. The + operator performs string concatenation in Java. s1 + s2 combines "Hello" and " World" to produce "Hello World", which is then printed. The space is part of s2, so the output includes it.

Answer

HelloWorld

Answer

Hello World

Answer

Compilation error

Question 6

Which statement about try-catch is true?

Accepted Answer

A catch block can only handle one type of exception.. In Java, a catch block is defined with a single exception type parameter, meaning it can only handle one specific type of exception (or its subclasses if the parameter is a superclass). This is enforced by the language syntax: `catch (ExceptionType e)` allows only one exception type per catch clause.

Answer

A finally block is always required.

Answer

A try block without a catch or finally is legal.

Answer

A try block can have multiple catch blocks for the same exception type.

Question 7

Which THREE are primitive data types in Java? (Choose three.)

Accepted Answer

double. Options A, C, and D are correct because double, boolean, and int are all Java primitive data types defined by the Java language specification, each holding a raw value rather than a reference to an object. double is an 8-byte IEEE 754 floating-point primitive, boolean is the primitive type representing true/false, and int is a 4-byte signed two's-complement integer primitive. Options B and E are not primitive: Integer is a wrapper class in java.lang that boxes the int primitive, and String is a reference type (a class) representing immutable character sequences, so neither is a primitive data type.

Answer

Integer

Answer

String

Question 8

The code does not compile. What is the error?

Accepted Answer

Assignment instead of comparison in if condition. The code uses a single equals sign `=` (assignment) inside the `if` condition instead of `==` (comparison). In Java, `if (x = 5)` assigns the value 5 to `x` and then evaluates the assignment expression to the assigned value (5), which is an `int`, not a `boolean`. The `if` statement requires a `boolean` expression, so this causes a compilation error.

Answer

Missing semicolon after if condition

Answer

Variable x is not initialized

Answer

System.out.println syntax error

Question 9

Which THREE are valid ways to declare and initialize a two-dimensional int array in Java?

Accepted Answer

int[][] arr = new int[2][2];. Option A is correct because `int[][] arr = new int[2][2];` legally allocates a rectangular 2D array with 2 rows and 2 columns, and Java automatically initializes all int elements to 0. Option B is correct because `int[][] arr = new int[2][4];` is a valid rectangular allocation of 2 rows by 4 columns, again with default zero values. Option E is correct because `int[][] arr = {{1,2},{3,4}};` uses an array initializer to declare and initialize a 2D int array directly, which is valid Java syntax. Option C is invalid because Java does not allow omitting the first dimension size while specifying the second dimension in `new int[][2]`. Option D is invalid because you cannot combine an explicit dimension size like `new int[2][2]` with an array initializer block `{{1,2},{3,4}}`; the correct initializer form omits the `new int[...]` dimensions.

Answer

int[][] arr = new int[][2];

Answer

int[][] arr = new int[2][2]{{1,2},{3,4}};

Answer

int[][] arr = new int[2][];

Question 10

A financial trading application processes high-volume transactions. The system uses a multithreaded architecture where multiple threads update a shared Account object's balance field. Recently, intermittently incorrect balance calculations have been reported. Developers suspect a race condition on the balance field. The Account class is defined as follows:

public class Account {
    private double balance = 0.0;
    public void deposit(double amount) { balance += amount; }
    public void withdraw(double amount) { balance -= amount; }
    public double getBalance() { return balance; }
}

Threads are created using ExecutorService with a fixed thread pool. The issue occurs only under heavy load. Which course of action should the development team take to resolve the issue while maintaining performance?

Accepted Answer

Synchronize the deposit and withdraw methods.. Synchronizing the `deposit` and `withdraw` methods ensures mutual exclusion on the `balance` field. In Java, the compound operations `balance += amount` and `balance -= amount` are not atomic; they involve a read, modify, and write sequence. Synchronization guarantees that only one thread executes these methods at a time, preventing race conditions and ensuring correct balance calculations under heavy load.

Answer

Declare the balance field as volatile.

Answer

Use AtomicLong and convert to double.

Answer

Wrap the balance field in a synchronized block within each method using a separate lock object.

Question 11

A web application uses a HashMap to cache user session data. The keys are String objects representing session IDs, and values are Session objects. After some time, the cache memory usage grows excessively, causing OutOfMemoryError. The cache is never cleared. The team decides to implement a cache eviction policy. Which approach is best suited for this scenario in terms of Java standard library?

Accepted Answer

Use LinkedHashMap with removeEldestEntry method.. LinkedHashMap provides a straightforward way to implement a cache eviction policy by overriding the `removeEldestEntry` method. This method is automatically called by `put` and `putAll` to decide whether to remove the eldest entry, allowing you to limit the cache size and prevent OutOfMemoryError without manual eviction logic.

Answer

Use WeakHashMap instead of HashMap.

Answer

Wrap the HashMap with Collections.synchronizedMap.

Answer

Use TreeMap with a custom comparator.

Question 12

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 13

You are tasked with debugging a Java application that processes temperature sensor readings. The application reads an array of double values representing temperatures in Celsius, and should output the number of readings that exceed a threshold of 30.0°C. The current implementation is:

public class TemperatureAnalyzer {
    public static void main(String[] args) {
        double[] readings = {25.5, 32.1, 30.0, 28.9, 35.7};
        int count = 0;
        for (int i = 0; i < readings.length; i++) {
            if (readings[i] > 30.0) {
                count++;
            }
        }
        System.out.println("Count: " + count);
    }
}

However, the output is "Count: 3" instead of the expected 2 (since 30.0 is not above the threshold). The developer believes the issue is that the condition should be '>=' to include 30.0, but the specification says strictly above 30.0. After further investigation, you discover that the problem is due to floating-point imprecision when comparing with the literal 30.0. Which of the following changes would correctly fix the comparison to reliably count readings strictly greater than 30.0, considering floating-point representation?

Accepted Answer

Change the data type of readings to int and multiply all values by 10 to preserve one decimal place, then compare with 300.. It avoids floating-point imprecision entirely by using integer arithmetic. Multiplying the readings by 10 and converting to int preserves one decimal place exactly, allowing a direct comparison with 300 (which corresponds to 30.0). This ensures that only readings strictly greater than 30.0 are counted, without risk of tiny rounding errors affecting the result.

Answer

Change the condition to (readings[i] - 30.0) > Double.MIN_VALUE.

Answer

Change the condition to Math.abs(readings[i] - 30.0) > 0.0.

Answer

Change the threshold literal to 30.0f (float) and compare using Float.compare(readings[i], threshold) > 0.

Question 14

What is the result of compiling and running this code?

Accepted Answer

Compilation error. The code fails to compile because it attempts to assign a double value (10.5) to an int variable without an explicit cast. In Java, narrowing primitive conversions (double to int) are not allowed implicitly; the compiler requires a cast like (int) 10.5 to acknowledge potential loss of precision. Therefore, the compilation error occurs before any output is produced.

Answer

15

Answer

10.5

Answer

15.5

Answer

16

Question 15

A developer is building a Java application for a bank that processes account transactions. The application reads transaction amounts from a CSV file provided by a third party. The amounts are in string format, e.g., '1,234.56' or '$5,000.00'. The developer uses Integer.parseInt() to convert these strings to integers for processing. However, many transactions fail with NumberFormatException. The developer adds a try-catch block to catch the exception and log the error. But still, the application fails to process valid transactions because the parsing does not handle the formatting. The development team is considering several approaches to fix this issue. The goal is to parse the string into an integer representing the whole dollar amount (ignoring cents and formatting). Which course of action should the developer take?

Accepted Answer

Use String.replaceAll("[^0-9]", "") to remove non-digit characters before parsing.. The best approach among the options is to first remove commas, dollar signs, and other non-digit characters except the decimal point, then parse the cleaned string using BigDecimal, and finally convert to int using intValue(), which truncates the decimal part. This correctly ignores cents. Option D removes non-digit characters including the decimal point, causing cents digits to be included, resulting in an incorrect integer (e.g., '500000' instead of 5000). Option C suffers from a similar issue as it extracts all digit sequences including cents. Option B does not address the formatting problem. Therefore, option A, though requiring prior cleaning, is the most appropriate course of action.

Answer

Use BigDecimal to represent the value and then convert to int using intValue().

Answer

Use a custom parser that throws a checked exception to enforce proper formatting.

Answer

Use a Scanner with useDelimiter("[^0-9]") to extract digits.