1z0-830 Exam Dumps - Java SE 21 Developer Professional

In Java, a lambda expression can have two forms for its body:

Single Expression:A concise form where the body consists of a single expression. The result of this expression is implicitly returned.

Example:

java

(a, b) -> a + b

In this example, (a, b) are the parameters, and a + b is the single expression that adds them together.

Statement Block:A more detailed form where the body consists of a block of statements enclosed in braces {}. Within this block, you can have multiple statements, and if a return value is expected, you must explicitly use the return statement.

Example:

java

(a, b) -> {

int sum = a + b;

System.out.println("Sum is: " + sum);

return sum;

}

In this example, the lambda body is a statement block that performs multiple actions: it calculates the sum, prints it, and then returns the sum.

Given the options:

A. Two statements:While a lambda body can contain multiple statements, they must be enclosed within a statement block {}. Simply having two statements without braces is not valid syntax for a lambda expression.

B. An expression and a statement:Similar to option A, if a lambda body contains more than one element (be it expressions or statements), they need to be enclosed in a statement block.

C. A statement block:This is correct. A lambda expression can have a body that is a statement block, allowing multiple statements enclosed in braces.

D. None of the above:This is incorrect since option C is valid.

E. Two expressions:As with options A and B, multiple expressions must be enclosed in a statement block to form a valid lambda body.

Therefore, the correct answer is C: A statement block.

In Java's java.nio.file package, the Path class represents a file path in a file system. The Paths.get(String first, String... more) method is used to create a Path instance by converting a path string or URI.

In the provided code snippet, the Path object path is created with the string "C:\\home\\joe\\foo". This represents an absolute path on a Windows system.

The getName(int index) method of the Path class returns a name element of the path as a Path object. The index is zero-based, where index 0 corresponds to the first element in the path's name sequence. It's important to note that the root component (e.g., "C:\" on Windows) is not considered a name element and is not included in this sequence.

Therefore, for the path "C:\\home\\joe\\foo":

Root Component:"C:\"

Name Elements:

Index 0: "home"

Index 1: "joe"

Index 2: "foo"

When path.getName(0) is called, it returns the first name element, which is "home". Thus, the output of the System.out.println statement is home.

In this code, three static methods from the Boolean class are used: logicalAnd, logicalOr, and logicalXor. Each method takes two boolean arguments and returns a boolean result based on the respective logical operation.

Evaluation of Each Statement:

Boolean.logicalAnd(1 == 1, 2 < 1)

Operands:

1 == 1 evaluates to true.

2 < 1 evaluates to false.

Operation:

Boolean.logicalAnd(true, false) performs a logical AND operation.

The result is false because both operands must be true for the AND operation to return true.

Output:

System.out.print(false); prints false.

Boolean.logicalOr(1 == 1, 2 < 1)

Operands:

1 == 1 evaluates to true.

2 < 1 evaluates to false.

Operation:

Boolean.logicalOr(true, false) performs a logical OR operation.

The result is true because at least one operand is true.

Output:

System.out.print(true); prints true.

Boolean.logicalXor(1 == 1, 2 < 1)

Operands:

1 == 1 evaluates to true.

2 < 1 evaluates to false.

Operation:

Boolean.logicalXor(true, false) performs a logical XOR (exclusive OR) operation.

The result is true because exactly one operand is true.

Output:

System.out.print(true); prints true.

Combined Output:

Combining the outputs from each statement, the final printed result is:

nginx

falsetruetrue

In this scenario, we have a Person class that extends ListResourceBundle and a properties file named Person.properties. Both define a resource with the key "name" but with different values:

Person class (ListResourceBundle):Defines the key "name" with the value "Jeanne".

Person.properties file:Defines the key "name" with the value "James".

When the ResourceBundle.getBundle("Person") method is called, the Java runtime searches for a resource bundle with the base name "Person". The search order is as follows:

Class-Based Resource Bundle:The runtime first looks for a class named Person (i.e., Person.class).

Properties File Resource Bundle:If the class is not found, it then looks for a properties file named Person.properties.

In this case, since the Person class is present and accessible, the runtime will load the Person class as the resource bundle. Therefore, the getBundle method returns an instance of the Person class.

Subsequently, when bundle.getString("name") is called, it retrieves the value associated with the key "name" from the Person class, which is "Jeanne".

Thus, the output of the program is:

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Jeanne

In this program, the following operations are performed:

Paths Initialization:

Path p1 is set to "f1.txt".

Path p2 is set to "f2.txt".

File Move Operation:

Files.move(p1, p2); attempts to move (or rename) f1.txt to f2.txt.

File Delete Operation:

Files.delete(p1); attempts to delete f1.txt.

Analysis:

If f1.txt Does Not Exist:

The Files.move(p1, p2); operation will throw a NoSuchFileException because the source file f1.txt is missing.

If f1.txt Exists and f2.txt Does Not Exist:

The Files.move(p1, p2); operation will successfully rename f1.txt to f2.txt.

Subsequently, the Files.delete(p1); operation will throw a NoSuchFileException because p1 (now f1.txt) no longer exists after the move.

If Both f1.txt and f2.txt Exist:

The Files.move(p1, p2); operation will throw a FileAlreadyExistsException because the target file f2.txt already exists.

If f2.txt Exists While f1.txt Does Not:

Similar to the first scenario, the Files.move(p1, p2); operation will throw a NoSuchFileException due to the absence of f1.txt.

In all possible scenarios, an exception is thrown during the execution of the program.

In Java, the ConcurrentHashMap class provides several constructors that allow for the customization of its initial capacity, load factor, and concurrency level. To configure a ConcurrentHashMap with an initial capacity of 42 and a concurrency level of 10, you can use the following constructor:

java

public ConcurrentHashMap(int initialCapacity, float loadFactor, int concurrencyLevel)

Parameters:

initialCapacity: The initial capacity of the hash table. This is the number of buckets that the hash table will have when it is created. In this case, it is set to 42.

loadFactor: A measure of how full the hash table is allowed to get before it is resized. The default value is 0.75, but in this case, it is set to 0.88.

concurrencyLevel: The estimated number of concurrently updating threads. This is used as a hint for internal sizing. In this case, it is set to 10.

Therefore, to create a ConcurrentHashMap with an initial capacity of 42, a load factor of 0.88, and a concurrency level of 10, you can use the following code:

java

var concurrentHashMap = new ConcurrentHashMap<>(42, 0.88f, 10);

Option Evaluations:

A. var concurrentHashMap = new ConcurrentHashMap(42);: This constructor sets the initial capacity to 42 but uses the default load factor (0.75) and concurrency level (16). It does not meet the requirement of setting the concurrency level to 10.

B. None of the suggestions.: This is incorrect because option E provides the correct configuration.

C. var concurrentHashMap = new ConcurrentHashMap();: This uses the default constructor, which sets the initial capacity to 16, the load factor to 0.75, and the concurrency level to 16. It does not meet the specified requirements.

D. var concurrentHashMap = new ConcurrentHashMap(42, 10);: This constructor sets the initial capacity to 42 and the load factor to 10, which is incorrect because the load factor should be a float value between 0 and 1.

E. var concurrentHashMap = new ConcurrentHashMap(42, 0.88f, 10);: This correctly sets the initial capacity to 42, the load factor to 0.88, and the concurrency level to 10, meeting all the specified requirements.

Therefore, the correct answer is option E.

Analyzing the thrower() Method Execution

java

int i = 0;

return i / i;

i / i evaluates to 0 / 0, whichthrows ArithmeticException (/ by zero).

Since catch (NumberFormatException e) doesnot matchArithmeticException, it is skipped.

The finally block always executes, printing:

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Beaujolais Nouveau,

The exceptionpropagates backto main().

Handling the Exception in main()

java

try {

thrower();

System.out.print("Dom Pérignon, ");

} catch (Exception e) {

System.out.print("Chablis, ");

} finally {

System.out.print("Saint-Émilion");

}

Since thrower() throws ArithmeticException, it is caught by catch (Exception e).

"Chablis, "is printed.

Thefinally block always executes, printing "Saint-Émilion".

Final Output

nginx

Beaujolais Nouveau, Chablis, Saint-Émilion

Thus, the correct answer is:Beaujolais Nouveau, Chablis, Saint-Émilion

References:

Java SE 21 - Exception Handling

Java SE 21 - finally Block Execution

The var keyword and identifier rules:

The var keyword is used for local variable type inference introduced inJava 10.

However,Java does not allow _ (underscore) as an identifiersinceJava 9.

If we try to use _ as a variable name, the compiler will throw an error:

pgsql

error: as of release 9, '_' is a keyword, and may not be used as an identifier

The $ symbol as an identifier:

The $ characteris a valid identifierin Java.

However, since _ is not allowed, the codefails to compile before even reaching $.

Thus,the correct answer is "Compilation fails."

References:

Java SE 21 - var Local Variable Type Inference

Java SE 9 - Restrictions on _ Identifier