Using the batch compiler

Finding the batch compiler

The batch compiler class is located in the JDT Core plug-in. The name of the class is org.eclipse.jdt.compiler.batch.BatchCompiler. It is packaged into plugins/org.eclipse.jdt.core_<version>.jar. Since 3.2, it is also available as a separate download. The name of the file is ecj.jar. Its corresponding source is also available. To get them, go to the download page and search for the section JDT Core Batch Compiler. This jar contains the batch compiler and the javac ant adapter.

Since 3.3, this jar also contains the support for jsr199 (Compiler API) and the support for jsr269 (Annotation processing). In order to use the annotations processing support, a 1.6 VM is required.

So it can be used as a standalone application and inside an Ant build outside of Eclipse.

Running the batch compiler

Which options are available?

The recommended options have an orange background.

When some options are being set multiple times, the batch compiler consumes them from left to right. When the warning option (-warn:....) is used without '+' or '-', this overrides the set of warnings previously specified. So you should make sure that such an option is given before any other usage of the -warn option.

Same applies for the -err: option.

Name Usage
Classpath options
-bootclasspath <dir 1>;<dir 2>;...;<dir P> This is a list of directories or jar files used to bootstrap the class files used by the compiler. By default the libraries of the running VM are used. Entries are separated by the platform path separator.
Each directory or file can specify access rules for types between '[' and ']'.

If no bootclasspath is specified, the compiler will infer it using the following system properties sun.boot.class.path, vm.boot.class.path or org.apache.harmony.boot.class.path in this order respectively.

-classpath <dir 1>;<dir 2>;...;<dir P>
This is a list of directories or jar files used to compile the source files. The default value is the value of the property "java.class.path". Entries are separated by the platform path separator.
Each directory or file can specify access rules for types between '[' and ']' (e.g. [-X] to forbid access to type X, [~X] to discourage access to type X, [+p/X:-p/*] to forbid access to all types in package p but allow access to p/X).
The compiler follows the Class-Path clauses of jar files' manifests recursively and appends each referenced jar file to the end of the classpath, provided it is not on the classpath yet.
-extdirs <dir 1>;<dir 2>;...;<dir P> This is a list of directories used to specify the location of extension zip/jar files. Entries are separated by the platform path separator.
-endorseddirs <dir 1>;<dir 2>;...;<dir P> This is a list of directories used to specify the location of endorsed zip/jar files. Entries are separated by the platform path separator.
-sourcepath <dir 1>;<dir 2>;...;<dir P> This is a list of directories used to specify the source files. Entries are separated by the platform path separator.
Each directory can specify access rules for types between '[' and ']'.
-d <dir 1>|none This is used to specify in which directory the generated .class files should be dumped. If it is omitted, no package directory structure is created.
If you want to generate no .class file at all, use -d none.
-encoding <encoding name> Specify default encoding for all source files. Custom encoding can also be specified on a per file basis by suffixing each input source file/folder name with [<encoding name>]. For example[utf8] would specify the UTF-8 encoding for the compilation unit located in the current user directory.

If multiple default source file encodings are specified, the last one will be used.

For example:

  • ... -encoding UTF-8[Cp1252][UTF-16] ....
    All source files will be read using UTF-8 encoding (this includes will be read using Cp1252 encoding and will be read using UTF-16 encoding.
  • ... -encoding UTF-8 -encoding UTF-16 ....
    All source files will be read using UTF-16 encoding. The -encoding option for UTF-8 is ignored.
  • ... -encoding Cp1252 /foo/bar/[UTF-16] /foo/bar[UTF-8] ....
    All source files will be read using Cp1252 encoding. is the only file inside the /foo/bar directory to be read using the encoding UTF-16. All other files in that directory will use UTF-8 encoding.
Compliance options
-target 1.1 to 1.7 or (5, 5.0, etc) This specifies the .class file target setting. The possible value are:
  • 1.1 (major version: 45 minor: 3)
  • 1.2 (major version: 46 minor: 0)
  • 1.3 (major version: 47 minor: 0)
  • 1.4 (major version: 48 minor: 0)
  • 1.5, 5 or 5.0 (major version: 49 minor: 0)
  • 1.6, 6 or 6.0 (major version: 50 minor: 0)
  • 1.7, 7 or 7.0 (major version: 51 minor: 0)
Defaults are:
  • 1.1 in -1.3 mode
  • 1.2 in -1.4 mode
  • 1.5 in -1.5 mode
  • 1.6 in -1.6 mode
  • 1.7 in -1.7 mode

clcd1.1 can be used to generate the StackMap attribute.

-1.3 Set compliance level to 1.3. Implicit -source 1.3 -target 1.1.
-1.4 Set compliance level to 1.4 (default). Implicit -source 1.3 -target 1.2.
-1.5 Set compliance level to 1.5. Implicit -source 1.5 -target 1.5.
-1.6 Set compliance level to 1.6. Implicit -source 1.6 -target 1.6.
-1.7 Set compliance level to 1.7. Implicit -source 1.7 -target 1.7.
-source 1.1 to 1.7 or (5, 5.0, etc) This is used to specify the source level expected by the compiler.
The possible value are:
  • 1.3
  • 1.4
  • 1.5, 5 or 5.0
  • 1.6, 6 or 6.0
  • 1.7, 7 or 7.0
Defaults are:
  • 1.3 in -1.3 mode
  • 1.3 in -1.4 mode
  • 1.5 in -1.5 mode
  • 1.6 in -1.6 mode
  • 1.7 in -1.7 mode
In 1.4, assert is treated as a keyword. In 1.5 and 1.6, enum and assert are treated as a keywords.
Warning options
-?:warn -help:warn Display advanced warning options
-warn:... Specify the set of enabled warnings.
-warn:none disable all warnings
-warn:<warning tokens separated by ,> enable exactly the listed warnings
-warn:+<warning tokens separated by ,> enable additional warnings
-warn:-<warning tokens separated by ,> disable specific warnings


  • -warn:unusedLocal,deprecation enables only the given two warning options and disables all the other options
  • -warn:-unusedLocal,deprecation,+fallthrough disables unusedLocal and deprecation, enables fallthrough, and leaves the other warning options untouched
In the column Default below, a mark "+/-" indicates that an option covers several fine grained warning variants, some of which are enabled by default, others disabled. This means that specifying the given option with "+" will enable more warnings than the default, and specifying "-" disables some that are enabled by default.
Default Token name Description
+/- allDeadCode dead code including trivial if (DEBUG) check
+/- allDeprecation deprecation even inside deprecated code
- allJavadoc invalid or missing Javadoc
- allOver-ann all missing @Override annotations (superclass and superinterfaces)
- all-static-method all method can be declared as static warnings
+ assertIdentifier occurrence of assert used as identifier
- boxing autoboxing conversion
+ charConcat when a char array is used in a string concatenation without being converted explicitly to a string
+ compareIdentical comparing identical expressions
- conditionAssign possible accidental boolean assignment
+ constructorName method with constructor name
+ deadCode dead code excluding trivial if (DEBUG) check
- dep-ann missing @Deprecated annotation
+/- deprecation usage of deprecated type or member outside deprecated code
+ discouraged use of types matching a discouraged access rule
- emptyBlock undocumented empty block
+ enumIdentifier occurrence of enum used as identifier
+ enumSwitch incomplete enum switch
- enumSwitchPedantic report missing enum switch cases even in the presence of a default case
- fallthrough possible fall-through case
- fieldHiding field hiding another variable
+ finalBound type parameter with final bound
+ finally finally block not completing normally
+ forbidden use of types matching a forbidden access rule
- hashCode missing hashCode() method when overriding equals()
+/- hiding macro for fieldHiding, localHiding, maskedCatchBlock, and typeHiding
- includeAssertNull raise null warnings for variables that got tainted in an assert expression
- indirectStatic indirect reference to static member
- inheritNullAnnot consider null annotations as being inherited from an overridden method to any overriding methods
+ intfAnnotation annotation type used as super interface
+ intfNonInherited interface non-inherited method compatibility
- intfRedundant find redundant superinterfaces
- invalidJavadoc macro to toggle the 'malformed Javadoc comments' option and all its sub-options listed below
- invalidJavadocTag report invalid Javadoc tags in Javadoc comments.
- invalidJavadocTagDep report invalid deprecated references in Javadoc tag arguments
- invalidJavadocTagNotVisible report invalid non-visible references in Javadoc tag arguments
- invalidJavadocVisibility(<visibility>) specify visibility modifier ("public", "protected" or "private") for malformed Javadoc tag warnings. Usage example: invalidJavadocVisibility(public)
- javadoc invalid Javadoc
- localHiding local variable hiding another variable
+ maskedCatchBlock hidden catch block
- missingJavadocTags macro to toggle the 'missing Javadoc tags' option and all its sub-options listed below
- missingJavadocTagsMethod report missing Javadoc tags for a method's type parameters
- missingJavadocTagsOverriding report missing Javadoc tags in overriding methods
- missingJavadocTagsVisibility(<visibility>) specify visibility modifier ("public", "protected" or "private") for missing Javadoc tags warnings. Usage example: missingJavadocTagsVisibility(public)
- missingJavadocComments macro to toggle the 'missing Javadoc comments' option and all its sub-options listed below
- missingJavadocCommentsOverriding report missing Javadoc comments in overriding methods
- missingJavadocCommentsVisibility(<visibility>) specify visibility modifier ("public", "protected" or "private") for missing Javadoc comments warnings. Usage example: missingJavadocCommentsVisibility(public)
- nls non-nls string literals (lacking of tags //$NON-NLS-<n>)
+ noEffectAssign assignment with no effect
+ nonnullNotRepeated nonnull parameter annotation from overridden method is not repeated in an overriding method. Is effective only with the nullAnnot option enabled.
+/- null potential missing or redundant null check
- nullAnnot enable annotation based null analysis.
If desired, the annotation types to be interpreted by the compiler can be specified by appending (nullable|nonnull|nonnullbydefault), where each annotation type is specified using its fully qualified name.
Usage example: nullAnnot(p.Nullable|p.NonNull|p.NonNullByDefault)
Enabling this option enables all null-annotation related sub-options. These can be individually controlled using options listed below
- nullAnnotConflict report conflicts between null annotation specified and nullness inferred. Is effective only with the nullAnnot option enabled.
- nullAnnotRedundant report redundant specification of null annotation. Is effective only with the nullAnnot option enabled.
- nullDereference missing null check
- nullUncheckedConversion report unchecked conversion from unannotated type to @NonNull type. Is effective only with the nullAnnot option enabled.
- over-ann missing @Override annotation (superclass only)
- paramAssign assignment to a parameter
+ pkgDefaultMethod attempt to override package-default method
+ raw usage a of raw type (instead of a parameterized type)
+/- resource (potentially) unsafe usage of resource of type Closeable
- semicolon unnecessary semicolon or empty statement
+ serial missing serialVersionUID
- specialParamHiding constructor or setter parameter hiding another field
+/- static-access macro for indirectStatic and staticReceiver
- static-method an instance method that could be as a static method
+ staticReceiver if a non static receiver is used to get a static field or call a static method
- super overriding a method without making a super invocation
+ suppress enable @SuppressWarnings
- switchDefault switch statement lacking a default case
- syncOverride missing synchronized in synchronized method override
- syntheticAccess when performing synthetic access for innerclass
- tasks enable support for tasks tags in source code
+ typeHiding type parameter hiding another type
+ unavoidableGenericProblems report even unavoidable type safety problems due to raw APIs
+ unchecked unchecked type operation
- unnecessaryElse unnecessary else clause
- unqualifiedField unqualified reference to field
+/- unused macro for unusedImport, unusedLabel, unusedLocal, unusedPrivate, unusedThrown, unusedTypeArgs, and unusedTypeParameter
- unusedAllocation allocating an object that is not used
- unusedArgument unused method parameter (deprecated option; use unusedParam instead)
+ unusedImport unused import reference
+ unusedLabel unused label
+ unusedLocal unused local variable
+ unusedParam unused method parameter
+ unusedParamImplementing unused parameter for implementing method
+ unusedParamIncludeDoc unused parameter documented in a Javadoc comment tag
+ unusedParamOverriding unused parameter for overriding method
+ unusedPrivate unused private member declaration
- unusedThrown unused declared thrown exception
- unusedThrownIncludeDocComment unused declared thrown exception documented in a Javadoc comment tag
- unusedThrownExemptExceptionThrowable report unused declared thrown exception but exempt Exception and Throwable
- unusedThrownWhenOverriding unused declared thrown exception in overriding method
+ unusedTypeArgs unused type arguments for method and constructor
+ unusedTypeParameter unused type parameter
- uselessTypeCheck unnecessary cast/instanceof operation
+ varargsCast varargs argument need explicit cast
+/- warningToken unhandled or unused warning token in @SuppressWarnings
-nowarn No warning (equivalent to -warn:none)
-err:... Specify the set of enabled warnings that are converted to errors.
e.g. -err:unusedLocal,deprecation
unusedLocal and deprecation warnings will be converted to errors. All other warnings are still reported as warnings.
-err:<warning tokens separated by ,> convert exactly the listed warnings to errors
-err:+<warning tokens separated by ,> convert additional warnings to errors
-err:-<warning tokens separated by ,> remove specific warnings from being converted to errors
-deprecation Equivalent to -warn:+deprecation.
-properties <file> Set warnings/errors option based on the properties file contents. This option can be used with -nowarn, -err:.. or -warn:.. options, but the last one on the command line sets the options to be used.

The properties file contents can be generated by setting project specific settings on an existing java project and using the file in .settings/org.eclipse.jdt.core.prefs file as a properties file, or a simple text file that is defined entry/value pairs using the constants defined in the org.eclipse.jdt.core.JavaCore class. Of those constants declared in this class, all options starting with "org.eclipse.jdt.core.compiler." are interpreted by the batch compiler.


To ensure that a property file has the same effect when used in the IDE and for the batch compiler, use of the -properties option will change the defaults for a few options:

-gdefault changed to all enabled
-preserveAllLocalsdefault changed to enabled
-enableJavadocdefault changed to enabled
error/warning forbiddendefault changed to error
Debug options
-g[:none|:lines,vars,source] Set the debug attributes level
-g All debug info (equivalent to -g:lines,vars,source)
-g:none No debug info
-g:[lines,vars,source] Selective debug info
Not specifying this option is equivalent to setting -g:lines,source.
-preserveAllLocals Explicitly request the compiler to preserve all local variables (for debug purpose). If omitted, the compiler will remove unused locals.
-parameters Explicitly request the compiler to preserve information about the formal parameters of a method (such as their names) to be accessed from reflection libraries, annotation processing, code weaving, and in the debugger. This option is supported from target level 1.8 and later.
Annotation processing options (require a 1.6 VM or above and are used only if the compliance is 1.6)
-Akey[=value] Annotation processors options that are passed to annotation processors. key is made of identifiers separated by dots
-proc:[only|none] If -proc:only is specified, the annotation processors will run but no compilation will be performed. If -proc:none is specified, annotation processors will not be discovered or run; compilation will proceed as if no annotation processors were found. By default the compiler must search the classpath for annotation processors, so specifying -proc:none may speed compilation if annotation processing is not required.
-processor <class1[,class2,...]> Qualified class names of annotation processors to run. If specified, the normal processor discovery process will be skipped.
-processorpath <dir 1>;<dir 2>;...;<dir P> A list of directories or jar files which will be searched for annotation processors. Entries are separated by the platform path separator. If not specified, the classpath will be searched instead.
-s <dir> The directory where generated source files will be created.
-XprintProcessorInfo Print information about which annotations and which elements a processor is asked to process
-XprintRounds Print information about annotation processing rounds
-classNames <class1[,class2,...]> Qualified names of binary types that need to be processed
Ignored options (for compatibility with javac options)
-J<option> Pass option to the virtual machine
-X<option> Specify non-standard option. -Xemacs is not ignored.
-X Print non-standard options and exit
-O Optimize for execution time
Advanced options
@<file> Read command-line arguments from file
-maxProblems <n> Max number of problems per compilation unit (100 by default)
-log <filename> Specify a log file in which all output from the compiler will be dumped. This is really useful if you want to debug the batch compiler or get a file which contains all errors and warnings from a batch build. If the extension is .xml, the generated log will be an xml file.
-Xemacs Use emacs style to present errors and warnings locations into the console and regular text logs. XML logs are unaffected by this option. With this option active, the message:
2. WARNING in /workspace/
(at line 8)...

is presented as:
/workspace/ warning: The method...
-proceedOnError[:Fatal] Keep compiling in spite of errors, dumping class files with problem methods or problem types. This is recommended only if you want to be able to run your application even if you have remaining errors.
With ":Fatal", all optional errors are treated as fatal and this leads to code that will abort if an error is reached at runtime. Without ":Fatal", optional errors don't prevent the proper code generation and the produced .class files can be run without a problem.
-verbose Print accessed/processed compilation units in the console or the log file if specified.
-referenceInfo Compute reference info. This is useful only if connected to the builder. The reference infos are useless otherwise.
-progress Show progress (only in -log mode).
-time Display speed information.
-noExit Do not call System.exit(n) at end of compilation (n=0 if no error).
-repeat <n> Repeat compilation process <n> times (perf analysis).
-inlineJSR Inline JSR bytecode (implicit if target >= 1.5).
-enableJavadoc Consider references inside Javadoc. The Javadoc options are effective only when this option is enabled.
-missingNullDefault When annotation based null analysis is enabled (using "nullAnnot", above), this option will raise a warning whenever there is no default annotation on a package or a type.
Helping options
-? -help Display the help message.
-v -version Display the build number of the compiler. This is very useful to report a bug.
-showversion Display the build number of the compiler and continue. This is very useful to report a bug.


d:\temp -classpath rt.jar -time -g -d d:/tmp It compiles all source files in d:\temp and its subfolders. The classpath is simply rt.jar. It generates all debug attributes and all generated .class files are dumped in d:\tmp. The speed of the compiler will be displayed once the batch process is completed.
d:\temp\ -classpath d:\temp;rt.jar -g:none It compiles only and its dependant files if any, retrieving dependant files from d:\temp. The classpath is d:\temp followed by rt.jar, which means that all necessary classes are searched first in d:\temp and then in rt.jar. It generates no debug attributes and all generated .class files are dumped in d:\temp.