# Module jdk.compiler

module jdk.compiler
Defines the implementation of the system Java compiler and its command line equivalent, javac.

The `com.sun.source.*` packages provide the Compiler Tree API: an API for accessing the abstract trees (ASTs) representing Java source code and documentation comments, used by javac, javadoc and related tools.

## javac

This module provides the equivalent of command-line access to javac via the `ToolProvider` and `Tool` service provider interfaces (SPIs), and more flexible access via the `JavaCompiler` SPI.

Instances of the tools can be obtained by calling `ToolProvider.findFirst` or the service loader with the name `"javac"`.

In addition, instances of `JavaCompiler.CompilationTask` obtained from JavaCompiler can be downcast to `JavacTask` for access to lower level aspects of javac, such as the `Abstract Syntax Tree` (AST).

This module uses the `FileSystemProvider` API to locate file system providers. In particular, this means that a jar file system provider, such as that in the `jdk.zipfs` module, must be available if the compiler is to be able to read JAR files.

### Options and Environment Variables

The full set of options and environment variables supported by javac is given in the javac Tool Guide. However, there are some restrictions when the compiler is invoked through its API.

- The `-J` option is not supported. Any necessary VM options must be set in the VM used to invoke the API. `IllegalArgumentException` will be thrown if the option is used when invoking the tool through the `JavaCompiler` API; an error will be reported if the option is used when invoking javac through the `ToolProvider` or legacy `Main` API.

- The "classpath wildcard" feature is not supported. The feature is only supported by the native launcher. When invoking the tool through its API, all necessary jar files should be included directly in the `--class-path` option, or the `CLASSPATH` environment variable. When invoking the tool through its API, all components of the class path will be taken literally, and will be ignored if there is no matching directory or file. The `-Xlint:paths` option can be used to generate warnings about missing components.

The following restrictions apply when invoking the compiler through the `JavaCompiler` interface.

- Argument files (so-called @-files) are not supported. The content of any such files should be included directly in the list of options provided when invoking the tool though this API. `IllegalArgumentException` will be thrown if the option is used when invoking the tool through this API.

- The environment variable `JDK_JAVAC_OPTIONS` is not supported. Any options defined in the environment variable should be included directly in the list of options provided when invoking the API; any values in the environment variable will be ignored.

- Options that are just used to obtain information (such as `--help`, `--help-extended`, `--version` and `--full-version`) are not supported. `IllegalArgumentException` will be thrown if any of these options are used when invoking the tool through this API.

- Path-related options depend on the file manager being used when calling `JavaCompiler.getTask(Writer, JavaFileManager, DiagnosticListener, Iterable, Iterable, Iterable)`. The "standard" options, such as `--class-path`, `--module-path`, and so on are available when using the default file manager, or one derived from it. These options may not be available and different options may be available, when using a different file manager. `IllegalArgumentException` will be thrown if any option that is unknown to the tool or the file manager is used when invoking the tool through this API.

Note that the `CLASSPATH` environment variable is honored when invoking the compiler through its API, although such use is discouraged. An environment variable cannot be unset once a VM has been started, and so it is recommended to ensure that the environment variable is not set when starting a VM that will be used to invoke the compiler. However, if a value has been set, any such value can be overridden by using the `--class-path` option when invoking the compiler, or setting `StandardLocation.CLASS_PATH` in the file manager when invoking the compiler through the `JavaCompiler` interface.

### SuppressWarnings

JLS 9.6.4.5 specifies a number of strings that can be used to suppress warnings that may be generated by a Java compiler. In addition, javac also supports other strings that can be used to suppress other kinds of warnings. The following table lists all the strings that can be used with `@SuppressWarnings`.

Strings supported by `SuppressWarnings`
String | Suppress Warnings About ...
--- | ---
`auxiliaryclass` | an auxiliary class that is hidden in a source file, and is used from other files
`cast` | use of unnecessary casts
`classfile` | issues related to classfile contents
`dangling-doc-comments` | issues related to "dangling" documentation comments, not attached to a declaration
`deprecation` | use of deprecated items
`dep-ann` | items marked as deprecated in a documentation comment but not using the `@Deprecated` annotation
`divzero` | division by constant integer `0`
`empty` | empty statement after `if`
`exports` | issues regarding module exports
`fallthrough` | falling through from one case of a `switch` statement to the next
`finally` | `finally` clauses that do not terminate normally
`identity` | use of a value-based class where an identity class is expected
`incubating` | use of incubating modules
`lossy-conversions` | possible lossy conversions in compound assignment
`missing-explicit-ctor` | missing explicit constructors in public and protected classes in exported packages
`module` | module system related issues
`opens` | issues regarding module opens
`overloads` | issues regarding method overloads
`overrides` | issues regarding method overrides
`path` | invalid path elements on the command line
`preview` | use of preview language features
`rawtypes` | use of raw types
`removal` | use of API that has been marked for removal
`restricted` | use of restricted methods
`requires-automatic` | use of automatic modules in the `requires` clauses
`requires-transitive-automatic` | automatic modules in `requires transitive`
`serial` | `Serializable` classes that do not have a `serialVersionUID` field, or other suspect declarations in `Serializable` and `Externalizable` classes and interfaces
`static` | accessing a static member using an instance
`strictfp` | unnecessary use of the `strictfp` modifier
`synchronization` | synchronization attempts on instances of value-based classes; this key is a deprecated alias for `identity`, which has the same uses and effects. Users are encouraged to use the `identity` category for all future and existing uses of `synchronization`
`text-blocks` | inconsistent white space characters in text block indentation
`this-escape` | superclass constructor leaking `this` before subclass initialized
`try` | issues relating to use of `try` blocks (that is, try-with-resources)
`unchecked` | unchecked operations
`varargs` | potentially unsafe vararg methods
`doclint:accessibility` | accessibility issues found in documentation comments
`doclint:all` | all issues found in documentation comments
`doclint:html` | HTML issues found in documentation comments
`doclint:missing` | missing items in documentation comments
`doclint:reference` | reference issues found in documentation comments
`doclint:syntax` | syntax issues found in documentation comments

Tool Guides:
  javac
Since:
  9

- ## Packages

  Exports
  Package
  Description
  com.sun.source.doctree
  Provides interfaces to represent documentation comments as abstract syntax trees (AST).
  com.sun.source.tree
  Provides interfaces to represent source code as abstract syntax trees (AST).
  com.sun.source.util
  Provides utilities for operations on abstract syntax trees (AST).
  com.sun.tools.javac
  This package provides a legacy entry point for the javac tool.
  Indirect Exports
  From
  Packages
  java.compiler
  javax.annotation.processing javax.lang.model javax.lang.model.element javax.lang.model.type javax.lang.model.util javax.tools

- ## Modules

  Requires
  Modifier
  Module
  Description
  transitive
  java.compiler
  Defines the Language Model, Annotation Processing, and Java Compiler APIs.

- ## Services

  Provides
  Type
  Description
  JavaCompiler
  Interface to invoke Java programming language compilers from programs.
  Tool
  Common interface for tools that can be invoked from a program.
  ToolProvider
  Use `ToolProvider.findFirst("javac")` to obtain an instance of a `ToolProvider` that provides the equivalent of command-line access to the `javac` tool.
  Uses
  Type
  Description
  Plugin
  The interface for a javac plug-in.
  Processor
  The interface for an annotation processor.