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Questions and Answers

What is the purpose of getters and setters in Java?

To provide methods for encapsulation and control access to private fields (correct)

To increase the complexity of class design

To directly access class fields without any restrictions

To avoid using constructors when creating objects

Which command is used to compile Java source files?

javadoc

javac (correct)

java

javap

What is an example of a non-numeric primitive cast in Java?

Casting a char to a String (correct)

Casting an int to a short

Casting a float to a long

Casting a double to an int

What is the purpose of the 'instanceof' operator in Java?

To check if an object is an instance of a particular class Signup and view all the answers

Which of the following is NOT a primitive data type in Java?

String Signup and view all the answers

What is the main function of the 'java' command?

To run Java applications Signup and view all the answers

How can you improve the readability of long numeric literals in Java?

By adding underscores Signup and view all the answers

Which of these data types consumes the least memory in Java?

byte Signup and view all the answers

What is the result of converting a float to an int in Java?

The decimal part is truncated Signup and view all the answers

What type of data can be stored in an Object reference in Java?

Primitive and non-primitive values Signup and view all the answers

Which component is responsible for generating documentation from Java source code?

javadoc Signup and view all the answers

What is the purpose of packaging documentation in Java?

To group related classes and interfaces together Signup and view all the answers

Which of the following is an example of a hexadecimal literal?

0x1A Signup and view all the answers

What is the primary purpose of using BufferedWriter?

To write data to a file using character streams Signup and view all the answers

Which of the following is a characteristic of the Scanner class?

It can parse primitive types and strings using regular expressions. Signup and view all the answers

What does deep copying involve when cloning objects?

Duplicating all objects referenced by the original object. Signup and view all the answers

What happens when a method in Java recurses too deeply?

It results in a StackOverflowError. Signup and view all the answers

In which scenario would you prefer using a Comparator over Comparable for sorting?

When you want to sort in multiple different ways without modifying the object. Signup and view all the answers

How does Java handle numeric overflow in floating-point operations?

It approximates the value to the nearest representable number. Signup and view all the answers

What function does the 'continue' statement serve in loops?

It allows execution to skip the current iteration and proceed to the next one. Signup and view all the answers

What is a common use of regular expressions in Java?

To validate or search strings for specific patterns. Signup and view all the answers

Which method is used to prevent NullPointerExceptions during auto-unboxing?

Checking for null before auto-unboxing. Signup and view all the answers

What is the role of 'default methods' in interfaces?

They allow interfaces to maintain backward compatibility. Signup and view all the answers

Which statement correctly reflects the use of enums in singletons?

Enums create thread-safe singleton instances automatically. Signup and view all the answers

What is the importance of manipulating paths in Java I/O?

To ensure cross-platform compatibility when dealing with file systems. Signup and view all the answers

What is the purpose of the 'compareTo' method in Java?

To sort collections directly without using a comparator. Signup and view all the answers

What is a primary advantage of using generics in Java?

Generics allow for type safety at compile-time. Signup and view all the answers

What does the diamond operator (<>) signify when declaring a generic type?

It specifies that type inference can be used. Signup and view all the answers

Which of the following best describes method overloading?

Defining multiple methods with the same name but different parameters. Signup and view all the answers

What is the purpose of a default method in Java interfaces?

To allow an implementation to be provided in the interface itself. Signup and view all the answers

Which statement about inheritance is true?

Inheritance promotes code reusability. Signup and view all the answers

How do inner classes access the members of their outer classes?

Directly without any special syntax. Signup and view all the answers

What is the significance of the ‘final’ keyword in Java?

It indicates that a variable cannot change after initialization. Signup and view all the answers

What does 'instanceof' allow you to do in Java?

Check if an object is of a specific type at runtime. Signup and view all the answers

What is the role of stream operations in Java?

Stream operations manipulate data in collections in a functional style. Signup and view all the answers

Which of the following statements about threading and collections is correct?

Thread-safe collections prevent concurrent access issues. Signup and view all the answers

What is the key difference between a List and a Set?

A List allows duplicate elements while a Set does not. Signup and view all the answers

Which type of nested class does not have a reference to its enclosing class?

Static nested class. Signup and view all the answers

When should you prefer using interface default methods?

To add new functionality to existing interfaces without breaking implementations. Signup and view all the answers

Study Notes

Getting Started with Java Language

Create a simple Java program using public class Main.
The main method is the entry point for Java programs.
System.out.println() prints text to the console.

Type Conversion

Cast numeric primitives between types, e.g., int to double.
Numeric promotion automatically converts smaller types to larger types during arithmetic operations.
Casting non-numeric primitives, such as char, boolean, or String, must be done explicitly.
Cast objects to specific subtypes using (Type) object.
Use instanceof to test if an object can be cast to a specific type prior to casting.

Getters and Setters

Use setters to modify object attributes and getters to retrieve their values.
Enforce value constraints by adding validation logic within setters.
Improve code maintainability and readability by providing a standardized interface for accessing object attributes.

Reference Data Types

Reference types store references to objects in memory.
Use the new keyword to instantiate an object.

The Java Compiler - 'javac'

Compile Java source code into bytecode using javac.
Use the -d option to specify the output directory for compiled classes.
Use the -cp option to specify the classpath for required libraries.
Use the -source flag to target a specific version of Java.

Documenting Java Code

Use Javadoc comments to generate documentation for your code.
Class documentation begins with /** and ends with */.
Method documentation includes descriptions, parameters, and return types.
Include links to relevant documentation using the {@link ...} tag.
Place code snippets within documentation using the {@code ...} tag.
Document class fields using /** ... */ above the field declaration.
Use inline code documentation for brief explanations within code blocks.

Command Line Argument Processing

Use args array in the main method to access command-line arguments.
Handle arguments individually or use libraries for easier parsing.

The Java Command - 'java' and 'javaw'

Run Java applications using the java command.
Specify the fully qualified class name containing the main method.
Use javaw to run Java applications without a console window.
Include library dependencies using the -cp (classpath) option.
Use Java options like -Xms and -Xmx to control memory allocation.
Escape spaces and special characters in command line arguments.
Execute JAR files directly using the java -jar command.
Run Java applications by specifying the "main" class.

Literals

Use underscores to improve readability of long numbers.
Use hexadecimal, octal, and binary literals.
Represent Boolean values with true and false.
Use string literals enclosed in double quotes.
Use null to represent the absence of a value.
Escape special characters within literals using backslashes.
Represent characters using single quotes.
Use decimal integer literals for whole numbers.
Represent floating-point numbers using decimal points and exponents.

Primitive Data Types

The char primitive type represents a single Unicode character.
Primitive Types Cheatsheet:
- boolean - Represents true or false values.
- byte - Holds an 8-bit signed integer.
- short - Holds a 16-bit signed integer.
- int - Holds a 32-bit signed integer.
- long - Holds a 64-bit signed integer.
- float - Represents a 32-bit single-precision floating-point number.
- double - Represents a 64-bit double-precision floating-point number.
The float primitive type represents a 32-bit single-precision floating-point number.
The int primitive type represents a 32-bit signed integer.
Convert primitives to other types using casting or type conversion methods.

Generics

Generics allow for type-safe code by accepting type parameters that can be specified at runtime.
? extends T acts as an upper bound, indicating the type parameter can be T or any subtype of T.
super T acts as a lower bound, indicating the type parameter can be T or any supertype of T.
Generic methods are declared similar to generic classes but with type parameters within the method signature.
To require multiple upper bounds on a type parameter, use the "extends A & B" syntax.
The Class.getGenericSuperclass() and Class.getGenericInterfaces() methods can be used to obtain the class that satisfies a generic parameter at runtime.
Generics improve code reusability and readability, reducing casting.
To instantiate a generic type, specify actual types for the type parameters.
A bounded generic class restricts type parameters to specific types or their subtypes.
The this keyword can be used to refer to the declared generic type within its declaration.
Generic parameters can be bound to more than one type, each binding to a distinct type.
Generics can help automatically cast objects to the correct type.
The instanceof operator can be used with generics to check the runtime type of an object with respect to a generic type.
Implementing a generic interface or extending a generic class can be done in various ways, including specifying type parameters in the implementation or subclass declaration.

Classes and Objects

Method overloading allows defining multiple methods with the same name but different parameter lists within a class.
Method overriding occurs in inheritance when a subclass provides a different implementation of a method inherited from its superclass.
Constructors are special methods called when a new object is created, initializing the object’s state.
Static final fields can be initialized using a static initializer block, which executes once when the class is loaded.
Object construction involves declaring a reference variable, creating an object using the new keyword followed by the constructor call, and assigning the object’s reference to the variable.
The simplest possible class contains a single method called main that serves as the entry point for the program.
An object member belongs to an instance of a class, while a static member belongs to the class itself.

Local Inner Class

A local inner class is defined within a method or block of code and has access to local variables of the enclosing method.

Nested and Inner Classes

A nested class is a class defined within another class.
Static nested classes are associated with the outer class but are not directly associated with its instances.
Non-static nested classes (inner classes) are associated with instances of the outer class and have access to all members (including private members) of the outer class.
Anonymous inner classes are unnamed classes that can be used to implement interfaces or extend classes. They create an implementation on the fly.
To create an instance of a non-static inner class from outside the outer class, an object of the outer class is needed.
Method local inner classes are defined within a method and have access to local variables of the enclosing method.
An inner class can access non-private members of the outer class directly, while private members are accessible through an object of the outer class.

The java.util.Objects Class

The Objects.nonNull() method reference can be used in stream API to filter and process non-null elements in a stream.
The Objects.isNull() method can be used to check if an object is null, simplifying null checks and enhancing clarity.

Default Methods

Default methods provide implementations for methods in interfaces, allowing for the extension of interfaces without breaking backward compatibility.
Implementing classes can access overridden default methods from the interface.
Default methods allow for the introduction of new functionalities to existing interfaces without requiring modifications to existing classes implementing the interface.

Packages

Packages allow for organizing classes and interfaces into logical groups.
Packages can be used to create classes with the same name without conflict.
Using package-protected scope restricts access to classes and members to the same package.

Inheritance

Inheritance enables creating new classes (subclasses) that inherit properties and behaviors from existing classes (superclasses).
Abstract classes cannot be instantiated directly but can be inherited and their abstract methods must be implemented by concrete subclasses.
The final keyword is used to prevent inheritance or method overriding.
The Liskov Substitution Principle states that subclasses should be able to replace their superclasses without altering the correctness of the program.
Abstract classes and interfaces both promote code reuse and polymorphism, but classes implement interfaces and inherit from abstract classes.
Abstract classes can have constructors, but these are only invoked when a concrete subclass is created.
Static inheritance is a concept where static members of a subclass can be accessed through the subclass type.
Programming to an interface encourages flexibility and promotes the use of polymorphism.
Overriding enables subclasses to provide specialized implementations of methods inherited from superclasses.
Variable shadowing occurs when a variable in a subclass has the same name as a variable in its superclass.
Narrowing assigns a subclass reference to a superclass reference, while widening does the opposite.
Static methods are not inherited.

Reference Types

Reference types define the type of an object that can be assigned to a variable.
Different reference types have different characteristics, such as immutable objects.

Console I/O

The Scanner class is used to read user input from the console.
The System.out.printf() method can be used to format strings in console output.
Implementing basic command-line behavior involves parsing input and performing actions based on user commands.

Streams

Streams provide a concise and powerful way to process sequences of data.
Streams can be consumed by performing operations on the elements and generating a result.
A frequency map can be created by collecting elements into a Map and counting their occurrences.
Infinite streams can generate an unlimited number of elements.
Streams can be collected into collections using the collect() method.
Streams can be used to implement mathematical functions, such as finding the sum or average of elements.
The flatMap() operation is used to flatten streams of nested elements.
Parallel streams allow for parallel processing of data to improve performance.
Streams can be created from various sources, such as arrays, collections, and files.
The statistics() method provides statistical information about numerical streams.
An iterator can be converted to a stream using the StreamSupport.stream() method.
An IntStream can be used to iterate over indexes in a stream.
Streams can be concatenated using the concat() method.
The reduce() operation is used to combine elements in a stream into a single value.
It is possible to preserve initial values after mapping a stream of Map.Entry.
An IntStream can be converted to a String using the mapToObj and collect methods.
The findFirst() method finds the first element in a stream that matches a predicate.
Streams and method references can be used to write self-documenting processes.
A Stream of Optional can be converted to a Stream of values.
It is possible to obtain a slice of a stream by using limit() and skip() methods.
A Map can be created based on a stream using the collect() method.
A stream can be joined to a single String using the Collectors.joining() method.
sorted() method can be used to sort a stream based on the elements.
Streams of primitives offer optimized operations for primitive data types.
Stream operations can be classified into categories such as intermediate and terminal operations.
The results of a stream can be collected into an array using the toArray() method.
Random strings can be generated using Streams and the Random class.

InputStreams and OutputStreams

Streams should be closed after use to release resources.
The InputStream can be read into a String using the BufferedReader class.
Input/Output streams can be wrapped to provide additional functionality, such as buffering.
The DataInputStream class can be used to read data in a stream.
The OutputStream can be used to write bytes to a file or other output destination.
An input stream can be copied to an output stream using the transferTo() method.

Readers and Writers

The BufferedReader class provides buffered reading from a character stream.
The StringWriter class allows for writing strings to a memory-based character stream.

Preferences

Preferences allow for storing application-specific data, such as user settings.
Event listeners can be added to track changes in preferences.
Sub-nodes of preferences can be accessed to organize data hierarchically.
Preferences can be coordinated across multiple application instances.
Preferences can be exported and imported.
Event listeners can be removed to stop receiving notifications.
Preferences values can be retrieved using the get() method.
Preferences values can be set using the put() method.

Collection Factory Methods

Factory methods provide a convenient way to create collections without explicitly specifying the implementation type.
Factory methods are available for Lists, Sets, and Maps.

Alternative Collections

Guava, Apache Collections, and Eclipse Collections provide alternative collections that offer enhanced functionality and performance.
Multimaps allow for mapping keys to multiple values.
HashBags, HashMultisets, and similar collections provide functionalities for managing collections of objects while maintaining counts for duplicate elements.
Collections can be compared for equality based on their elements.

Concurrent Collections

Concurrent collections are thread-safe, enabling safe access and modification by multiple threads.
Insertion into a ConcurrentHashMap happens concurrently, minimizing locking overhead.
Concurrent collections provide a way to manage data in multithreaded environments.

Choosing Collections

There are different collections each with different characteristics to be considered when making a choice.
A flowchart can be used to help choose the best collections based on specific use cases.

super Keyword

The super keyword refers to the superclass.
super can invoke constructors of the superclass or access inherited members with different implementations.

Serialization

Serialization allows for converting objects into byte streams for storage or transmission.
Basic serialization involves marking a class as Serializable and letting the default serialization mechanism handle the process.
Custom serialization enables controlling how an object is serialized and deserialized by implementing the writeObject and readObject methods.
Serialization can handle versioning and version compatibility using the serialVersionUID field.
Libraries like Gson and Jackson provide tools for serializing and deserializing objects to and from JSON format.

Optional

The Optional class represents a container that may or may not hold a value.
The isPresent() method can be used to check if the optional object contains a value.
The get() method retrieves the value if present, or throws an exception if the optional is empty.
The orElse(T other) method returns the value if present, or provides a default value.
The orElseThrow(Supplier<? extends X> exceptionSupplier) method throws an exception if the optional is empty.
The orElseGet(Supplier<? extends T> other) method lazily provides a default value if the optional is empty.
The filter(Predicate<? super T> predicate) method acts like a filter on the optional based on the predicate condition.
Optional classes can be used to hold primitive numeric types.
The ifPresent(Consumer<? super T> consumer) method executes the consumer action only if a value is present.
The flatMap(Function<? super T, Optional> mapper) method allows applying a function that returns an Optional object.

Object References

Object references are used as method parameters to pass objects by reference, enabling modification of the original object.

Exceptions and Exception Handling

Exceptions represent error conditions encountered during program execution.
The try-catch block is used to handle exceptions.
The try-with-resources statement ensures resources are properly closed, even if an exception occurs.
Custom exceptions can be defined to represent specific error conditions.
The InterruptedException exception can be caught when a thread’s execution is interrupted.
The return statements in a try-catch block can be placed in different locations based on the handling logic.
The Java exception hierarchy categorizes exceptions into checked and unchecked exceptions.
Stacktraces provide information about the chain of method calls leading to an exception.
The throw keyword is used to explicitly throw an exception.
Try-finally and try-catch-finally blocks are used to ensure specific code execution, like resource cleanup, regardless of exception occurrence.
The throws clause in a method declaration indicates which exceptions a method might throw.

Calendar and its Subclasses

The Calendar class represents a calendar system.
Calendar objects can be created using getInstance() or getCalendar() methods.
Calendar fields can be increased or decreased, such as adding days or months.
Subtracting calendars allows calculating time differences.
The get() method can be used to get the AM/PM indicator for a given time.

The static Keyword

The static keyword indicates a class-level member that belongs to the class itself and not to its instances.
Attempts to access a non-static member from a static context will result in a compilation error.
The static modifier can be used to declare fields as constants.

Properties Class

The Properties class is used to manage key-value pairs from property files.
Properties can be loaded from a property file using the load() method.
Properties can be saved as XML using the storeToXML() method.
Trailing whitespace in property files can cause issues, requiring careful handling.

Lambda Expressions

Lambda expressions are anonymous functions that can be used to implement functional interfaces.
Lambda expressions have a concise syntax and allow for passing behavior as arguments.
Lambda expressions can be used to implement a single abstract method of a functional interface.
Method references provide a concise way to refer to existing methods in a lambda expression.
Lambda expressions can be used to override multiple interface methods.
Lambda expressions are commonly used in event handling scenarios such as event listeners.
Lambda expressions in Java are effectively closures, allowing them to access variables from the enclosing scope.
Lambda expressions are typically smaller in memory footprint compared to anonymous inner classes.
Custom functional interfaces can be defined and used with Lambda expressions.
Lambda expressions can be used to convert code written in the traditional style into a more functional style.
The return keyword within a lambda expression returns from the lambda, not the outer method.
Lambda expressions enable using the “execute-around” pattern by providing a function that encapsulates the core logic.
Lambda expressions with predicates can be used to find specific elements within a collection.

Basic Control Structures

The switch statement allows for multiple case branches based on a value.
The do...while loop executes a block of code at least once and then continues iteration based on a condition.
The for each loop iterates over elements of a collection.
The continue statement skips the rest of the current iteration of a loop.
The if/else if/else block executes code conditionally based on Boolean expressions.
The for loop executes a code block repeatedly based on an initialization expression, a Boolean condition, and an update expression.
The ternary operator allows for a concise conditional expression that evaluates to one of two values.

Chapter 74: Control Flow

Break statement stops execution of the current loop and passes control to the statement following the loop.
While loop allows repetitive execution of a block of code as long as a certain condition is true.
If/Else statement provides a way to execute code based on certain logical conditions.
Nested break/continue can be used within loops to control the flow of execution.

Chapter 75: BufferedWriter

BufferedWriter allows writing lines of text to a file efficiently.

Chapter 76: New File I/O

Paths represent file and directory locations in the file system.
Paths can be manipulated using methods like resolve, getParent, and getFileName to navigate the file system.
Information about a path can be retrieved using methods like isAbsolute, getName, and getFileSystem.
Methods of the FileSystems class provide access to file system details, including root directories and supported file systems.
Reading files involves reading data from a file as bytes or characters.
Writing files involves creating or modifying a file and writing data to it.

Chapter 77: File I/O

Java 7 NIO (java.nio.file.Path) offers enhanced file system capabilities and replaces java.io.File in certain contexts.
Java provides methods for reading images stored in files.
FileInputStream and FileOutputStream are used for reading and writing raw bytes to files.
Data can be read into a byte array to process it in memory.
Channels provide a more efficient way to copy files by directly accessing underlying resources.
Stream and Writer/Reader APIs are used for working with data streams but with different levels of abstraction.
Scanner class assists in reading data from files using different delimiters and data types.
InputStream and OutputStream can be used when copying files from one location to another.
Binary files can be read using techniques that handle byte-level data.
Channels and Buffers provide efficient means for reading and writing data in blocks.
Directories can be added to the file system programmatically.
Standard output and error can be either blocked or redirected for specific purposes.
An entire file can be read into memory all at once in some cases, depending on the file size and memory availability.
Locking mechanisms prevent simultaneous modifications to files by multiple processes.
BufferedInputStream improves file reading performance by buffering data in memory.
Java provides methods for iterating over directories and printing subdirectories.
Channels and Buffers are used to efficiently write data to files in blocks.
PrintStream provides a convenient way to write data to files in a formatted manner.
Iterating over a directory and filtering files based on specific extensions is commonly used.
ZIP files can be accessed programmatically for reading their contents.

Chapter 78: Scanner

Scanner provides a versatile way to read input data from various sources, including the command line and files.
It uses regular expressions to define how data is parsed and extracted.
Scanner allows using custom delimiters for defining how data is separated into tokens.
System input can be read using a Scanner object.
File input can be read using a Scanner object that reads from a specific file.
The full input stream as a string can be read using Scanner.
Careful closure of Scanner objects is important to release resources.
Integers can be read from the command line using Scanner.

Chapter 79: Interfaces

Multiple interfaces can be implemented by a single class using the implements keyword.
Interfaces declare a set of methods and constants that implementing classes must provide.
Interfaces can extend other interfaces to inherit their methods and constants.
Interfaces are crucial for promoting code reusability, polymorphism, and decoupling.
Java 8 introduced default methods in interfaces allowing specific functionality.
Interfaces can contain modifiers like public, abstract, and static to control method access and behavior.
Generics can work with interfaces to provide flexible and type-safe implementations.
Interfaces can strengthen bounded type parameters by imposing additional constraints on types.
Interfaces can be implemented within abstract classes, allowing abstract classes to inherit interface methods.

Chapter 80: Regular Expressions

Regular expressions (regex) provide powerful patterns for searching and manipulating text.
Capture groups within regex allow extracting specific parts of matched strings.
Flags can be used when compiling a regex pattern to modify its behavior.
Escape characters are used to represent special characters in regex expressions.
Regex can be used to test if a string does not match a given pattern.
Regex literals are a convenient notation for expressing regex patterns directly within code.
Matching a backslash requires special handling due to its use in both strings and regex expressions.

Chapter 81: Comparable and Comparator

Comparable interface allows objects to be compared using their natural ordering.
Comparator interface allows objects to be compared using a custom ordering rule.
Lists can be sorted using either Comparable or Comparator based on the desired ordering.
compareTo and compare methods are responsible for comparing objects and determining their relative order.
Natural sorting is based on the Comparable interface, while explicit sorting requires a Comparator.
The comparing method provides a convenient way to create a Comparator using a lambda function.
Map entries can be sorted based on various criteria using a Comparator.

Chapter 82: Java Floating Point Operations

Comparing floating-point numbers requires using the equals method or tolerance for imprecision.
Overflow and underflow can occur when floating-point values exceed their representable range.
Formatting floating-point values allows controlling their display precision and format.
Java's floating-point operations adhere to the IEEE 754 specification which establishes standard rules.

Chapter 83: Currency and Money

Java provides support for working with currencies using the Currency class.
Custom currencies can be defined and managed using Currency.

Chapter 84: Object Cloning

Deep copy creates an independent copy of an object, including its nested objects.
Copy factory is a dedicated class that creates copies of objects.
Copy constructors create copies of objects during initialization.
Cloning can be achieved by implementing the Cloneable interface.
Shallow copy creates a copy that shares references to the same nested objects.

Chapter 85: Recursion

Recursion involves a function calling itself to solve a problem by breaking it down into smaller, similar subproblems.
Deep recursion can lead to stack overflow due to excessively deep call stacks.
Different types of recursion include linear, binary, and tail recursion.
Fibonacci series is a classic example demonstrated using recursion.
When facing stack overflow, recursion can often be replaced with iterative solutions.
Recursion can be used to perform calculations like finding the nth power of a number.
Traversal of tree data structures is commonly implemented using recursion.
Reversing a string can be done using recursive techniques.
Sum of integers from 1 to n can be efficiently calculated using recursion.

Chapter 86: Converting to and from Strings

Converting from a String to other datatypes requires methods like parseInt, parseDouble, etc.
Conversion between Strings and bytes involves using the getBytes() and new String(bytes) methods.
Base64 encoding and decoding convert data into a printable format.
Converting other datatypes to String involves using String's valueOf() method or toString() methods in other classes.
Converting an InputStream to a String is done by reading the stream's contents and converting the bytes to a string.

Chapter 87: Random Number Generation

Java uses pseudo-random number generators to produce sequences that appear random.
Random numbers within a specific range can be generated using the Random object.
Cryptographically secure pseudo-random numbers are suitable for applications requiring higher security.
Generating random numbers with a specified seed allows producing repeatable sequences.
Selecting random numbers without duplicates is useful in certain scenarios.
Apache Commons Lang3 library provides additional random number generation utilities.

Chapter 88: Singletons

Singletons are classes that ensure only one instance of themselves is created.
Enum singleton provides a simple and thread-safe way to implement a singleton pattern.
Eager initialization creates the singleton instance immediately on class loading.
Thread-safe lazy initialization using a holder class ensures the singleton is created only when needed.
Double-checked locking aims to provide thread-safe lazy initialization, but it might have issues in some cases.
Extending a singleton pattern can pose challenges due to the single instance constraint.

Chapter 89: Autoboxing

Autoboxing refers to the automatic conversion from primitive types to their corresponding wrapper classes.
int and Integer can be used interchangeably due to autoboxing/unboxing, but it comes at the cost of performance.
Auto-unboxing can lead to NullPointerException if an unboxed value is null.
Boolean in if statements automatically unboxes its value.
When working with collections or methods accepting objects, using the wrapper classes is necessary.
There are overhead costs associated with autoboxing due to object creation and type conversions.

Chapter 90: 2D Graphics in Java

The Graphics2D class in Java provides methods for drawing shapes, lines, text, and managing colors.
Examples illustrate how to draw and fill rectangles and ovals.

Chapter 91: JAXB

JAXB (Java Architecture for XML Binding) is a framework for mapping Java objects to XML documents and vice versa.
Unmarshalling reads an XML file and creates corresponding Java objects.
Marshalling takes Java objects and generates XML representations.
Manual field/property mapping provides precise control over XML serialization and deserialization.
XML namespaces can be bound to specific Java classes for serialization and deserialization.
XmlAdapter transforms data during serialization and deserialization.
XmlAdapter can be used to customize the XML format, for example, trimming strings.
Automatic field/property mapping simplifies the process using annotations like @XmlAccessorType.
XmlAdapter instances can be reused to handle existing data structures.

Chapter 92: Class - Java Reflection

Java Reflection is a powerful mechanism for inspecting and manipulating code at runtime.
The getClass() method of the Object class returns the class of an object.

Chapter 93: Networking

Various types of networking protocols exist, each offering different communication methods.

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