1Z0-811 Java Basics and Syntax — All Questions With Answers

A developer writes the following code to compare two strings: String s1 = "Java"; String s2 = new String("Java");

if (s1 == s2) { System.out.println("Equal"); } else { System.out.println("Not equal"); }

What is the output?

A method is declared as:

public void setAge(int age) { this.age = age; }

Which statement is correct about this code assuming the class has an instance variable age?

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?

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?

A mobile app backend uses Java streams to process user data. The code snippet filters users who are active and older than 18, then collects them into a list:

List<User> result = users.stream() .filter(u -> u.isActive()) .filter(u -> u.getAge() > 18) .collect(Collectors.toList());

Performance metrics show that this stream operation is slow when the user list has millions of entries. The team wants to improve performance without changing the business logic. Which change would most likely improve performance?

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?

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?