inthashtable.java

一个java操作pdf文件的开发包,很好用的.

// IntHashtable - a Hashtable that uses ints as the keys
//
// This is 90% based on JavaSoft's java.util.Hashtable.
//
// Visit the ACME Labs Java page for up-to-date versions of this and other
// fine Java utilities: http://www.acme.com/java/

package com.lowagie.text.pdf;

import java.util.Arrays;

/// A Hashtable that uses ints as the keys.
// <P>
// Use just like java.util.Hashtable, except that the keys must be ints.
// This is much faster than creating a new Integer for each access.
// <P>
// <A HREF="/resources/classes/Acme/IntHashtable.java">Fetch the software.</A><BR>
// <A HREF="/resources/classes/Acme.tar.gz">Fetch the entire Acme package.</A>
// <P>
// @see java.util.Hashtable

public class IntHashtable {
    /// The hash table data.
    private IntHashtableEntry table[];
    
    /// The total number of entries in the hash table.
    private int count;
    
    /// Rehashes the table when count exceeds this threshold.
    private int threshold;
    
    /// The load factor for the hashtable.
    private float loadFactor;
    
    /// Constructs a new, empty hashtable with the specified initial
    // capacity and the specified load factor.
    // @param initialCapacity the initial number of buckets
    // @param loadFactor a number between 0.0 and 1.0, it defines
    //		the threshold for rehashing the hashtable into
    //		a bigger one.
    // @exception IllegalArgumentException If the initial capacity
    // is less than or equal to zero.
    // @exception IllegalArgumentException If the load factor is
    // less than or equal to zero.
    public IntHashtable( int initialCapacity, float loadFactor ) {
        if ( initialCapacity <= 0 || loadFactor <= 0.0 )
            throw new IllegalArgumentException();
        this.loadFactor = loadFactor;
        table = new IntHashtableEntry[initialCapacity];
        threshold = (int) ( initialCapacity * loadFactor );
    }
    
    /// Constructs a new, empty hashtable with the specified initial
    // capacity.
    // @param initialCapacity the initial number of buckets
    public IntHashtable( int initialCapacity ) {
        this( initialCapacity, 0.75f );
    }
    
    /// Constructs a new, empty hashtable. A default capacity and load factor
    // is used. Note that the hashtable will automatically grow when it gets
    // full.
    public IntHashtable() {
        this( 101, 0.75f );
    }
    
    /// Returns the number of elements contained in the hashtable.
    public int size() {
        return count;
    }
    
    /// Returns true if the hashtable contains no elements.
    public boolean isEmpty() {
        return count == 0;
    }
    
    /// Returns true if the specified object is an element of the hashtable.
    // This operation is more expensive than the containsKey() method.
    // @param value the value that we are looking for
    // @exception NullPointerException If the value being searched
    // for is equal to null.
    // @see IntHashtable#containsKey
    public boolean contains( int value ) {
        IntHashtableEntry tab[] = table;
        for ( int i = tab.length ; i-- > 0 ; ) {
            for ( IntHashtableEntry e = tab[i] ; e != null ; e = e.next ) {
                if ( e.value == value )
                    return true;
            }
        }
        return false;
    }
    
    /// Returns true if the collection contains an element for the key.
    // @param key the key that we are looking for
    // @see IntHashtable#contains
    public boolean containsKey( int key ) {
        IntHashtableEntry tab[] = table;
        int hash = key;
        int index = ( hash & 0x7FFFFFFF ) % tab.length;
        for ( IntHashtableEntry e = tab[index] ; e != null ; e = e.next ) {
            if ( e.hash == hash && e.key == key )
                return true;
        }
        return false;
    }
    
    /// Gets the object associated with the specified key in the
    // hashtable.
    // @param key the specified key
    // @returns the element for the key or null if the key
    // 		is not defined in the hash table.
    // @see IntHashtable#put
    public int get( int key ) {
        IntHashtableEntry tab[] = table;
        int hash = key;
        int index = ( hash & 0x7FFFFFFF ) % tab.length;
        for ( IntHashtableEntry e = tab[index] ; e != null ; e = e.next ) {
            if ( e.hash == hash && e.key == key )
                return e.value;
        }
        return 0;
    }
    
    /// Rehashes the content of the table into a bigger table.
    // This method is called automatically when the hashtable's
    // size exceeds the threshold.
    protected void rehash() {
        int oldCapacity = table.length;
        IntHashtableEntry oldTable[] = table;
        
        int newCapacity = oldCapacity * 2 + 1;
        IntHashtableEntry newTable[] = new IntHashtableEntry[newCapacity];
        
        threshold = (int) ( newCapacity * loadFactor );
        table = newTable;
        
        for ( int i = oldCapacity ; i-- > 0 ; ) {
            for ( IntHashtableEntry old = oldTable[i] ; old != null ; ) {
                IntHashtableEntry e = old;
                old = old.next;
                
                int index = ( e.hash & 0x7FFFFFFF ) % newCapacity;
                e.next = newTable[index];
                newTable[index] = e;
            }
        }
    }
    
    /// Puts the specified element into the hashtable, using the specified
    // key.  The element may be retrieved by doing a get() with the same key.
    // The key and the element cannot be null.
    // @param key the specified key in the hashtable
    // @param value the specified element
    // @exception NullPointerException If the value of the element
    // is equal to null.
    // @see IntHashtable#get
    // @return the old value of the key, or null if it did not have one.
    public int put( int key, int value ) {
        // Makes sure the key is not already in the hashtable.
        IntHashtableEntry tab[] = table;
        int hash = key;
        int index = ( hash & 0x7FFFFFFF ) % tab.length;
        for ( IntHashtableEntry e = tab[index] ; e != null ; e = e.next ) {
            if ( e.hash == hash && e.key == key ) {
                int old = e.value;
                e.value = value;
                return old;
            }
        }
        
        if ( count >= threshold ) {
            // Rehash the table if the threshold is exceeded.
            rehash();
            return put( key, value );
        }
        
        // Creates the new entry.
        IntHashtableEntry e = new IntHashtableEntry();
        e.hash = hash;
        e.key = key;
        e.value = value;
        e.next = tab[index];
        tab[index] = e;
        ++count;
        return 0;
    }
    
    /// Removes the element corresponding to the key. Does nothing if the
    // key is not present.
    // @param key the key that needs to be removed
    // @return the value of key, or null if the key was not found.
    public int remove( int key ) {
        IntHashtableEntry tab[] = table;
        int hash = key;
        int index = ( hash & 0x7FFFFFFF ) % tab.length;
        for ( IntHashtableEntry e = tab[index], prev = null ; e != null ; prev = e, e = e.next ) {
            if ( e.hash == hash && e.key == key ) {
                if ( prev != null )
                    prev.next = e.next;
                else
                    tab[index] = e.next;
                --count;
                return e.value;
            }
        }
        return 0;
    }
    
    /// Clears the hash table so that it has no more elements in it.
    public void clear() {
        IntHashtableEntry tab[] = table;
        for ( int index = tab.length; --index >= 0; )
            tab[index] = null;
        count = 0;
    }
    
    public int[] toOrderedKeys() {
        int res[] = new int[count];
        int ptr = 0;
        int index = table.length;
        IntHashtableEntry entry = null;
        while (true) {
            if (entry == null)
                while ((index-- > 0) && ((entry = table[index]) == null));
            if (entry == null)
                break;
            IntHashtableEntry e = entry;
            entry = e.next;
            res[ptr++] = e.key;
        }
        Arrays.sort(res);
        return res;
    }
    
    class IntHashtableEntry {
        int hash;
        int key;
        int value;
        IntHashtableEntry next;
    }    
}