1Z0-811 Practice Test 5 — 25 Questions

Question 1

A developer implements a method to check if a number exists in an array using binary search. The array is not sorted. What will happen?

Accepted Answer

The method returns incorrect results sometimes.. Binary search requires the array to be sorted to work correctly. If the array is not sorted, the algorithm may skip over the target element or incorrectly conclude it is absent, leading to incorrect results. Therefore, the method returns incorrect results sometimes.

Answer

The method returns correct results always.

Answer

Runtime exception.

Answer

Compilation error.

Question 2

Which two of the following are primitive data types in Java? (Choose two)

Accepted Answer

boolean. `boolean` is a primitive data type in Java that can hold only two values: `true` or `false`. It is not an object and does not have methods, making it a fundamental building block for conditional logic.

Answer

Character

Answer

String

Answer

Integer

Question 3

A developer declares an integer variable inside a method but does not assign a value. What is the result of attempting to print the variable?

Accepted Answer

Compilation error. In Java, local variables (declared inside a method) must be initialized before use. The compiler performs definite assignment analysis and will reject code that attempts to read an uninitialized local variable, producing a compilation error. This rule ensures memory safety and prevents undefined behavior.

Answer

Prints null

Answer

Prints 0

Answer

Runtime exception

Question 4

What is the output of the code?

```java
for (int i = 0; i < 5; i++) {
    if (i == 2) {
        continue;
    }
    System.out.print(i + " ");
}
```

Accepted Answer

0 1 3 4. The code uses a for loop that iterates from i = 0 to i < 5 (i.e., 0 through 4). Inside the loop, there is an if condition that checks if i equals 2. When i == 2, the continue statement is executed, which skips the rest of that iteration, so the System.out.print statement is not executed for i = 2. Therefore, the loop prints 0, 1, 3, and 4, each followed by a space. Option D correctly lists this output.

Answer

0 1 2 3 4

Answer

1 3 4

Answer

0 1 2 3

Question 5

A developer writes code to calculate the average of two integers: int a = 5; int b = 10; int avg = a / b;. Which change ensures the average is correctly calculated as a double?

Accepted Answer

Cast one operand to double: (double) a / b. In Java, when both operands of the division operator are integers, integer division is performed, truncating the fractional part. By casting one operand to double, the operation becomes floating-point division, yielding a double result (0.5). This ensures the average is calculated correctly as a double.

Answer

No change needed; integer division is correct

Answer

Change the variable types to double

Answer

Use Math.round(a / b)

Question 6

Which is the correct way to call a superclass constructor from a subclass constructor?

Accepted Answer

super(); as first statement. In Java, a call to the superclass constructor using `super()` must be the first statement in a subclass constructor. This ensures that the superclass initialization completes before any subclass-specific code executes, maintaining the inheritance chain. Option B correctly identifies this requirement.

Answer

super(); anywhere

Answer

super(); at the end

Answer

this.super();

Question 7

Which THREE are benefits of Java's platform independence? (Choose three.)

Accepted Answer

Ability to run on any device with a JVM. Options A, B, and E are correct. Java's platform independence allows code to run on any device with a JVM (A), enables the 'write once, run anywhere' principle (B), and enhances security through sandboxing, which isolates untrusted code (E). Option C is incorrect because faster execution compared to native code is not a benefit; Java often runs slower due to interpretation or JIT compilation. Option D is incorrect because automatic memory management (garbage collection) is a feature of the JVM but not directly a benefit of platform independence; it is a separate advantage of Java.

Answer

Faster execution compared to native code

Answer

Automatic memory management

Question 8

A method is needed to return a new array where each element is doubled. Which method signature correctly accomplishes this?

Accepted Answer

public int[] doubleArray(int[] input). The method must return a new array with doubled values, so the return type must be `int[]` (an array of integers) and the parameter must be an `int[]` (the input array). This signature allows the method to accept an array, process each element, and return a new array of the same length with each element doubled.

Answer

public int doubleArray(int[] input)

Answer

public int[] doubleArray(int input)

Answer

public void doubleArray(int[] input)

Question 9

Which TWO of the following development tools are specifically designed to analyze module dependencies or create custom runtime images?

Accepted Answer

jdeps. The jdeps tool (option A) is a Java class dependency analyzer that examines class files or JARs to identify module-level dependencies, including transitive dependencies, and can suggest module dependencies for migration to the Java module system. The jlink tool (option B) is a Java linker that assembles and optimizes a set of modules and their dependencies into a custom runtime image, allowing you to create a minimal JRE tailored to your application.

Answer

jar

Answer

javadoc

Answer

javac

Question 10

A method receives an int parameter and modifies its value inside the method. Does this change affect the caller's argument?

Accepted Answer

No, because Java passes a copy of the value. Java uses pass-by-value for all parameters. When an int is passed to a method, a copy of the value is made, so modifications inside the method affect only the copy, not the original variable in the caller's scope.

Answer

No, unless the parameter is marked as volatile

Answer

Yes, because the parameter is an int

Answer

Yes, because Java passes a reference

Question 11

Refer to the exhibit. What is the problem with this class?

Accepted Answer

The constructor parameter shadows the field, causing name to remain null. The constructor parameter 'name' shadows the field 'name'. The assignment 'name = name' assigns the parameter to itself, leaving the field 'name' uninitialized (null). Option A is incorrect because constructors do not have a return type. Option C is incorrect because getName() returns a String, and it is fine to not be void. Option D is incorrect because the private field is accessible within the class.

Answer

The constructor is missing a return type

Answer

The getName method should be void

Answer

The field name is private and cannot be accessed within the class

Question 12

Which TWO of the following are valid Java identifiers?

Accepted Answer

_count. (_count) is a valid Java identifier because identifiers can begin with an underscore (_) or a dollar sign ($), and can contain letters, digits, underscores, and dollar signs. Java allows underscores as the first character, though this is discouraged in modern Java style guides.

Answer

class

Answer

2ndValue

Answer

my-var

Question 13

A developer writes a method that reads a file and parses its contents. Which exception handling approach is best practice for ensuring the file is properly closed even if an exception occurs?

Accepted Answer

Use a try-with-resources statement.. The try-with-resources statement automatically closes any resource that implements AutoCloseable (such as FileReader or BufferedReader) at the end of the statement, regardless of whether an exception occurs. This eliminates the risk of resource leaks and is the recommended best practice in Java for handling resources that must be closed.

Answer

Use a throws clause and let the caller handle closing.

Answer

Use a try-catch block and close the resource in the catch block.

Answer

Use a try-catch block and close the resource in the finally block.

Question 14

A team is developing a financial application that processes large arrays of market data. They have a method that calculates moving averages by copying a subarray for each window. The current implementation creates a new array for each window using System.arraycopy. The application is running slowly in production. The team identifies that the method is called millions of times per minute. The array is large and the window size is small. The garbage collector overhead is high due to many short-lived arrays. Which optimization should they apply to reduce object creation and improve performance?

Accepted Answer

Use a single temporary array and reuse it by copying data into it for each window.. Reusing a single temporary array eliminates the repeated allocation of short-lived arrays for each window, directly reducing garbage collector overhead. The current implementation uses System.arraycopy to create a new array per window, which is the primary source of object churn. By allocating one array once and copying data into it for each window, the team minimizes object creation while still performing the necessary copy operation.

Answer

Use a Stream to process the array without creating intermediate arrays.

Answer

Use Arrays.copyOfRange() which is faster than System.arraycopy.

Answer

Use ArrayList instead of array to avoid copy.

Question 15

A developer writes: int x = 5; int y = x++ + ++x; What is the value of y after execution?

Accepted Answer

12. The expression `int y = x++ + ++x;` involves post-increment and pre-increment operators. Initially, `x = 5`. In `x++`, the current value (5) is used, then `x` becomes 6. In `++x`, `x` is incremented to 7, then the new value (7) is used. So, `y = 5 + 7 = 12`. Option A is correct.

Answer

11

Answer

10

Answer

Compilation error

Question 16

Which two control flow statements can be used to terminate a loop prematurely?

Accepted Answer

return. Options A (return) and D (break) are correct. The return statement terminates the enclosing method, thereby ending the loop. The break statement directly terminates the innermost loop. Option B (exit) is not a Java statement; System.exit() is a method but it is not a control flow statement for loop termination. Option C (System.gc()) is a garbage collection hint and does not affect loop control. Option E (continue) skips the current iteration but does not terminate the loop.

Answer

exit

Answer

System.gc()

Answer

continue

Question 17

A method 'public static int findMax(int[] numbers)' returns the maximum value in the array. Which implementation correctly handles an empty array by returning 0?

Accepted Answer

if(numbers.length == 0) return 0; int max = numbers[0]; for(int i=1; i<numbers.length; i++) if(numbers[i] > max) max = numbers[i]; return max;. Ly handles an empty array by checking `numbers.length == 0` and returning 0 before attempting to access `numbers[0]`, which would throw an `ArrayIndexOutOfBoundsException` on an empty array. It then initializes `max` to the first element and iterates from index 1, ensuring all elements are compared correctly even if all numbers are negative.

Answer

int max = 0; for(int n: numbers) if(n > max) max = n; return max;

Answer

int max = numbers[0]; for(int i=1; i<numbers.length; i++) if(numbers[i] > max) max = numbers[i]; return max;

Answer

if(numbers.length == 0) return 0; int max = 0; for(int n: numbers) if(n > max) max = n; return max;

Question 18

What is the result of: Integer a = null; int b = (a != null) ? a : 0; System.out.println(b);

Accepted Answer

0. The ternary operator evaluates the condition (a != null). Since a is null, the condition is false, so the expression returns the second operand, which is the int literal 0. This value is assigned to int b, and System.out.println(b) prints 0. No NullPointerException occurs because the ternary operator never attempts to unbox a null reference.

Answer

NullPointerException

Answer

Compilation error

Answer

null

Question 19

A class defines a static variable initialized at declaration: static int count = 10;. A static method attempts to modify it: count = 20;. Which statement is true?

Accepted Answer

The variable can be changed to 20. Static variables belong to the class, not instances, and can be accessed and modified by static methods. The assignment `count = 20;` is valid and changes the value from 10 to 20 at runtime.

Answer

The variable cannot be accessed from a static method

Answer

The code causes a compilation error

Answer

The variable is read-only

Question 20

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