1Z0-811 Java Basics and Syntax Practice Test 5 — 15 Questions

Question 1

A class has a static variable counter initialized to 0. Two threads increment counter 1000 times each using counter++. What is a possible final value of counter?

Accepted Answer

Any value between 1000 and 2000 inclusive. `counter++` is not an atomic operation; it consists of three steps: read, increment, and write. When two threads execute this non-atomic operation concurrently without synchronization, interleaving can cause lost updates, resulting in a final value that is less than 2000 but at least 1000 (since each thread increments at least once). The possible final value is any integer between 1000 and 2000 inclusive.

Answer

1000

Answer

0

Answer

2000

Question 2

Which is the correct way to declare an array of integers in Java?

Accepted Answer

Both A and B are valid.. In Java, arrays can be declared with the brackets either after the type (e.g., int[] array = new int[5];) or after the variable name (e.g., int array[] = new int[5];). Both syntaxes are valid, so the correct answer is the option that states both are valid. Option C (int array = new int[5];) is invalid because it declares an integer variable, not an array, and omits the brackets.

Answer

int[] array = new int[5];

Answer

int array = new int[5];

Answer

int array[] = new int[5];

Question 3

A developer writes: if (x = 5) { System.out.println("x is 5"); } What is the result?

Accepted Answer

Compilation error. In Java, the assignment operator `=` is used for assignment, not comparison. The expression `x = 5` assigns the value 5 to variable `x` and returns the assigned value (5). Since the condition in an `if` statement must be a boolean expression, and `int` cannot be implicitly converted to `boolean`, the compiler throws a compilation error. This is a fundamental syntax rule in Java, unlike in C/C++ where such an assignment would be allowed as a truthy check.

Answer

Prints "x is 5" if x equals 5

Answer

No output

Answer

Prints "x is 5" always

Question 4

Which TWO statements are true about the main method?

Accepted Answer

It must be declared public.. The Java Language Specification (JLS) requires the main method to be declared public so that the JVM can access it from outside the class. Option D is correct because the main method must be static, allowing the JVM to invoke it without creating an instance of the class.

Answer

It must be declared final.

Answer

It must return an int.

Answer

It cannot be overloaded.

Question 5

Which THREE of the following are primitive data types in Java?

Accepted Answer

double. `double` is one of the eight primitive data types in Java, used to store floating-point numbers with double precision (64-bit IEEE 754). It is a fundamental type that holds a numeric value directly, not an object reference.

Answer

String

Answer

array

Question 6

Which TWO are valid ways to create a String object?

Accepted Answer

String s = "hello";. Using a string literal ("hello") creates a String object automatically via the JVM's string constant pool, which is a standard and valid way. Option E is correct because the String constructor new String(String) takes another String as an argument, here "hello", which is valid. Option A is incorrect because null is not an object; it is a reference that does not point to any object. Option B is incorrect because the String constructor expects a String or other char sequence, not an int literal. Option D is incorrect because single quotes denote a char literal, not a String.

Answer

String s = null;

Answer

String s = new String(10);

Answer

String s = 'hello';

Question 7

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 8

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 9

Given the following code:

class A {
    A() { System.out.print("A "); }
}
class B extends A {
    B() { System.out.print("B "); }
}
class C extends B {
    C() { System.out.print("C"); }
    public static void main(String[] args) {
        new C();
    }
}

What is the output when running the main method?

Accepted Answer

A B C. In Java, when an object of a subclass is created, constructors are executed from the topmost superclass down to the subclass. Assuming the exhibit shows class C extends B extends A, with each constructor printing its class name, the output will be A B C.

Answer

B A C

Answer

A C B

Answer

C B A

Question 10

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?

Accepted Answer

Not equal. The == operator compares object references, not the actual string content. Variable s1 refers to a string literal from the string pool, while s2 is a new String object created on the heap, so they are different objects and the comparison returns false, printing 'Not equal'.

Answer

Compilation error

Answer

Equal

Answer

Runtime error

Question 11

A package named com.example.util is declared in a file. Where should the file be placed in the directory structure?

Accepted Answer

com/example/util/. Java requires that the directory structure of a package matches the package declaration. A package named `com.example.util` must be stored in a directory hierarchy `com/example/util/` so that the Java compiler and runtime can locate the class files based on the fully qualified name. This ensures that the file is accessible via the classpath or module path.

Answer

com.example.util/

Answer

util/

Answer

com/example/util.java

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 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?

Accepted Answer

The method sets the instance variable age.. The method `setAge(int age)` uses the `this` keyword to assign the parameter value to the instance variable `age`, which is a standard setter pattern in Java. The method has a `void` return type and is not a constructor, and it compiles successfully because the instance variable `age` is assumed to exist in the class.

Answer

The method is a constructor.

Answer

The method will cause a compilation error.

Answer

The method is static.

Question 14

A developer writes the following code: int x = 5; int y = x++; What are the values of x and y after execution?

Accepted Answer

x = 6, y = 5. The post-increment operator `x++` returns the original value of `x` (5) before incrementing. Therefore, `y` is assigned 5, and `x` becomes 6 after the increment. This is a fundamental behavior of post-increment in Java.

Answer

x = 5, y = 5

Answer

x = 5, y = 6

Answer

x = 6, y = 6

Question 15

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; }