1Z0-811 Practice Test 23 — 15 Questions

Question 1

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 2

A developer writes a method that accepts a variable number of int arguments and returns their product. Which method signature correctly implements this?

Accepted Answer

public static int product(int... nums). The syntax `int... nums` is the proper Java varargs syntax, allowing a method to accept zero or more `int` arguments, which are then treated as an array inside the method. This enables the developer to call `product(2, 3, 4)` or `product()` and compute the product by iterating over the array.

Answer

public static int product(int[] nums)

Answer

public static int product(int nums...)

Answer

public static int product(int... nums, int extra)

Question 3

Given two String objects s1 = "Hello" and s2 = "Hello", what does the expression (s1 == s2) return?

Accepted Answer

true. The `==` operator compares object references, not string content. Since both `s1` and `s2` are string literals, Java's string interning ensures they refer to the same `String` object in the string constant pool, so `s1 == s2` returns `true`.

Answer

Compilation error

Answer

false

Answer

It depends on the JVM

Question 4

What is the output of the program?

Accepted Answer

false. The program creates two StringBuilder objects with identical string content and compares them using the `equals()` method. Since the `StringBuilder` class does not override `Object.equals()`, it uses reference equality. The two objects are distinct instances, so `equals()` returns `false`. Therefore, the output is `false`.

Answer

10

Answer

true

Answer

20

Question 5

A novice developer wrote a condition: if (x = 10) { ... } What is the result?

Accepted Answer

Compilation error. In Java, the assignment operator `=` is used to assign a value, not to compare values. The condition `if (x = 10)` attempts to assign 10 to `x` within an `if` statement, which is not a boolean expression. Java requires the condition in an `if` statement to evaluate to a `boolean`, so this code will not compile. Option D is correct because the compiler will report an error, typically stating 'incompatible types: int cannot be converted to boolean'.

Answer

The condition always evaluates to true

Answer

It executes the block if x equals 10

Answer

Runtime exception thrown

Question 6

Which THREE statements are true about interfaces in Java? (Choose three.)

Accepted Answer

An interface can extend multiple interfaces. Option B is correct because Java interfaces support multiple inheritance of type: an interface declaration may use the extends keyword followed by a comma-separated list of several interfaces, e.g. interface C extends A, B {}. Option C is correct because since Java 8 an interface may declare static methods (e.g. static int helper() { ... }), which belong to the interface itself and must be invoked via the interface name, not through an implementing instance. Option D is correct because since Java 8 an interface may declare default methods using the default keyword with a body, allowing implementations to inherit behavior without overriding it. Option A is not correct because interfaces are abstract types and cannot be instantiated with new; you must instantiate a concrete implementing class (or an anonymous class). Option E is not correct because every field declared in an interface is implicitly public static final, so private instance fields are not permitted (private methods are allowed since Java 9, but not private fields).

Answer

An interface can be instantiated directly

Answer

An interface can have private fields

Question 7

Which TWO statements are true about the Java programming language?

Accepted Answer

It is a strongly-typed language.. Option C is correct because Java is a statically and strongly-typed language: every variable and expression has a type known at compile time, and the compiler enforces type compatibility, rejecting implicit conversions that would lose precision (for example, assigning a double to an int without a cast). Option E is correct because Java's runtime (the JVM) performs automatic memory management via garbage collection, reclaiming heap objects that are no longer reachable so developers do not manually free memory. Option A is wrong because Java is fundamentally object-oriented (classes, inheritance, polymorphism), not purely procedural. Option B is wrong because Java deliberately omits direct pointer arithmetic and manipulation; references are managed by the JVM for safety and portability. Option D is wrong because Java permits only single inheritance of classes (a class extends exactly one superclass), though it does allow multiple inheritance of interfaces.

Answer

It is a purely procedural language.

Answer

It supports direct pointer manipulation for memory access.

Answer

It allows multiple inheritance of classes.

Question 8

When using try-with-resources, which interface must the resource implement?

Accepted Answer

AutoCloseable. The try-with-resources statement in Java requires that any resource declared in its parentheses implements the `AutoCloseable` interface (or its subinterface `Closeable`). This interface defines a single `close()` method, which the JVM automatically invokes at the end of the try block, ensuring proper resource management without needing an explicit `finally` block.

Answer

Serializable

Answer

Runnable

Answer

Comparable

Question 9

What is the default value of a boolean variable in Java?

Accepted Answer

false. In Java, the default value of a boolean variable (when declared as a class field or instance variable) is 'false'. This is specified by the Java Language Specification (JLS §4.12.5), which defines default values for all primitive types. Unlike local variables, which must be explicitly initialized, instance and static variables receive default values automatically.

Answer

null

Answer

true

Answer

0

Question 10

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

Accepted Answer

boolean. Option A (boolean) is correct because boolean is one of Java's eight built-in primitive types, holding only true or false values and occupying a JVM-defined size rather than being an object. Option B (double) is correct because double is a primitive type in Java, a 64-bit IEEE 754 floating-point value used for decimal numbers without requiring object instantiation. The remaining options are not primitives: Character and Integer are wrapper classes in java.lang that box the primitives char and int, while String is a class (not a primitive) representing immutable character sequences, so none of C, D, or E qualify.

Answer

Character

Answer

String

Answer

Integer

Question 11

Which three statements about arrays are correct? (Choose three.)

Accepted Answer

Arrays are objects in Java.. Option B is correct because in Java an array is a dynamically created object that extends Object, so it can be assigned to an Object reference and has members such as the length field. Option D is correct because a single array type can hold either primitive values (e.g., int[], double[]) or reference values to objects (e.g., String[], Object[]), though a given array holds only one component type. Option E is correct because Java array indexing is zero-based, meaning the first element is at index 0 and the last valid index is length - 1. Option A is incorrect because once an array is created its length is fixed and cannot be changed, although a variable can be reassigned to a different array. Option C is incorrect because array length need not be a compile-time constant; it can be determined at runtime, as in new int[n] where n is a variable.

Answer

The size of an array can change after creation.

Answer

The length of an array must be specified at compile time with a constant expression.

Question 12

Which TWO command-line tools are included in the Oracle JDK for monitoring and troubleshooting Java applications? (Select exactly 2)

Accepted Answer

jstack. jstack (A) is a JDK troubleshooting tool that prints Java thread stack traces, including locks and deadlock detection, for a running JVM, making it a core monitoring/diagnostic utility. jstat (C) is also a JDK monitoring tool that reports JVM statistics such as garbage collection, class loading, and JIT compilation performance via the jstatd/PerfData interface. jmod (B) is a packaging tool for creating and inspecting JMOD files, not for runtime monitoring. javap (D) is a class-file disassembler used to inspect bytecode and signatures, not to monitor a live JVM. jdb (E) is the Java Debugger for interactive debugging sessions, not a monitoring/troubleshooting statistics tool.

Answer

jmod

Answer

javap

Answer

jdb

Question 13

A developer wants to iterate over an array of integers named 'numbers'. Which loop declaration will correctly access each element?

Accepted Answer

for (int num : numbers). It uses the enhanced for-each loop syntax, which is designed specifically for iterating over arrays and collections in Java. The colon (:) separates the element variable declaration from the array name, and each iteration assigns the next element to 'num' automatically, without needing an index or explicit bounds checking.

Answer

for (int num = 0; num < numbers.length; num++)

Answer

for (int num in numbers)

Answer

for (int num : numbers.length)

Question 14

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

Accepted Answer

boolean. In Java, the primitive data types are the eight built-in value types defined by the language: byte, short, int, long, float, double, boolean, and char. Option B (boolean) is correct because it is a primitive type that holds only true or false values. Option C (int) is correct because it is a primitive 32-bit signed two's complement integer type. Option E (char) is correct because it is a primitive 16-bit Unicode character type. Option A (void) is not a data type at all; it is a keyword used only to indicate that a method returns no value. Option D (String) is not primitive because it is a reference type, specifically an instance of the java.lang.String class.

Answer

void

Answer

String

Question 15

Given the method: 'public static void swapFirstTwo(int[] arr) { int temp = arr[0]; arr[0] = arr[1]; arr[1] = temp; }'. What is the effect of calling this method with an array of length 1?

Accepted Answer

An ArrayIndexOutOfBoundsException is thrown.. The method accesses arr[0] and arr[1] without verifying the array length. When called with an array of length 1, index 1 is out of bounds because valid indices are 0 only. Java performs runtime bounds checking, so an ArrayIndexOutOfBoundsException is thrown.

Answer

The first element is swapped with itself.

Answer

A new array with length 2 is returned.

Answer

The array remains unchanged.