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Handful shortcuts for Java programming, Java 7 compatible.
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/*******************************************************************************
 * Copyright (C) 2009, 2015, Danilo Pianini and contributors
 * listed in the project's build.gradle or pom.xml file.
 *
 * This file is distributed under the terms of the Apache License, version 2.0
 *******************************************************************************/
package org.danilopianini.lang.util;

import java.io.Serializable;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.util.Objects;

import com.google.common.hash.HashCode;
import com.google.common.hash.HashFunction;
import com.google.common.hash.Hashing;

import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;

/**
 * This class wraps java.lang.String and provides faster equals(). Used
 * internally to ensure better performances. The faster comparison is realized
 * by computing a hash internally (currently using Murmur 3), so be aware that
 * collisions may happen.
 * 
 * @author Danilo Pianini
 * 
 */
public class FasterString implements Cloneable, Serializable, Comparable, CharSequence {

	private static final long serialVersionUID = -3490623928660729120L;
	private static final Charset CHARSET = StandardCharsets.UTF_8;
	private static final HashFunction HASHF = Hashing.murmur3_128();
	private static final byte ENCODING_BASE = 36;
	
	private String base;
	@SuppressFBWarnings(justification = "This hash is recomputed if needed after de-serialization.")
	private transient HashCode hash;
	private long hash64bit;
	private int hash32bit;
	private final String s;

	/**
	 * Clones this object.
	 * 
	 * @param string
	 *            the template for the clone
	 */
	public FasterString(final FasterString string) {
		s = string.s;
		hash64bit = string.hash64bit;
		hash32bit = string.hash32bit;
	}

	/**
	 * @param string
	 *            the String to wrap
	 */
	public FasterString(final String string) {
		Objects.requireNonNull(string);
		s = string;
	}

	@Override
	public char charAt(final int index) {
		return s.charAt(index);
	}

	@Override
	public FasterString clone() {
		/*
		 * State cannot change, no need to deep copy anything.
		 */
		return this;
	}

	@Override
	public int compareTo(final FasterString o) {
		return s.compareTo(o.s);
	}

	private void computeHashes() {
		hash = HASHF.hashBytes(s.getBytes(CHARSET));
		hash32bit = hash.asInt();
		hash64bit = hash.asLong();
	}

	/**
	 * Overloaded method.
	 * 
	 * @param fs
	 *            the FasterString to compare to
	 * @return true if equals
	 */
	public boolean equals(final FasterString fs) {
		return hashCode() == fs.hashCode()
				&& s.length() == fs.s.length()
				&& hash64bit == fs.hash64bit
				&& hash.equals(fs.hash);
	}

	@Override
	public boolean equals(final Object o) {
		return o instanceof FasterString && equals((FasterString) o);
	}

	/**
	 * @return a 64bit hash, computed with DJB2
	 */
	public long hash64() {
		if (hash == null) {
			computeHashes();
		}
		return hash64bit;
	}

	@Override
	public int hashCode() {
		if (hash == null) {
			computeHashes();
		}
		return hash32bit;
	}

	/**
	 * @return A Base64 encoded version of the hash
	 */
	public String hashToString() {
		if (base == null) {
			/*
			 * If hash32 is negative, it is necessary to sum 1. This is because
			 * -Integer.MIN_VALUE is equal to Integer.MIN_VALUE.
			 */
			final int h32 = hashCode() > 0 ? hash32bit : -(hash32bit + 1);
			final long h64 = hash64bit > 0 ? hash64bit : -(hash64bit + 1);
			base = Integer.toString(h32, ENCODING_BASE) + Long.toString(h64, ENCODING_BASE);
		}
		return base;
	}

	@Override
	public int length() {
		return s.length();
	}

	@Override
	public CharSequence subSequence(final int start, final int end) {
		return s.subSequence(start, end);
	}

	@Override
	public String toString() {
		return s;
	}

}