1Z0-811 Practice Test 3 — 25 Questions

Question 1

A developer uses a switch statement with a String variable. Which is true about this usage?

Accepted Answer

It works with strings starting from Java 7. Starting from Java 7 (JSR 334), the switch statement supports String objects in addition to primitive types and enums. The compiler uses the `hashCode()` and `equals()` methods of the String class to evaluate the switch expression against case labels, making it a valid and efficient way to branch on string values.

Answer

It works only with primitive types

Answer

It causes a compilation error because strings are not supported

Answer

It requires a default case

Question 2

A developer writes: int a = 9; int b = 2; double result = a / b; System.out.println(result); What is the output?

Accepted Answer

4.0. (4.0). In Java, when dividing two integers, the result is integer division, which truncates the fractional part. So 9 / 2 yields 4 (int). This int value is then assigned to a double variable, resulting in 4.0. Option A (4) would be the result of printing an int, but since result is double, it prints 4.0. Option C is incorrect because the code compiles fine. Option D is incorrect because 4.5 would require at least one operand to be double (e.g., a / (double)b).

Answer

4

Answer

Compilation error

Answer

4.5

Question 3

A developer writes a method that reads a file and processes its contents. The method uses a BufferedReader wrapped around a FileReader. Which of the following approaches ensures that both resources are properly closed even if an exception occurs?

Accepted Answer

Use try-with-resources with both resources declared in the try header.. Try-with-resources ensures that both the BufferedReader and FileReader are automatically closed in reverse order, even if an exception occurs. Option A is wrong because while it attempts to close both resources in separate try-catch blocks within a finally block, this approach is verbose and error-prone; if an exception occurs during the first close, the second close may be skipped unless handled carefully, and it does not guarantee resource closure as reliably as try-with-resources. Option C is wrong because closing only the BufferedReader may close the underlying FileReader due to chaining, but this approach lacks null-safety—if resource creation fails, a NullPointerException occurs when calling close, and it does not demonstrate proper exception handling or best practices. Option D is wrong because throwing a custom exception after closing resources does not ensure both are closed; it adds unnecessary complexity and may leave resources open if close methods throw exceptions.

Answer

Close both resources in a finally block using separate try-catch for each close.

Answer

Close only the BufferedReader in a finally block.

Answer

Throw a custom exception after closing resources in the catch block.

Question 4

During execution, the JVM uses Just-In-Time (JIT) compilation. What is its primary benefit?

Accepted Answer

Improves execution speed by compiling frequently used bytecode to native code.. JIT compilation improves execution speed by compiling frequently used bytecode into native machine code at runtime. Option A is incorrect because JIT does not translate bytecode into an intermediate language; it compiles to native code. Option C is incorrect because JIT compiles bytecode, not source code. Option D is incorrect because JIT's primary purpose is performance, not security.

Answer

Translates bytecode into an intermediate language for interpretation.

Answer

Converts Java source code directly into bytecode.

Answer

Enhances security by verifying bytecode integrity.

Question 5

A developer is writing a bitmask validation method. The method should return true if both input integers (x and y) have exactly the same least significant bit set. The developer writes: if (x & y == 1) { return true; } However, the condition never evaluates to true even when both numbers are odd (least significant bit = 1). Debugging shows that x and y are positive integers. What is the root cause and the correct fix?

Accepted Answer

Add parentheses: if ((x & y) == 1) { ... }. In Java, the bitwise AND operator & has lower precedence than the equality operator ==. So x & y == 1 is parsed as x & (y == 1), which first evaluates y == 1 to a boolean, then performs bitwise AND with x, treating true as 1 and false as 0. That's not the intended check. The correct fix is to add parentheses to ensure & is evaluated first: (x & y) == 1. This checks if both numbers have the same least significant bit set (both odd). Option B correctly adds parentheses. Options A, C, and D do not correctly address the bitwise check: A uses modulo which works for odd/even but not general bitmasking; C uses bitwise OR which checks if either bit is set; D uses logical AND which is for booleans, not integers.

Answer

Use modulo: if (x % 2 == 1 && y % 2 == 1) { ... }

Answer

Use bitwise OR: if (x | y == 1) { ... }

Answer

Use logical AND: if (x && y == 1) { ... }

Question 6

What is the primary role of the Java Development Kit (JDK) compared to the JRE?

Accepted Answer

JDK includes compilers and tools for developing Java applications.. The JDK (Java Development Kit) is a software development environment used for developing Java applications. It includes the JRE (Java Runtime Environment) plus development tools such as the Java compiler (javac), debugger, and other utilities. In contrast, the JRE provides only the runtime environment needed to run Java applications. Therefore, option D is correct because the JDK includes compilers and tools for development. Option A is incorrect because the JDK provides far more than just a debugger and profiler; it includes the compiler and other essential tools. Option B is incorrect because the JDK includes the JRE, not the other way around. Option C is incorrect because the JRE is required to run Java applications, while the JDK is needed for development; the JDK is not required to run applications.

Answer

JDK provides only a debugger and profiler.

Answer

JRE includes the JDK and additional libraries.

Answer

JDK is required to run Java applications, whereas JRE is not.

Question 7

A developer writes a class 'Vehicle' with a method 'move()' that prints 'Vehicle moves'. A subclass 'Car' overrides 'move()' to print 'Car moves'. Given: Vehicle v = new Car(); v.move(); What is the output?

Accepted Answer

Car moves. Java uses dynamic method dispatch (runtime polymorphism). Even though the reference variable is of type 'Vehicle', the actual object is a 'Car' instance. At runtime, the JVM calls the overridden 'move()' method of the 'Car' class, printing 'Car moves'.

Answer

Vehicle moves

Answer

Runtime exception

Answer

Compilation fails

Question 8

Which TWO of the following are valid benefits of using inheritance in Java? (Choose two.)

Accepted Answer

Allows polymorphic behavior. Options B and C are correct. Inheritance promotes code reuse by allowing subclasses to reuse fields and methods from superclasses, reducing redundancy. It also enables polymorphic behavior through method overriding, allowing objects to be treated as instances of their parent class. Option A is incorrect because inheritance actually increases coupling between classes, which is generally considered a disadvantage, not a benefit. Option D is incorrect because encapsulation is enforced through access modifiers (private, protected, public), not inheritance. Option E is incorrect because inheritance can actually complicate debugging by introducing dependencies across classes.

Answer

Increases coupling between classes

Answer

Enforces encapsulation

Answer

Simplifies debugging

Question 9

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

Accepted Answer

boolean. (boolean) is correct because boolean is one of the eight primitive data types in Java, representing a single bit of information with only two possible values: true or false. It is not an object and does not have methods, unlike reference types such as Boolean (the wrapper class).

Answer

void

Answer

String

Question 10

Which three statements about String immutability are true? (Choose three)

Accepted Answer

The intern() method returns a String from the pool. The `intern()` method returns a canonical representation of the string from the string pool, ensuring that strings with the same content share the same memory reference, which is a key aspect of immutability and memory optimization in Java.

Answer

String objects can be modified after creation

Answer

String objects can be changed by calling methods

Question 11

Given the code snippet: 'int[] nums = {10, 20, 30, 40}; int sum = 0; for (int i = 0; i < nums.length; i++) { sum += nums[i]; }'. What is the value of sum after execution?

Accepted Answer

100. (100) because the for loop iterates over each element of the array {10, 20, 30, 40} and adds it to the sum variable. The sum starts at 0, and after adding 10, 20, 30, and 40, the total becomes 100.

Answer

30

Answer

60

Answer

140

Question 12

A method 'public static void modify(int[][] matrix) { matrix[0][0] = 99; }' is called with 'int[][] values = {{1,2},{3,4}}; modify(values);'. What is the value of values[0][0] after the call?

Accepted Answer

99. Java passes object references by value. When 'modify(values)' is called, the reference to the 2D array is copied into the method parameter 'matrix'. Since 'matrix' points to the same array object, modifying 'matrix[0][0]' directly changes the original array's element, so 'values[0][0]' becomes 99.

Answer

Exception

Answer

1

Answer

0

Question 13

Given the code:

int[] a = {1, 2, 3};
int[] b = {4, 5};
a = b;
b[0] = 99;
System.out.println(a[0]);

What is the output?

Accepted Answer

99. After `a = b;`, both `a` and `b` reference the same array object. Modifying `b[0]` to 99 also changes `a[0]` because they share the same underlying array. Therefore, `a[0]` prints 99.

Answer

3

Answer

1

Answer

4

Question 14

Which TWO methods correctly modify the passed array in place?

Accepted Answer

public void zeroOut(int[] a) { for (int i = 0; i < a.length; i++) a[i] = 0; }. It directly modifies each element of the passed array by assigning 0 to a[i] within the loop. In Java, when an array is passed to a method, the method receives a reference to the same array object, so changes to the array's elements are reflected in the caller's array.

Answer

public void reset(int[] a) { a = new int[10]; }

Answer

public void swap(int[] a) { int[] temp = a; a = new int[1]; a[0] = temp[0]; }

Answer

public void setFirst(int[][] a) { a = new int[1][1]; a[0][0] = 5; }

Question 15

A developer needs to store a currency value with two decimal places. Which primitive type is most appropriate?

Accepted Answer

double. (double) is the most appropriate primitive type for storing a currency value with two decimal places because double is a 64-bit IEEE 754 floating-point type that can represent fractional values with sufficient precision for typical monetary amounts. While float (32-bit) could also store decimals, double provides higher precision (15-16 significant digits) and is the default type for decimal literals in Java, making it the standard choice for currency calculations in the exam context.

Answer

float

Answer

long

Answer

int

Question 16

Arrange the steps to create and use a simple Java inheritance hierarchy in the correct order.

Accepted Answer

Create the superclass, then create the subclass with extends, then override methods if needed, then add new members, then use the subclass.. First create the superclass, then create subclass with extends, override methods if needed, add new members, and then use the subclass.

Answer

Create the subclass, then create the superclass, then override methods, then add new members, then use the subclass.

Answer

Create the superclass, then create the subclass with extends, then add new members, then override methods, then use the subclass.

Answer

Create the superclass, then create the subclass without using extends (copy code), then override methods, then add new members, then use the subclass.

Question 17

A developer writes a method that reads a file and must ensure the file is closed even if an exception occurs. Which construct should be used?

Accepted Answer

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, even if an exception occurs. This eliminates the need for explicit cleanup code and ensures deterministic resource management without relying on a `finally` block.

Answer

A throws declaration in the method signature

Answer

A finally block without any resource declaration

Answer

A try-catch-finally block with explicit close in finally

Question 18

Consider the following code snippet: 
public int getValue() {
    try {
        return 1;
    } catch (Exception e) {
        return 2;
    } finally {
        return 3;
    }
}
What does the method return?

Accepted Answer

3. (3) because a `finally` block always executes after the `try` block, and if the `finally` block contains a `return` statement, that return value overrides any return value from the `try` or `catch` blocks. In Java, the `finally` block's `return` statement causes the method to exit with the value 3, regardless of what the `try` block attempted to return.

Answer

The code does not compile.

Answer

2

Answer

1

Question 19

What does the java command with -jar option do?

Accepted Answer

Executes a JAR file by reading its manifest. The `java -jar` command executes a JAR file by reading the `Main-Class` entry from the JAR's manifest file (`META-INF/MANIFEST.MF`). This tells the Java launcher which class contains the `public static void main(String[] args)` method to start the application. It does not compile, list, or create JAR files.

Answer

Compiles Java files inside the JAR

Answer

Lists contents of the JAR file

Answer

Creates a new JAR file

Question 20

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