org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsStreamKey.java

/*
 * Copyright (C) 2011, Google Inc.
 * and other copyright owners as documented in the project's IP log.
 *
 * This program and the accompanying materials are made available
 * under the terms of the Eclipse Distribution License v1.0 which
 * accompanies this distribution, is reproduced below, and is
 * available at http://www.eclipse.org/org/documents/edl-v10.php
 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or
 * without modification, are permitted provided that the following
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 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 *
 * - Redistributions in binary form must reproduce the above
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 *   disclaimer in the documentation and/or other materials provided
 *   with the distribution.
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 * - Neither the name of the Eclipse Foundation, Inc. nor the
 *   names of its contributors may be used to endorse or promote
 *   products derived from this software without specific prior
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 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
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 * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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package org.eclipse.jgit.internal.storage.dfs;

import static java.nio.charset.StandardCharsets.UTF_8;

import java.util.Arrays;

/** Key used by {@link DfsBlockCache} to disambiguate streams. */
public abstract class DfsStreamKey {
	/**
	 * @param name
	 *            compute the key from a string name.
	 * @return key for {@code name}
	 */
	public static DfsStreamKey of(String name) {
		return of(name.getBytes(UTF_8));
	}

	/**
	 * @param name
	 *            compute the key from a byte array. The key takes ownership of
	 *            the passed {@code byte[] name}.
	 * @return key for {@code name}
	 */
	public static DfsStreamKey of(byte[] name) {
		return new ByteArrayDfsStreamKey(name);
	}

	final int hash;

	/**
	 * @param hash
	 *            hash of the other identifying components of the key.
	 */
	protected DfsStreamKey(int hash) {
		// Multiply by 31 here so we can more directly combine with another
		// value without doing the multiply there.
		this.hash = hash * 31;
	}

	/**
	 * Derive a new StreamKey based on this existing key.
	 *
	 * @param suffix
	 *            a derivation suffix.
	 * @return derived stream key.
	 */
	public abstract DfsStreamKey derive(String suffix);

	@Override
	public int hashCode() {
		return hash;
	}

	@Override
	public abstract boolean equals(Object o);

	@SuppressWarnings("boxing")
	@Override
	public String toString() {
		return String.format("DfsStreamKey[hash=%08x]", hash); //$NON-NLS-1$
	}

	private static final class ByteArrayDfsStreamKey extends DfsStreamKey {
		private final byte[] name;

		ByteArrayDfsStreamKey(byte[] name) {
			super(Arrays.hashCode(name));
			this.name = name;
		}

		@Override
		public DfsStreamKey derive(String suffix) {
			byte[] s = suffix.getBytes(UTF_8);
			byte[] n = Arrays.copyOf(name, name.length + s.length);
			System.arraycopy(s, 0, n, name.length, s.length);
			return new ByteArrayDfsStreamKey(n);
		}

		@Override
		public boolean equals(Object o) {
			if (o instanceof ByteArrayDfsStreamKey) {
				ByteArrayDfsStreamKey k = (ByteArrayDfsStreamKey) o;
				return hash == k.hash && Arrays.equals(name, k.name);
			}
			return false;
		}
	}
}