Common Java Libraries |

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Java provides a rich set of libraries. Below are some of the most commonly used classes.

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1. Core Java Libraries

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The Java Standard Library provides a rich set of built-in libraries. Here are some commonly used core libraries:

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Category	Library Name	Main Function
Collection Framework	java.util.ArrayList	Dynamic array implementation
	java.util.LinkedList	Doubly linked list implementation
	java.util.HashMap	Map implemented with a hash table
	java.util.Vector	Implements a dynamic array
	java.util.HashSet	Set based on a hash table
	java.util.Scanner	Captures user input
	java.util.regex.Pattern	Regular expressions
	java.util.regex.Macher	Regular expressions
IO/NIO	java.io.File	File and directory operations
	java.nio.file.Files	Utility class for file operations
	java.io.InputStream	Base class for byte streams
	java.io.OutputStream	Base class for byte streams
Multithreading	java.lang.Thread	Thread operation class
	java.util.concurrent.ExecutorService	Thread pool management
Date & Time	java.time.LocalDate	Date handling
	java.time.LocalDateTime	Date and time handling
	java.time.ZonedDateTime	Date and time with timezone
	java.util.Date	Current date
	java.text.SimpleDateFormat	Date/time formatting
	java.util.Calendar	Handles date and time
	java.util.GregorianCalendar	Implements the Gregorian calendar
	java.time.Instant	Represents an instantaneous point on the timeline
	java.time.ChronoUnit	Standard units for measuring time
	java.time.Period	Represents a time interval between two dates
	java.time.Duration	Represents a time-based duration (hours, minutes, seconds, nanoseconds)
Network Programming	java.net.URL	URL handling
	java.net.Socket	Socket programming

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2. Common Third-Party Libraries

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Here are widely used third-party libraries in the Java ecosystem:

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Category	Library Name	Main Function	Official Website
JSON Processing	Jackson	JSON serialization/deserialization	https://github.com/FasterXML/jackson
	Gson	Google's JSON library	https://github.com/google/gson
Unit Testing	JUnit	Java unit testing framework	https://junit.org/junit5/
	Mockito	Mock testing framework	https://site.mockito.org/
Logging	Log4j	Logging framework	https://logging.apache.org/log4j/
	SLF4J	Logging facade framework	https://www.slf4j.org/
Web Development	Spring Framework	Enterprise application framework	https://spring.io/projects/spring-framework
	Spring Boot	Rapid application development framework	https://spring.io/projects/spring-boot
Database	Hibernate	ORM framework	https://hibernate.org/
	MyBatis	SQL mapping framework	https://mybatis.org/mybatis-3/
Build Tools	Maven	Project build and dependency management	https://maven.apache.org/
	Gradle	Flexible build tool	https://gradle.org/

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3. How to Choose the Right Library

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3.1 Evaluation Criteria

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1. Functional Requirements: First, clarify what features the project needs
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2. Community Support: An active community means better support and documentation
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3. Performance: Requires special consideration for performance-sensitive applications
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4. Learning Curve: Consider the team's learning cost
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5. Maintenance Status: Check if the project is still actively maintained
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3.2 Version Selection Recommendations

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• Prioritize LTS (Long-Term Support) versions
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• Avoid using versions that have reached end-of-life
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• New projects can consider newer stable versions
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4. Usage Examples

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4.1 Processing JSON with Jackson

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Example

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import com.fasterxml.jackson.databind.ObjectMapper;\n\npublic class JsonExample {\n\npublic static void main(String[] args){\n\n ObjectMapper mapper =new ObjectMapper();\n\ntry{\n\n// Object to JSON\n\nString json = mapper.writeValueAsString(new User("Zhang San", 25));\n\nSystem.out.println(json);\n\n// JSON To Object\n\n User user = mapper.readValue(json, User.class);\n\nSystem.out.println(user);\n\n}catch(Exception e){\n\n e.printStackTrace();\n\n}\n\n}\n\n}

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4.2 Unit Testing with JUnit

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Example

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import org.junit.jupiter.api.Test;\n\nimport static org.junit.jupiter.api.Assertions.*;\n\nclass CalculatorTest {\n\n @Test\n\nvoid testAdd(){\n\n Calculator calc =new Calculator();\n\n assertEquals(5, calc.add(2, 3));\n\n}\n\n}