1Z0-811 Java Basics and Syntax — 15 Questions

Question 1

Which code snippets correctly create a two-dimensional array with 3 rows and 4 columns? (Select all that apply)

Accepted Answer

int[] array[] = new int[3][4];. Options B and D are both correct. In Java, a two-dimensional array can be declared using either `int[][] array = new int[3][4];` (Option D) or `int[] array[] = new int[3][4];` (Option B). Both syntaxes are valid and create a 3x4 array. Options A and C are incorrect because Java does not use commas to separate dimensions; each dimension must be in its own set of brackets.

Answer

int[][] array = new int[3,4];

Answer

int array[][] = new int[3,4];

Question 2

Which FOUR statements about the main method are correct? (Choose four.)

Accepted Answer

It must be declared void.. Options A, B, and C are correct because the main method must be declared void, static, and public for the JVM to invoke it as the entry point of a program. Option E is also correct: Java allows overloading of the main method; you can define multiple main methods with different parameter lists, but only the one with the standard signature `public static void main(String[] args)` is used as the program entry point. Option D is incorrect because the main method must not return a value; its return type must be void.

Answer

It must return an int.

Question 3

A developer needs to declare a constant for the value of PI (3.14159) in a class. Which declaration follows Java best practices?

Accepted Answer

public static final double pi = 3.14159;. The best choice because Java best practices for constants require the use of the `public static final` modifiers to create a class-level constant. While the naming convention recommends uppercase names (e.g., `PI`), the presence of `public static final` is more critical for a constant to be accessible and immutable across the class. Option A lacks `public` and `static`, making it an instance constant rather than a class constant, which does not follow best practices. Therefore, among the given choices, Option C is the most appropriate.

Answer

final double PI = 3.14159;

Answer

double pi = 3.14159;

Answer

final double pi = 3.14159;

Question 4

Which THREE are valid Java identifiers? (Choose three.)

Accepted Answer

$dollar. Options A, D, and E are valid Java identifiers. Java identifiers must start with a letter (a-z, A-Z), underscore (_), or dollar sign ($). Subsequent characters can include letters, digits, underscores, or dollar signs. Option A ($dollar) starts with $, valid. Option D (_value) starts with _, valid. Option E (myVar123) starts with a letter and contains digits, valid. Option B (my var) contains a space, invalid. Option C (2ndValue) starts with a digit, invalid.

Answer

my var

Answer

2ndValue

Question 5

A class has two methods: void setValue(int a) and void setValue(double a). Which call will result in a compilation error?

Accepted Answer

setValue(5); setValue(5.0); both in same class. Since the class contains both overloaded methods void setValue(int a) and void setValue(double a), all the provided calls are valid and compile without error. setValue(5) calls the int version, setValue(5.0) calls the double version, and setValue((int)5.0) explicitly casts to int, calling the int version. Option B consists of two separate valid calls within the same class, so no compilation error occurs. Therefore, none of the options result in a compilation error.

Answer

setValue(5.0);

Answer

setValue(5);

Answer

setValue((int)5.0);

Question 6

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 7

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.

Question 8

A developer writes the following code: int x = 5; System.out.println(x++); What is the output?

Accepted Answer

5. The expression `x++` is a post-increment operator, which returns the current value of `x` (5) before incrementing it. Therefore, `System.out.println(x++)` prints 5, and then `x` becomes 6. Option B is correct because the output is the original value of `x`.

Answer

Compilation error

Answer

6

Answer

Runtime exception

Question 9

A team decides to use a single Java source file for a small application. Which statement is true about the file structure?

Accepted Answer

It can contain exactly one public class with the same name as the file.. In Java, when a source file contains a public class, the file name must exactly match the public class name, including case sensitivity. This is a fundamental rule enforced by the Java compiler to ensure proper class loading and package structure. The file can have at most one public top-level class, and that class name determines the file name.

Answer

It must have a main method to compile.

Answer

It can contain multiple public classes.

Answer

The public class name can differ from the file name.

Question 10

Given the code: String s1 = "Java"; String s2 = new String("Java"); if (s1 == s2) { System.out.print("Equal"); } else { System.out.print("Not Equal"); } What is the output?

Accepted Answer

Not Equal. The == operator compares object references, not the actual string content. s1 is a string literal stored in the string pool, while s2 is a new String object created on the heap, so they refer to different memory locations, making the comparison false and printing 'Not Equal'.

Answer

Runtime error

Answer

Compilation error

Answer

Equal

Question 11

Which primitive data type should be used to store a single character?

Accepted Answer

char. The `char` primitive data type in Java is specifically designed to store a single 16-bit Unicode character, ranging from '\u0000' (0) to '\uffff' (65,535). It can represent any character in the Unicode standard, including letters, digits, and symbols, making it the appropriate choice for a single character value.

Answer

int

Answer

byte

Answer

String

Question 12

A method is declared as: public static void main(String[] args) { }. Which statement is true?

Accepted Answer

The method can be called without creating an instance of the class.. The `static` modifier in the method signature means the method belongs to the class itself, not to any instance. Therefore, it can be invoked using the class name (e.g., `ClassName.main(args)`) without creating an object of the class. This is a fundamental characteristic of static methods in Java.

Answer

The method can be overridden in a subclass.

Answer

The method can return an int.

Answer

The method can be private.

Question 13

What is the value of the expression (10 > 5) && (3 < 2)?

Accepted Answer

false. The expression (10 > 5) evaluates to true, and (3 < 2) evaluates to false. The logical AND operator (&&) returns true only if both operands are true. Since one operand is false, the entire expression evaluates to false. In Java, the result of a boolean expression is a boolean literal, not an integer.

Answer

1

Answer

true

Answer

0

Question 14

Which loop construct guarantees that the body executes at least once?

Accepted Answer

do-while loop. The do-while loop is a post-test loop, meaning the condition is evaluated after the loop body executes. This guarantees that the body runs at least once, regardless of whether the condition is initially true or false. In contrast, for, while, and enhanced for loops are pre-test loops that check the condition before entering the body, so they may execute zero times.

Answer

enhanced for loop

Answer

for loop

Answer

while loop

Question 15

Given the code: int[] arr = {1,2,3}; for(int x : arr) { if(x==2) continue; System.out.print(x); } What is the output?

Accepted Answer

13. The enhanced for loop iterates over the array {1,2,3}. When x equals 2, the continue statement skips the remainder of the loop body for that iteration, so System.out.print(x) is not executed for 2. Thus, only 1 and 3 are printed, producing output '13'.

Answer

2

Answer

Compilation error

Answer

123