Java basic namespaces and related things (Java engineers must, or kill heaven)

Java.lang (provides a basic class for programming using the Java programming language)
Java.lang.annotation (provides a reference object class that supports some degree of interaction with the garbage collector)
Java.lang.instrument (provides services that allow the Java programming language Agent to detect programs running on the JVM)
Java.lang.management (provides a management interface for monitoring and managing Java virtual machines and the operating system on which the Java Virtual machine runs)
Java.lang.ref (provides a reference object class that supports some degree of interaction with the garbage collector)
Java.lang.reflect (provides classes and interfaces to obtain reflection information about classes and objects.) ）

java.io (provides system input and output via data flow, serialization, and file system)
Java.math (provides classes for performing arbitrary-precision integer Arithmetic (BigInteger) and arbitrary-precision fractional arithmetic (BigDecimal))
java.net (provides classes for implementing network applications)
Java.nio (defines a buffer as a data container and provides an overview of other NIO packages)
Java.nio.channels (defines the various channels that represent connections to entities (such as files and sockets) that can perform I/O operations; Defines selectors for multiplexing, non-blocking I/O operations)
Java.nio.charset (defines the charset, decoders, and encoders that are used to convert between byte and Unicode characters)

Java.security (provides classes and interfaces for the security framework)
Java.security.cert
Java.security.interfaces
Java.security.spec

java.sql (provides an API to access and process data stored in a data source (typically a relational database) using the JAVATM programming language)
Java.text (provides classes and interfaces that handle text, dates, numbers, and messages in a way unrelated to natural language)
Java.text.spi

Java.util (includes collection framework, Legacy Collection class, event model, date and time facility, internationalization, and various utility classes)
Java.util.concurrent (utility classes that are common in concurrent programming)
Java.util.concurrent.atomic (small toolkit for classes that supports thread-safe programming for unlocking on a single variable)
Java.util.concurrent.locks (Interfaces and classes that provide a framework for lock and wait conditions, unlike built-in synchronizations and monitors)
Java.util.jar (a class that provides a read-write jar (Java ARchive) file format based on a standard ZIP file format with an optional manifest file. ）
Java.util.logging (provides classes and interfaces for the JAVATM 2 platform core Logging tool. ）
Java.util.prefs (This package allows applications to store and obtain user and system preferences and configuration data)
Java.util.regex (class to match the character sequence with the regular expression specified pattern)
JAVA.UTIL.SPI (Service provider class in Java.util package)
Java.util.zip (provides classes for reading and writing standard zip and GZIP file formats)

Java.beans
Java.beans.beancontext

Yjfx:java NiO, Netty, Tcp/http and other protocols

Memory model, garbage collection, class loading
Multithreading, High concurrency
Lock type, optimistic lock/cas, lightweight/biased lock
IO model, NIO principle
Various frameworks, architecture design (Dobbox, spring)

Java basic namespaces and related things (Java engineers must, or kill heaven)