inthashtable.java

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// 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 Acme;

import java.util.Dictionary;
import java.util.Enumeration;
import java.util.NoSuchElementException;

/// 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 extends Dictionary implements Cloneable {
    /// 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 an enumeration of the hashtable's keys.
    // @see IntHashtable#elements
    public synchronized Enumeration keys() {
        return new IntHashtableEnumerator(table, true);
    }

    /// Returns an enumeration of the elements. Use the Enumeration
    // methods
    // on the returned object to fetch the elements sequentially.
    // @see IntHashtable#keys
    public synchronized Enumeration elements() {
        return new IntHashtableEnumerator(table, false);
    }

    /// 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 synchronized boolean contains(Object value) {
        if (value == null)
            throw new NullPointerException();
        IntHashtableEntry tab[] = table;
        for (int i = tab.length; i-- > 0;) {
            for (IntHashtableEntry e = tab[i]; e != null; e = e.next) {
                if (e.value.equals(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 synchronized 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 synchronized Object 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 null;
    }

    /// A get method that takes an Object, for compatibility with
    // java.util.Dictionary. The Object must be an Integer.
    public Object get(Object okey) {
        if (!(okey instanceof Integer))
            throw new InternalError("key is not an Integer");
        Integer ikey = (Integer) okey;
        int key = ikey.intValue();
        return get(key);
    }

    /// 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 synchronized Object put(int key, Object value) {
        // Make sure the value is not null.
        if (value == null)
            throw new NullPointerException();

        // 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) {
                Object 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 null;
    }

    /// A put method that takes an Object, for compatibility with
    // java.util.Dictionary. The Object must be an Integer.
    public Object put(Object okey, Object value) {
        if (!(okey instanceof Integer))
            throw new InternalError("key is not an Integer");
        Integer ikey = (Integer) okey;
        int key = ikey.intValue();
        return put(key, value);
    }

    /// 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 synchronized Object 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 null;
    }

    /// A remove method that takes an Object, for compatibility with
    // java.util.Dictionary. The Object must be an Integer.
    public Object remove(Object okey) {
        if (!(okey instanceof Integer))
            throw new InternalError("key is not an Integer");
        Integer ikey = (Integer) okey;
        int key = ikey.intValue();
        return remove(key);
    }

    /// Clears the hash table so that it has no more elements in it.
    public synchronized void clear() {
        IntHashtableEntry tab[] = table;
        for (int index = tab.length; --index >= 0;)
            tab[index] = null;
        count = 0;
    }

    /// Creates a clone of the hashtable. A shallow copy is made,
    // the keys and elements themselves are NOT cloned. This is a
    // relatively expensive operation.
    public synchronized Object clone() {
        try {
            IntHashtable t = (IntHashtable) super.clone();
            t.table = new IntHashtableEntry[table.length];
            for (int i = table.length; i-- > 0;)
                t.table[i] = (table[i] != null) ? (IntHashtableEntry) table[i].clone()
                        : null;
            return t;
        } catch (CloneNotSupportedException e) {
            // This shouldn't happen, since we are Cloneable.
            throw new InternalError();
        }
    }

    /// Converts to a rather lengthy String.
    public synchronized String toString() {
        int max = size() - 1;
        StringBuffer buf = new StringBuffer();
        Enumeration k = keys();
        Enumeration e = elements();
        buf.append("{");

        for (int i = 0; i <= max; ++i) {
            String s1 = k.nextElement().toString();
            String s2 = e.nextElement().toString();
            buf.append(s1 + "=" + s2);
            if (i < max)
                buf.append(", ");
        }
        buf.append("}");
        return buf.toString();
    }
}

class IntHashtableEntry {
    int hash;
    int key;
    Object value;
    IntHashtableEntry next;

    protected Object clone() {
        IntHashtableEntry entry = new IntHashtableEntry();
        entry.hash = hash;
        entry.key = key;
        entry.value = value;
        entry.next = (next != null) ? (IntHashtableEntry) next.clone() : null;
        return entry;
    }
}

class IntHashtableEnumerator implements Enumeration {
    boolean keys;
    int index;
    IntHashtableEntry table[];
    IntHashtableEntry entry;

    IntHashtableEnumerator(IntHashtableEntry table[], boolean keys) {
        this.table = table;
        this.keys = keys;
        this.index = table.length;
    }

    public boolean hasMoreElements() {
        if (entry != null)
            return true;
        while (index-- > 0)
            if ((entry = table[index]) != null)
                return true;
        return false;
    }

    public Object nextElement() {
        if (entry == null)
            while ((index-- > 0) && ((entry = table[index]) == null))
                ;
        if (entry != null) {
            IntHashtableEntry e = entry;
            entry = e.next;
            return keys ? new Integer(e.key) : e.value;
        }
        throw new NoSuchElementException("IntHashtableEnumerator");
    }
}