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| Section | Objectives |
|---|---|
| Controlling Program Flow | - Apply decision statements and loops - Work with records and sealed classes - Use switch expressions and pattern matching |
| Collections and Generics | - Use sequenced collections and maps - Apply generics and bounded types - Use List, Set, Map, Queue, and Deque implementations |
| Java I/O and NIO | - Process file system resources - Read and write files - Use Path, Files, and related APIs |
| Annotations and JDBC | - Execute SQL operations and process results - Use built-in and custom annotations - Connect to databases using JDBC |
| Object-Oriented Programming | - Create and use classes, interfaces, enums, and records - Implement encapsulation and abstraction - Apply inheritance and polymorphism |
| Functional Programming | - Use lambda expressions and method references - Process data using Stream API - Work with functional interfaces |
| Exception Handling | - Create custom exceptions - Handle checked and unchecked exceptions - Use try-with-resources |
| Java Concurrency | - Create and manage threads - Use virtual threads - Work with concurrent collections and executors |
| Modules and Packaging | - Manage dependencies and exports - Create and use Java modules - Package and deploy applications |
| Handling Date, Time, Text, Numeric and Boolean Values | - Use date, time, duration, period, and localization APIs - Use String, StringBuilder, and related APIs - Work with primitive wrappers and number formatting |
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NEW QUESTION # 73
Which of the following statements oflocal variables declared with varareinvalid?(Choose 4)
Answer: A,B,C,E
Explanation:
1. Valid Use Cases of var
* var is alocal variable type inferencefeature.
* The compilerinfers the type from the assigned value.
* Example of valid use:
java
var a = 10; // Type inferred as int
var str = "Hello"; // Type inferred as String
2. Analyzing the Given Statements
Statement
Valid/Invalid
Reason
var a = 1;
Valid
Type inferred as int.
var b = 2, c = 3.0;
#Invalid
var doesnot allow multiple declarationsin one statement.
var d[] = new int[4];
#Invalid
Array brackets []are not allowedwith var.
var e;
#Invalid
varrequires an initializer(cannot be declared without assignment).
var f = { 6 };
#Invalid
{ 6 } is anarray initializer, which must have an explicit type.
var h = (g = 7);
Valid
g is assigned 7, and h gets its value.
Thus, the correct answers are:B, C, D, E
References:
* Java SE 21 - Local Variable Type Inference (var)
* Java SE 21 - var Restrictions
NEW QUESTION # 74
You are working on a module named perfumery.shop that depends on another module named perfumery.
provider.
The perfumery.shop module should also make its package perfumery.shop.eaudeparfum available to other modules.
Which of the following is the correct file to declare the perfumery.shop module?
Answer: A
Explanation:
* Correct module descriptor file name
* A module declaration must be placed inside a file namedmodule-info.java.
* The incorrect filename module-info.perfumery.shop.javais invalid(Option A).
* The incorrect filename module.javais invalid(Option C).
* Correct module declaration
* The module declaration must match the name of the module (perfumery.shop).
* The requires perfumery.provider; directive specifies that perfumery.shop depends on perfumery.
provider.
* The exports perfumery.shop.eaudeparfum; statement allows the perfumery.shop.eaudeparfum package to beaccessible by other modules.
* The incorrect syntax exports perfumery.shop.eaudeparfum.*; in Option A isinvalid, as wildcards (*) arenot allowedin module exports.
Thus, the correct answer is:File name: module-info.java
References:
* Java SE 21 - Modules
* Java SE 21 - module-info.java File
NEW QUESTION # 75
Which of the following java.io.Console methods doesnotexist?
Answer: C
Explanation:
* java.io.Console is used for interactive input from the console.
* Existing Methods in java.io.Console
* reader() # Returns a Reader object.
* readLine() # Reads a line of text from the console.
* readLine(String fmt, Object... args) # Reads a formatted line.
* readPassword() # Reads a password, returning a char[].
* readPassword(String fmt, Object... args) # Reads a formatted password.
* read() Does Not Exist
* Consoledoes not have a read() method.
* If character-by-character reading is required, use:
java
Console console = System.console();
Reader reader = console.reader();
int c = reader.read(); // Reads one character
* read() is available inReader, butnot in Console.
Thus, the correct answer is:read() does not exist.
References:
* Java SE 21 - Console API
* Java SE 21 - Reader API
NEW QUESTION # 76
Which of the following can be the body of a lambda expression?
Answer: D
Explanation:
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.
NEW QUESTION # 77
Given:
java
var now = LocalDate.now();
var format1 = new DateTimeFormatter(ISO_WEEK_DATE);
var format2 = DateTimeFormatter.ISO_WEEK_DATE;
var format3 = new DateFormat(WEEK_OF_YEAR_FIELD);
var format4 = DateFormat.getDateInstance(WEEK_OF_YEAR_FIELD);
System.out.println(now.format(REPLACE_HERE));
Which variable prints 2025-W01-2 (present-day is 12/31/2024)?
Answer: C
Explanation:
In this code, now is assigned the current date using LocalDate.now(). The goal is to format this date to the ISO week date format, which represents dates in the YYYY-'W'WW-E pattern, where:
* YYYY: Week-based year
* 'W': Literal 'W' character
* WW: Week number
* E: Day of the week
Given that the present day is December 31, 2024, this date falls in the first week of the week-based year 2025.
Therefore, the ISO week date representation would be 2025-W01-2, where '2' denotes Tuesday.
Among the provided formatters:
* format1: This line attempts to create a DateTimeFormatter using a constructor, which is incorrect because DateTimeFormatter does not have a public constructor that accepts a pattern directly. This would result in a compilation error.
* format2: This is correctly assigned the predefined DateTimeFormatter.ISO_WEEK_DATE, which formats dates in the ISO week date format.
* format3: This line attempts to create a DateFormat instance using a field, which is incorrect because DateFormat does not have such a constructor. This would result in a compilation error.
* format4: This line attempts to get a DateFormat instance using an integer field, which is incorrect because DateFormat.getDateInstance() does not accept such parameters. This would result in a compilation error.
Therefore, the only correct and applicable formatter is format2. Using format2 in the now.format() method will produce the desired output: 2025-W01-2.
NEW QUESTION # 78
......
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