Both, the consistency check and the file statistics are part of the db4o-X.XX-optional-java5 jar-file. To run the tool you need to have it and the core jar in the class-path. As alternative use the db4o-X.XX-all-java5 jar, which contains all dependencies.
To run consistency checks use the com.db4o.consistency.ConsistencyChecker class, like this:
java -cp db4oX-X.XX-all-java5.jar com.db4o.consistency.ConsistencyChecker databaseFile.db4o
This consistency check doesn't check the content of objects. It only checks if the overall structure of the database file is still intact. Also it doesn't offer any repair functionality. It only tells you if the file is corrupted or not.
To run consistency checks use the com.db4o.filestats.FileUsageStatsCollector class, like this:
java -cp db4oX-X.XX-all-java5.jar com.db4o.filestats.FileUsageStatsCollector databaseFile.db4o
The file statistics return the space usage of objects, indexes etc in bytes. It also returns the statistics for internal objects, managed by db4o.