1Z0-811 Practice Test 1 — 25 Questions

Question 1

A developer is troubleshooting a performance issue in a reporting application. A nested loop iterates over a large dataset: the outer loop processes each row, and the inner loop performs a complex computation on each column. The application is taking longer than expected. Upon reviewing the code, the developer notices that the inner loop's termination condition is recalculated each iteration, which involves a costly method call. Which optimization should the developer implement to improve performance?

Accepted Answer

Move the inner loop's condition calculation outside the outer loop. Option B is correct because moving the condition calculation outside the outer loop (e.g., storing the result of the costly method call in a variable before the inner loop) eliminates redundant calls, improving performance. Option A is incorrect because using a break statement based on a precomputed value would not address the condition recalculation; the break would exit early but the condition is still recalculated each iteration unless moved outside. Option C is incorrect because converting to recursive calls would typically add overhead (stack frames) and is not a performance optimization for this specific issue. Option D is incorrect because simply changing to a while loop does not change the fact that the condition is recalculated each iteration; the costly method call would still be made each time unless the limit is precomputed.

Answer

Use the break statement to exit early based on a precomputed value

Answer

Convert the loops to recursive calls

Answer

Change the inner loop to use a while loop

Question 2

A developer writes: boolean b = !true && false; What is the value of b?

Accepted Answer

false. The expression `!true && false` is evaluated as `(!true) && false`, which is `false && false`. The logical AND (`&&`) operator returns `true` only if both operands are `true`; otherwise, it returns `false`. Therefore, `b` is assigned `false`. Option B is correct.

Answer

Compilation error: invalid operator.

Answer

NullPointerException

Answer

true

Question 3

Given: int a = 10; int b = 20; boolean flag = a++ > 10 && ++b > 20; What are the values of a and b after execution?

Accepted Answer

a=11, b=20. The expression `a++ > 10 && ++b > 20` uses short-circuit evaluation. Since `a++` is post-increment, the comparison uses the original value of `a` (10) before incrementing, so `10 > 10` is false. Because the left operand is false, the `&&` operator short-circuits and the right operand `++b > 20` is never evaluated. Therefore, `a` is incremented to 11, but `b` remains 20, making option D correct.

Answer

a=10, b=21

Answer

a=10, b=20

Answer

a=11, b=21

Question 4

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 5

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

Accepted Answer

char. Option C is correct because 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 6

A developer writes: for(int i=0; i<10; i++) { if(i%2==0) continue; System.out.print(i); }. What is the output?

Accepted Answer

13579. The loop iterates from i=0 to i=9. The `continue` statement skips the rest of the loop body when the condition `i%2==0` is true (i.e., when i is even). Therefore, only odd values of i (1, 3, 5, 7, 9) are printed, producing the output '13579'. Option B is correct.

Answer

0123456789

Answer

02468

Answer

123456789

Question 7

What is the result of: System.out.println(10 + 20 + "30");

Accepted Answer

3030. In Java, the '+' operator is left-associative. The expression `10 + 20 + "30"` is evaluated as `(10 + 20) + "30"`, which first performs integer addition to get `30`, then concatenates that integer with the string `"30"`, resulting in the string `"3030"`. The `System.out.println` method then prints the string `3030`.

Answer

102030

Answer

30

Answer

Compilation fails

Question 8

What is the output of the following code? int[] a = {1,2,3}; int[] b = a; b[0] = 99; System.out.println(a[0]);

Accepted Answer

99. Option C is correct because in Java, arrays are reference types. When `int[] b = a;` is executed, `b` does not create a new array; it simply references the same array object as `a`. Therefore, modifying `b[0]` directly changes the element in the original array `a`, so `a[0]` prints 99.

Answer

0

Answer

1

Answer

Compilation error

Question 9

Which TWO statements are true about interfaces in Java?

Accepted Answer

Interfaces can contain private methods.. Option A is correct because, since Java 9, interfaces can contain private methods to share common code between default methods or static methods within the interface, without exposing that logic to implementing classes. Option D is correct because all variables declared in an interface are implicitly public, static, and final, meaning they are constants that cannot be changed once assigned.

Answer

Interfaces can be instantiated.

Answer

Interfaces can contain constructors.

Answer

Interfaces cannot have default methods.

Question 10

Given: abstract class Shape { abstract void draw(); } class Circle extends Shape { void draw() {} } Which is true?

Accepted Answer

Circle must override draw(). Option B is correct because Circle is a concrete class that extends the abstract class Shape, which declares the abstract method draw(). A concrete subclass of an abstract class must provide an implementation for all inherited abstract methods, unless the subclass is also declared abstract. Circle provides an implementation of draw() with an empty body, which satisfies the override requirement.

Answer

Shape cannot have a constructor

Answer

Shape s = new Shape(); is valid

Answer

draw() must be public in Circle

Question 11

A method throws a checked exception. Which of the following is the correct way to handle it in the calling method?

Accepted Answer

Enclose the call in a try-catch block.. Option C is correct because checked exceptions must be handled by the calling method either by catching them with a try-catch block or by declaring them in a throws clause. Since the question asks for the correct way to handle it, enclosing the call in a try-catch block is a valid and direct handling approach that prevents the exception from propagating unhandled.

Answer

Ignore the exception since it is checked.

Answer

Add a throws clause to the calling method.

Answer

Use a finally block without catch.

Question 12

Given: int a = 9; int b = 2; double c = a / b; System.out.println(c); What is the output?

Accepted Answer

4.0. The expression `a / b` performs integer division because both operands are `int`. The result of `9 / 2` is `4` (the fractional part is truncated). This integer result is then implicitly widened to `double` when assigned to `c`, producing `4.0`. Therefore, the output is `4.0`.

Answer

4.5

Answer

4.0

Answer

4

Question 13

Match each access modifier to its visibility level.

Accepted Answer

private: Visible only within the same class. In Java, access modifiers control visibility: private (class-only), default (package), protected (package + subclasses), public (everywhere). Common mistakes include confusing private with default and protected with private.

Answer

private: Visible within the same package

Answer

protected: Visible only within the same class

Question 14

Match each Java collection interface to its characteristics.

Accepted Answer

List: Ordered collection (also known as sequence) that allows duplicate elements.. List is ordered and allows duplicates; Set is unordered and no duplicates; Queue is FIFO order; Map maps keys to values with unique keys. Common confusions include swapping List/Set characteristics or misidentifying Map as a collection of single elements.

Answer

Set: Ordered collection that allows duplicate elements.

Answer

Map: Collection of elements with no order and no duplicates.

Question 15

A developer runs the command shown in the exhibit. The developer wants to ensure the application uses the latest available language features. Which action should the developer take?

Accepted Answer

Download and install a newer version of the JDK.. Option A is correct because the latest available language features (e.g., pattern matching, sealed classes, records) are tied to the JDK version. Downloading and installing a newer JDK provides both the compiler (javac) and runtime (JVM) that support those features. Simply upgrading the JVM (Option D) or using -source/-target flags (Option C) does not enable new language syntax in the compiler if the JDK itself is outdated.

Answer

Enable lambda expressions by setting the -enable-lambdas flag.

Answer

Use the -source and -target flags to compile for a newer version.

Answer

Upgrade the JVM to the latest version.

Question 16

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

Question 17

Which THREE statements are true about the break and continue statements in Java? (Choose three.)

Accepted Answer

A labeled break can be used to exit an outer loop.. Option A is correct because a labeled break in Java allows you to specify a label on an outer loop and then use 'break label;' to exit that outer loop directly, not just the innermost loop. This is useful for breaking out of nested loops when a condition is met in an inner loop.

Answer

The continue statement can be used to exit a loop entirely.

Answer

The break statement cannot be used outside a loop.

Question 18

Given: boolean a = false; boolean b = true; boolean c = true; System.out.println(a || b && c); What is the output?

Accepted Answer

true. In Java, the logical AND operator (&&) has higher precedence than the logical OR operator (||). Therefore, the expression `a || b && c` is evaluated as `a || (b && c)`. Given `a = false`, `b = true`, and `c = true`, `b && c` evaluates to `true`, and then `false || true` evaluates to `true`. Thus, the output is `true`, making option D correct.

Answer

false

Answer

Compilation fails

Answer

None of the above

Question 19

Given: String str = "Java"; str = str.concat(" SE"); str.replace('a', 'A'); System.out.println(str); What is the output?

Accepted Answer

Java SE. Option C is correct because the `concat` method returns a new String "Java SE" which is assigned back to `str`. The `replace` method also returns a new String but its result is not assigned to any variable, so the original `str` remains unchanged. The final `println` outputs the current value of `str`, which is "Java SE".

Answer

Java

Answer

JAVA SE

Answer

JAvA SE

Question 20

What is the output of: int i = 1; i = i++; System.out.println(i);

Accepted Answer

1. Option D is correct because in Java, the expression `i = i++` uses the post-increment operator, which first stores the current value of `i` (1) for the assignment, then increments `i` to 2, but the stored original value (1) is then assigned back to `i`. Thus, `i` remains 1, and the output is 1.

Answer

Compilation fails

Answer

0

Answer

2