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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def default_java_namespace(self, target):
 """Returns the default_java_namespace used for Thrift generation. :param target: The target to extract the default_java_namespace from. :type target: :class:`pants.backend.codegen.targets.java_thrift_library.JavaThriftLibrary` :returns: The default Java namespace used when not specified in the IDL. :rtype: string """

    self._check_target(target)
    return target.default_java_namespace or self._default_default_java_namespace