Getting started with Java Language Inheritance Streams Exceptions and exception handling Collections Lambda Expressions Generics File I/O Arrays Interfaces Maps Strings InputStreams and OutputStreams Default Methods Classes and Objects Basic Control Structures Concurrent Programming (Threads)Console I/O Singletons Visibility (controlling access to members of a class)Regular Expressions Autoboxing Documenting Java Code Executor, ExecutorService and Thread pools Object Class Methods and Constructor JAXB Primitive Data Types Networking Optional Enums HttpURLConnection Annotations Audio Date Class Calendar and its Subclasses Nashorn JavaScript engine Java Native Interface Remote Method Invocation (RMI)Iterator and Iterable Operators Asserting Scanner Properties Class Preferences Reflection API Constructors ByteBuffer Serialization JSON in Java Random Number Generation Recursion Polymorphism StringBuilder Reference Data Types Bit Manipulation Java Agents Encapsulation Type Conversion BigInteger BigDecimal RSA Encryption Varargs (Variable Argument)ThreadLocal Logging (java.util.logging)Using the static keyword Disassembling and Decompiling Resources (on classpath)log4j / log4j2 JVM Flags Oracle Official Code Standard Character encoding Java Memory Management Immutable Objects Object Cloning Alternative Collections Lists BufferedWriter LocalTime Sets Comparable and Comparator JVM Tool Interface Nested and Inner Classes Apache Commons Lang Getters and Setters The Classpath Bytecode Modification XML Parsing using the JAXP APIs Reference Types Localization and Internationalization JAX-WS XML XPath Evaluation Java Performance Tuning Parallel programming with Fork/Join framework Common Java Pitfalls Non-Access Modifiers Java Compiler - 'javac'XJC Process Installing Java (Standard Edition)Command line Argument Processing Dates and Time (java.time.*)Fluent Interface XOM - XML Object Model Just in Time (JIT) compiler FTP (File Transfer Protocol)Java Native Access Modules Java Pitfalls - Exception usage Java Pitfalls - Language syntax ServiceLoader Classloaders Object References Java Pitfalls - Performance Issues Creating Images Programmatically Applets NIO - Networking New File I/O Secure objects Java Pitfalls - Threads and Concurrency Splitting a string into fixed length parts Java Pitfalls - Nulls and NullPointerException SecurityManager JNDI super keyword The java.util.Objects Class The Java Command - 'java' and 'javaw'Atomic Types Java Floating Point Operations Converting to and from Strings sun.misc.Unsafe Java Memory Model Java deployment Java plugin system implementations Queues and Deques Runtime Commands NumberFormat Security & Cryptography Java Virtual Machine (JVM)Unit Testing JavaBean Expressions Literals Java SE 8 Features Java SE 7 Features Packages Currency and Money Concurrent Collections Using ThreadPoolExecutor in MultiThreaded applications.Java Editions, Versions, Releases and Distributions Dynamic Method Dispatch JMX Security & Cryptography Generating Java Code JShell Benchmarks Collection Factory Methods Multi-Release JAR Files Stack-Walking API TreeMap and TreeSet Sockets Java Sockets Using Other Scripting Languages in Java Functional Interfaces List vs SET 2D Graphics in Java Class - Java Reflection Dequeue Interface Enum Map EnumSet class Local Inner Class Java Print Service Immutable Class String Tokenizer FileUpload to AWS AppDynamics and TIBCO BusinessWorks Instrumentation for Easy Integration Readers and Writers Hashtable Enum starting with number SortedMap WeakHashMap LinkedHashMap StringBuffer Choosing Collections C++ Comparison CompletableFuture

Modules

Remarks:

The use of modules is encouraged but not required, this allows existing code to continue working in Java 9. It also allows for a gradual transition to modular code.

Any non-modular code is put in an unnamed module when it is compiled. This is a special module that is able to use types from all other modules but only from packages which have an exports declaration.

All packages in the unnamed module are exported automatically.

Keywords, e.g. module etc..., are restricted in use within the module declaration but can be continue to be used as identifiers elsewhere.

Defining a basic module

Modules are defined in a file named module-info.java, named a module descriptor. It should be placed in the source-code root:

 |-- module-info.java
 |-- com
     |-- example
         |-- foo
             |-- Foo.java
         |-- bar
             |-- Bar.java

Here is a simple module descriptor:

module com.example {
    requires java.httpclient;
    exports com.example.foo;
}

The module name should be unique and it is recommended that you use the same Reverse-DNS naming notation as used by packages to help ensure this.

The module java.base, which contains Java's basic classes, is implicitly visible to any module and does not need to be included.

The requires declaration allows us to use other modules, in the example the module java.httpclient is imported.

A module can also specify which packages it exports and therefore makes it visible to other modules.

The package com.example.foo declared in the exports clause will be visible to other modules. Any sub-packages of com.example.foo will not be exported, they need their own export declarations.

Conversely, com.example.bar which is not listed in exports clauses will not be visible to other modules.

Syntax:

requires java.xml;
requires public java.xml; # exposes module to dependents for use
exports com.example.foo; # dependents can use public types in this package
exports com.example.foo.impl to com.example.bar; # restrict usage to a module

Contributors

Topic Id: 5286

Example Ids: 18827

This site is not affiliated with any of the contributors.