Release 4.0.0 of the Checker Framework
Suzanne Millstein
The Checker Framework lets you create and/or run pluggable type checkers, in order to detect and prevent bugs in your code.
You can find documentation and download links at:
https://CheckerFramework.org/
Here are the changes for Checker Framework version 4.0.0:
Version 4.0.0 (2026-04-07)
User-visible changes
To run the Checker Framework, you need to use a JDK 17 or later version of javac. That is, you need to use JDK 17 or later when compiling your code.
The Checker Framework can type-check any Java project, including projects that compile to Java 8 or 11 bytecodes and run on JRE versions 8 or 11. That is, your code can run under any release of Java, from Java 8 onward.
The type qualifiers and utility libraries in checker-qual.jar and checker-util.jar still use Java 11 bytecode. Thus, they may be used in projects that run under Java 11 or later.
Changes since version 3.0.0
Since version 3.0.0, 91 authors have made over 4500 commits and closed over 600 issues. Thanks to everyone who contributed!
New checkers include:
- The Index Checker warns about out-of-bounds accesses to arrays and strings.
- The Initialized Fields Checker warns if a constructor does not initialize a field.
- The Resource Leak Checker guarantees that every resource is closed rather than leaked. Examples of resources are a channel, executor,
ExecutionControl, file,FileLock,Formatter, reader,Scanner, socket, stream, writer, etc. - The SQL Quotes Checker helps prevent SQL injection vulnerabilities.
New command-line arguments include:
-AskipFiles,-AonlyFiles-AassumeSideEffectFree,-AassumeDeterministic,-AassumePure,-AassumePureGetters-AuseConservativeDefaultsForUncheckedCode-AignoreRawTypeArguments-AwarnRedundantAnnotations-Ainfer=ajava,-AinferOutputDirectory,-AinferOutputOriginal,-AshowWpiFailedInferences-AshowSuppressWarningsStrings,-AwarnUnneededSuppressionsExceptions-AshowPrefixInWarningMessages-AstubNoWarnIfNotFound,-AstubWarnNote,-AmergeStubsWithSource-Aonelinemsg,-AdumpOnErrors,-AexceptionLineSeparator-ApermitMissingJdk,-AparseAllJdk-AslowTypecheckingSeconds-Aversion,-AprintGitProperties- You can pass an option to only a particular checker (not all checkers) by using an underscore prefix.
Other improvements include thousands of enhancements and bug fixes -- too many to list here.
Implementation details
All previously-deprecated methods and classes have been removed. If your project builds upon the Checker Framework, we suggest that you upgrade to version 3.55.1, resolve all the deprecation warnings, then upgrade to version4.0.0.