1Z0-811 Practice Test 15 — 15 Questions

Question 1

A developer writes: int x; System.out.println(x); What is the result?

Accepted Answer

Compilation fails. B is correct because in Java, a local variable (such as `int x;` declared inside a method) must be initialized before it is used. The code attempts to print `x` without assigning a value, which violates the definite assignment rule and causes a compilation error.

Answer

null

Answer

Runtime error

Answer

0

Question 2

Arrange the steps to use the Scanner class to read user input in Java in the correct order.

Accepted Answer

1. Import java.util.Scanner; 2. Create Scanner object: Scanner sc = new Scanner(System.in); 3. Prompt user: System.out.print("Enter value: "); 4. Read input: String input = sc.nextLine(); 5. Close scanner: sc.close();. First import Scanner, then create an instance, prompt user, read input, and finally close the scanner.

Answer

1. Create Scanner object: Scanner sc = new Scanner(System.in); 2. Import java.util.Scanner; 3. Prompt user: System.out.print("Enter value: "); 4. Read input: String input = sc.nextLine(); 5. Close scanner: sc.close();

Answer

1. Import java.util.Scanner; 2. Prompt user: System.out.print("Enter value: "); 3. Create Scanner object: Scanner sc = new Scanner(System.in); 4. Read input: String input = sc.nextLine(); 5. Close scanner: sc.close();

Answer

1. Import java.util.Scanner; 2. Create Scanner object: Scanner sc = new Scanner(System.in); 3. Read input: String input = sc.nextLine(); 4. Close scanner: sc.close(); 5. Prompt user: System.out.print("Enter value: ");

Question 3

What is printed by the program?

```java
for (int i = 0; i < 2; i++) {
    for (int j = 0; j < 3; j++) {
        System.out.print(i + "," + j + " ");
        if (i == 1) break;
    }
}
```

Accepted Answer

0,0 0,1 0,2 1,0. The program uses nested for loops. The outer loop runs with i from 0 to 1 (inclusive). For each i, the inner loop runs with j from 0 to 2 (inclusive). However, the inner loop contains a break statement that executes when i equals 1, causing the inner loop to terminate after printing the first pair for i=1 (1,0). Thus, the output is: 0,0 0,1 0,2 1,0. The outer loop then increments i to 2, but the condition i < 2 fails, so the program ends.

Answer

0,0 0,1 0,2

Answer

0,0 0,1 0,2 1,0 1,1 1,2 2,0 2,1 2,2

Answer

0,0 0,1 0,2 1,0 1,1

Question 4

Which THREE are valid ways to declare and initialize an integer variable in Java? (Choose three.)

Accepted Answer

int x = 1_000;. Java allows underscores in numeric literals (introduced in Java 7) to improve readability, and `1_000` is a valid integer literal representing 1000. The compiler simply ignores the underscores during parsing.

Answer

int x = 2.0;

Answer

int x = 0xG;

Question 5

A financial trading application processes a batch of 10 million trade transactions every night. Each transaction is a String containing trade details such as ID, symbol, quantity, and price. The current implementation uses string concatenation with the += operator in a loop to build a summary report string. The application frequently runs out of memory and takes hours to complete. The server has 16 GB of RAM and runs Java 11. The code cannot be restructured significantly due to regulatory requirements, but performance improvements are allowed. Which course of action will most effectively resolve the performance and memory issues?

Accepted Answer

Replace the String concatenation with StringBuilder.. The performance and memory issues are caused by using String concatenation (+=) inside a loop, which creates many intermediate String objects because Strings are immutable in Java. StringBuilder is mutable and designed for efficient string concatenation without creating intermediate objects, making it the optimal solution. Option A (StringBuilder) is correct. Option B (calling intern()) would not improve performance and could degrade it. Option C (increasing heap size) only postpones the OutOfMemoryError and does not fix the inefficiency. Option D (StringBuffer) is thread-safe but slower due to synchronization; it is unnecessary in this single-threaded context. Therefore, replacing concatenation with StringBuilder is the most effective resolution.

Answer

Call intern() on the concatenated result at each iteration.

Answer

Increase the JVM heap size to 32 GB to accommodate the temporary string objects.

Answer

Replace the String concatenation with StringBuffer.

Question 6

Which loop is guaranteed to execute its body 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 Java, the do-while loop syntax is `do { ... } while (condition);`.

Answer

repeat-until loop

Answer

while loop

Answer

for loop

Question 7

Match each Java operator to its description.

Accepted Answer

==: Compares two values for equality. The correct matches are: == for equality, && for logical AND. Common confusions include mixing assignment (=) with comparison (==) and misunderstanding the ternary operator vs. logical operators.

Answer

!=: Used to assign a value to a variable

Answer

instanceof: Used to compare two primitive values

Answer

?:: Used to perform a logical OR operation

Question 8

A banking application has a base class 'Account' with a method 'withdraw()' marked as final. A subclass 'SavingsAccount' tries to override 'withdraw()'. What is the outcome?

Accepted Answer

Compilation error because final methods cannot be overridden. In Java, a method marked as final cannot be overridden by a subclass. Any attempt to override a final method results in a compilation error. Therefore, the subclass SavingsAccount trying to override withdraw() will cause a compilation error.

Answer

The override works only if SavingsAccount is in the same package

Answer

The override succeeds, final is ignored in subclasses

Answer

Runtime error when the method is called

Question 9

A company's HR system uses an Employee class with sensitive salary information. The team wants to allow other classes to read the salary but not modify it. Which approach best preserves encapsulation?

Accepted Answer

Provide a public getSalary() getter method and keep salary private. Keeping the salary field private and exposing only a public getSalary() getter enforces encapsulation by preventing external classes from directly modifying the field. The getter provides read-only access, so other classes can retrieve the salary value without any ability to change it. This is the standard JavaBeans pattern for controlled attribute access and is exactly what the question asks for.

Answer

Declare the salary field as public

Answer

Create a private method that returns salary only when called from within the same package

Answer

Provide a public setSalary() setter method and keep salary private

Question 10

A developer wants to achieve loose coupling between components. Which two practices support loose coupling? (Choose two.)

Accepted Answer

Using interfaces to define contracts. Option C is correct because defining interfaces creates explicit contracts that decouple callers from concrete implementations, allowing components to depend on abstractions rather than specific classes and enabling substitution without code changes. Option D is correct because composition over inheritance lets an object delegate behavior to collaborating objects at runtime, so the composed parts can be swapped or mocked independently, reducing the tight compile-time coupling that deep inheritance hierarchies create. Option A is not appropriate because inheritance tightly binds a subclass to its superclass's implementation, so changes in the parent ripple into the child. Option B is not a coupling practice at all; encapsulation via private fields and public getters hides internal state but does not by itself reduce dependencies between components. Option E is not appropriate because extensive static methods create hard-coded, compile-time dependencies that are difficult to replace or test in isolation.

Answer

Using inheritance to share implementation

Answer

Using private fields with public getters

Answer

Using static methods extensively

Question 11

Which THREE statements are true about passing arrays to methods in Java?

Accepted Answer

Varargs parameters allow passing zero or more arguments of the specified type.. Option B is correct because a varargs parameter (declared as Type... name) accepts zero or more arguments of that type, and the compiler packages them into an array; the method can therefore be called with no arguments at all. Option D is correct because Java passes object references by value, so when an array is passed, the method receives a copy of the reference that points to the same underlying array object on the heap. Option E is correct because null is a valid value for any reference type, including arrays, so passing null as an array argument compiles fine (though dereferencing it at runtime would throw a NullPointerException). Option A is wrong because modifying array elements through the shared reference does affect the caller's array. Option C is wrong because reassigning the parameter to a new array only changes the local copy of the reference, leaving the caller's variable pointing to the original array.

Answer

If the method modifies elements of the array, the caller does not see the changes.

Answer

If the method assigns a new array to the parameter, the caller's variable is updated.

Question 12

Which THREE of the following expressions evaluate to true? (Assume int a=5, b=10)

Accepted Answer

a < b. The expression 'a < b' compares the integer values of a (5) and b (10). Since 5 is less than 10, the relational operator '<' returns the boolean value true.

Answer

a == b

Answer

a >= b

Question 13

Which TWO keywords are used for decision-making in Java? (Choose two.)

Accepted Answer

switch. The 'if' and 'switch' statements are both decision-making constructs in Java. 'if' evaluates a boolean expression to determine which block of code to execute, while 'switch' selects a block based on the value of an expression, typically an int, String, or enum. These are the two primary keywords for branching logic.

Answer

for

Answer

try

Answer

while

Question 14

Given int[] arr = {1,2,3}; which correctly creates a new array with length 5 and copies the contents of arr?

Accepted Answer

int[] newArr = Arrays.copyOf(arr, 5);. `Arrays.copyOf(int[] original, int newLength)` creates a new array of the specified length (5) and copies the elements from the original array into it, padding with default values (0 for int) for any extra positions. This method is specifically designed for this task, ensuring the original array remains unchanged.

Answer

int[] newArr = new int[5]; newArr = arr;

Answer

int[] newArr = arr.clone(); newArr.length = 5;

Answer

int[] newArr = Arrays.copy(arr, 5);

Question 15

A developer writes the following code: String s1 = "Hello"; String s2 = "Hello"; System.out.println(s1 == s2); What is the output?

Accepted Answer

true. String literals in Java are interned, meaning both s1 and s2 refer to the same String object in the string constant pool. The == operator compares object references, not content, so since both variables point to the same interned string, the comparison yields true.

Answer

Compilation fails

Answer

false

Answer

Hello