since this class is new, immediately mark it package protected: it is

the implementation of JavaToolchain interface (even if the interface is
empty at the moment)

maven-core/src/main/java/org/apache/maven/toolchain/java/JavaToolchainImpl.java

@@ -29,12 +29,11 @@ import org.codehaus.plexus.util.Os;
 
 /**
  * JDK toolchain implementation.
- * <strong>Note:</strong> This is an internal component whose interface can change without prior notice.
  *
  * @author Milos Kleint
  * @since 2.0.9, renamed from DefaultJavaToolChain in 3.2.4
  */
-public class JavaToolchainImpl
+class JavaToolchainImpl
     extends DefaultToolchain
     implements JavaToolchain
 {