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  *
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  * individuals on behalf of the Apache Software Foundation and was
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 package org.apache.jasper.xmlparser;

This class is a symbol table implementation that guarantees that strings used as identifiers are unique references. Multiple calls to addSymbol will always return the same string reference.

The symbol table performs the same task as String.intern() with the following differences:

  • 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.
  • 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 mostly unique. Strings with similar leading characters are especially prone to this poor hashing behavior.

Author(s):
Andy Clark
Version:
$Id: SymbolTable.java 515 2008-03-17 21:02:23Z jfrederic.clere@jboss.com $
 
 public class SymbolTable {
 
     //
     // Constants
     //
 
    
Default table size.
 
     protected static final int TABLE_SIZE = 101;
 
     //
     // Data
     //
 
    
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();
     }

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

Parameters:
symbol The new symbol.
 
    public String addSymbol(String symbol) {
        // search for identical symbol
        int bucket = hash(symbol) % ;
        int length = symbol.length();
        OUTER: for (Entry entry = [bucket]; entry != nullentry = entry.next) {
            if (length == entry.characters.length) {
                for (int i = 0; i < lengthi++) {
                    if (symbol.charAt(i) != entry.characters[i]) {
                        continue OUTER;
                    }
                }
                return entry.symbol;
            }
        }
        // create new entry
        Entry entry = new Entry(symbol[bucket]);
        [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.

Parameters:
buffer The buffer containing the new symbol.
offset The offset into the buffer of the new symbol.
length The length of the new symbol in the buffer.
    public String addSymbol(char[] bufferint offsetint length) {
        // search for identical symbol
        int bucket = hash(bufferoffsetlength) % ;
        OUTER: for (Entry entry = [bucket]; entry != nullentry = entry.next) {
            if (length == entry.characters.length) {
                for (int i = 0; i < lengthi++) {
                    if (buffer[offset + i] != entry.characters[i]) {
                        continue OUTER;
                    }
                }
                return entry.symbol;
            }
        }
        // add new entry
        Entry entry = new Entry(bufferoffsetlength[bucket]);
        [bucket] = entry;
        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 hash(char[],int,int) method when called with the character array that comprises the symbol string.

Parameters:
symbol The symbol to hash.
    public int hash(String symbol) {
        int code = 0;
        int length = symbol.length();
        for (int i = 0; i < lengthi++) {
            code = code * 37 + symbol.charAt(i);
        }
        return code & 0x7FFFFFF;
    } // 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 hash(String) method when called with the string object created from the symbol information.

Parameters:
buffer The character buffer containing the symbol.
offset The offset into the character buffer of the start of the symbol.
length The length of the symbol.
    public int hash(char[] bufferint offsetint length) {
        int code = 0;
        for (int i = 0; i < lengthi++) {
            code = code * 37 + buffer[offset + i];
        }
        return code & 0x7FFFFFF;
    } // hash(char[],int,int):int

    
Returns true if the symbol table already contains the specified symbol.

Parameters:
symbol The symbol to look for.
    public boolean containsSymbol(String symbol) {
        // search for identical symbol
        int bucket = hash(symbol) % ;
        int length = symbol.length();
        OUTER: for (Entry entry = [bucket]; entry != nullentry = entry.next) {
            if (length == entry.characters.length) {
                for (int i = 0; i < lengthi++) {
                    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.

Parameters:
buffer The buffer containing the symbol to look for.
offset The offset into the buffer.
length The length of the symbol in the buffer.
    public boolean containsSymbol(char[] bufferint offsetint length) {
        // search for identical symbol
        int bucket = hash(bufferoffsetlength) % ;
        OUTER: for (Entry entry = [bucket]; entry != nullentry = entry.next) {
            if (length == entry.characters.length) {
                for (int i = 0; i < lengthi++) {
                    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;

        
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 symbolEntry next) {
            this. = symbol.intern();
             = new char[symbol.length()];
            symbol.getChars(0, ., 0);
            this. = next;
        }

        
Constructs a new entry from the specified symbol information and next entry reference.
        public Entry(char[] chint offsetint lengthEntry next) {
             = new char[length];
            System.arraycopy(choffset, 0, length);
             = new String().intern();
            this. = next;
        }
    } // class Entry
// class SymbolTable
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