private void initializeDefaultProbabilityParameters() {
        priorMagicFileType = 0.5f;
        priorExtensionFileType = 0.5f;
        priorMetaFileType = 0.5f;
        magic_trust = DEFAULT_MAGIC_TRUST;
        extension_trust = DEFAULT_EXTENSION_TRUST;
        meta_trust = DEFAULT_META_TRUST;

        // probability of the type detected by magic test given that the type is
        // not the detected type. The default is taken by 1 - the magic trust
        magic_neg = 1 - DEFAULT_MAGIC_TRUST;
        // probability of the type detected by extension test given that the
        // type is not the type detected by extension test
        extension_neg = 1 - DEFAULT_EXTENSION_TRUST;
        // same as above; but it could be customized to suffice different use.
        meta_neg = 1 - DEFAULT_META_TRUST;
        threshold = 0.5001f;
    }
Initilize probability parameters with default values;
tika-core/src/main/java/org/apache/tika/mime/ProbabilisticMimeDetectionSelector.java