http://github.com/google/tink: Tink is a small cryptographic library that provides a safe, simple, agile and fast way to accomplish some common cryptographic tasks. 
// Copyright 2017 Google Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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////////////////////////////////////////////////////////////////////////////////

package com.google.crypto.tink;

import java.security.GeneralSecurityException;


Basic interface for wrapping a primitive.

A PrimitiveSet can be wrapped by a single primitive in order to fulfil a cryptographic task. This is done by the PrimitiveWrapper. Whenever a new primitive type is added to Tink, the user should define a new PrimitiveWrapper and register it by calling 
com.google.crypto.tink.Registry#registerPrimitiveWrapper. 
The primitive wrapper wraps primitives of type B into primitives of type P. Often, these are the same classes, but in some cases they may not be. There can only be one wrapper for each result primitive P (as Tink needs to know how to generate a P), but there may be many wrapping the same B. 
/**
 * Basic interface for wrapping a primitive.
 *
 * <p>A PrimitiveSet can be wrapped by a single primitive in order to fulfil a cryptographic task.
 * This is done by the PrimitiveWrapper. Whenever a new primitive type is added to Tink, the user
 * should define a new PrimitiveWrapper and register it by calling {@code
 * com.google.crypto.tink.Registry#registerPrimitiveWrapper}.
 *
 * <p>The primitive wrapper wraps primitives of type {@code B} into primitives of type {@code P}.
 * Often, these are the same classes, but in some cases they may not be. There can only be one
 * wrapper for each result primitive {@code P} (as Tink needs to know how to generate a {@code P}),
 * but there may be many wrapping the same {@code B}.
 */
public interface PrimitiveWrapper<B, P> {
  
Wraps a PrimitiveSet and returns a single instance. This has to be implemented when a new primitive type is added. 
/**
   * Wraps a {@code PrimitiveSet} and returns a single instance.
   *
   * This has to be implemented when a new primitive type is added. */
  P wrap(PrimitiveSet<B> set) throws GeneralSecurityException;

  
Returns the primitive class object of the primitive managed. Used for internal management. Should be implemented as return P.class; when implementing a wrapper creating objects of type P. 
/**
   * Returns the primitive class object of the primitive managed. Used for internal management.
   * Should be implemented as {@code return P.class;} when implementing a wrapper creating objects
   * of type {@code P}.
   */
  Class<P> getPrimitiveClass();

  
Returns the primitive class object of the primitive used to create B. Used for internal management. Should be implemented as return B.class;. 
/**
   * Returns the primitive class object of the primitive used to create B. Used for internal
   * management. Should be implemented as {@code return B.class;}.
   */
  Class<B> getInputPrimitiveClass();
}