Java example source code file (SymbolTable.java)

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Java - Java tags/keywords

entry, outer, string, symboltable, table_size

The SymbolTable.java Java example source code

/*
 * Copyright (c) 2003, 2013, Oracle and/or its affiliates. All rights reserved.
 */

/*
 * Copyright 2005 The Apache Software Foundation.
 *
 * 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.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.sun.org.apache.xerces.internal.util;

/**
 * This class is a symbol table implementation that guarantees that
 * strings used as identifiers are unique references. Multiple calls
 * to <code>addSymbol will always return the same string
 * reference.
 * <p>
 * The symbol table performs the same task as <code>String.intern()
 * with the following differences:
 * <ul>
 *  <li>
 *   A new string object does not need to be created in order to
 *   retrieve a unique reference. Symbols can be added by using
 *   a series of characters in a character array.
 *  </li>
 *  <li>
 *   Users of the symbol table can provide their own symbol hashing
 *   implementation. For example, a simple string hashing algorithm
 *   may fail to produce a balanced set of hashcodes for symbols
 *   that are <em>mostly unique. Strings with similar leading
 *   characters are especially prone to this poor hashing behavior.
 *  </li>
 * </ul>
 *
 * @see SymbolHash
 *
 * @author Andy Clark
 *
 */
public class SymbolTable {

    //
    // Constants
    //

    /** Default table size. */
    protected static final int TABLE_SIZE = 173;


    /** Buckets. */
    protected Entry[] fBuckets = null;

    // actual table size
    protected int fTableSize;

    //
    // Constructors
    //

    /** Constructs a symbol table with a default number of buckets. */
    public SymbolTable() {
        this(TABLE_SIZE);
    }

    /** Constructs a symbol table with a specified number of buckets. */
    public SymbolTable(int tableSize) {
        fTableSize = tableSize;
        fBuckets = new Entry[fTableSize];
    }

    //
    // Public methods
    //

    /**
     * Adds the specified symbol to the symbol table and returns a
     * reference to the unique symbol. If the symbol already exists,
     * the previous symbol reference is returned instead, in order
     * guarantee that symbol references remain unique.
     *
     * @param symbol The new symbol.
     */
    public String addSymbol(String symbol) {

        // search for identical symbol
        final int hash = hash(symbol);
        final int bucket = hash % fTableSize;
        final int length = symbol.length();
        OUTER: for (Entry entry = fBuckets[bucket]; entry != null; entry = entry.next) {
            if (length == entry.characters.length && hash == entry.hashCode) {
                if(symbol.regionMatches(0,entry.symbol,0,length)){
                    return entry.symbol;
                }
                else{
                    continue OUTER;
                }
                /**
                for (int i = 0; i < length; i++) {
                    if (symbol.charAt(i) != entry.characters[i]) {
                        continue OUTER;
                    }
                }
                symbolAsArray = entry.characters;
                return entry.symbol;
                 */
            }
        }

        // create new entry
        Entry entry = new Entry(symbol, fBuckets[bucket]);
        entry.hashCode = hash;
        fBuckets[bucket] = entry;
        return entry.symbol;

    } // addSymbol(String):String

    /**
     * Adds the specified symbol to the symbol table and returns a
     * reference to the unique symbol. If the symbol already exists,
     * the previous symbol reference is returned instead, in order
     * guarantee that symbol references remain unique.
     *
     * @param buffer The buffer containing the new symbol.
     * @param offset The offset into the buffer of the new symbol.
     * @param length The length of the new symbol in the buffer.
     */
    public String addSymbol(char[] buffer, int offset, int length) {
        // search for identical symbol
        int hash = hash(buffer, offset, length);
        int bucket = hash % fTableSize;
        OUTER: for (Entry entry = fBuckets[bucket]; entry != null; entry = entry.next) {
            if (length == entry.characters.length && hash ==entry.hashCode) {
                for (int i = 0; i < length; i++) {
                    if (buffer[offset + i] != entry.characters[i]) {
                        continue OUTER;
                    }
                }
                return entry.symbol;
            }
        }

        // add new entry
        Entry entry = new Entry(buffer, offset, length, fBuckets[bucket]);
        fBuckets[bucket] = entry;
        entry.hashCode = hash;
        return entry.symbol;

    } // addSymbol(char[],int,int):String

    /**
     * Returns a hashcode value for the specified symbol. The value
     * returned by this method must be identical to the value returned
     * by the <code>hash(char[],int,int) method when called
     * with the character array that comprises the symbol string.
     *
     * @param symbol The symbol to hash.
     */
    public int hash(String symbol) {

        int code = 0;
        int length = symbol.length();
        for (int i = 0; i < length; i++) {
            code = code * 37 + symbol.charAt(i);
        }
        return code & 0x7FFFFFFF;

    } // hash(String):int

    /**
     * Returns a hashcode value for the specified symbol information.
     * The value returned by this method must be identical to the value
     * returned by the <code>hash(String) method when called
     * with the string object created from the symbol information.
     *
     * @param buffer The character buffer containing the symbol.
     * @param offset The offset into the character buffer of the start
     *               of the symbol.
     * @param length The length of the symbol.
     */
    public int hash(char[] buffer, int offset, int length) {

        int code = 0;
        for (int i = 0; i < length; i++) {
            code = code * 37 + buffer[offset + i];
        }
        return code & 0x7FFFFFFF;

    } // hash(char[],int,int):int

    /**
     * Returns true if the symbol table already contains the specified
     * symbol.
     *
     * @param symbol The symbol to look for.
     */
    public boolean containsSymbol(String symbol) {

        // search for identical symbol
        int hash = hash(symbol);
        int bucket = hash % fTableSize;
        int length = symbol.length();
        OUTER: for (Entry entry = fBuckets[bucket]; entry != null; entry = entry.next) {
            if (length == entry.characters.length && hash == entry.hashCode) {
                if(symbol.regionMatches(0,entry.symbol,0,length)){
                    return true;
                }
                else {
                    continue OUTER;
                }
                /**
                for (int i = 0; i < length; i++) {
                    if (symbol.charAt(i) != entry.characters[i]) {
                        continue OUTER;
                    }
                }
                 return true;
                 */
            }
        }

        return false;

    } // containsSymbol(String):boolean

    /**
     * Returns true if the symbol table already contains the specified
     * symbol.
     *
     * @param buffer The buffer containing the symbol to look for.
     * @param offset The offset into the buffer.
     * @param length The length of the symbol in the buffer.
     */
    public boolean containsSymbol(char[] buffer, int offset, int length) {

        // search for identical symbol
        int hash = hash(buffer, offset, length) ;
        int bucket = hash % fTableSize;
        OUTER: for (Entry entry = fBuckets[bucket]; entry != null; entry = entry.next) {
            if (length == entry.characters.length && hash == entry.hashCode) {
                for (int i = 0; i < length; i++) {
                    if (buffer[offset + i] != entry.characters[i]) {
                        continue OUTER;
                    }
                }
                return true;
            }
        }

        return false;

    } // containsSymbol(char[],int,int):boolean


    //
    // Classes
    //

    /**
     * This class is a symbol table entry. Each entry acts as a node
     * in a linked list.
     */
    protected static final class Entry {

        //
        // Data
        //

        /** Symbol. */
        public String symbol;
        int hashCode = 0;

        /**
         * Symbol characters. This information is duplicated here for
         * comparison performance.
         */
        public char[] characters;

        /** The next entry. */
        public Entry next;

        //
        // Constructors
        //

        /**
         * Constructs a new entry from the specified symbol and next entry
         * reference.
         */
        public Entry(String symbol, Entry next) {
            this.symbol = symbol.intern();
            characters = new char[symbol.length()];
            symbol.getChars(0, characters.length, characters, 0);
            this.next = next;
        }

        /**
         * Constructs a new entry from the specified symbol information and
         * next entry reference.
         */
        public Entry(char[] ch, int offset, int length, Entry next) {
            characters = new char[length];
            System.arraycopy(ch, offset, characters, 0, length);
            symbol = new String(characters).intern();
            this.next = next;
        }

    } // class Entry

} // class SymbolTable