Initial revision

From-SVN: r26263

libjava/java/util/Hashtable.java

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+/* Copyright (C) 1998, 1999  Cygnus Solutions
+
+   This file is part of libgcj.
+
+This software is copyrighted work licensed under the terms of the
+Libgcj License.  Please consult the file "LIBGCJ_LICENSE" for
+details.  */
+
+package java.util;
+
+import java.io.Serializable;
+
+/**
+ * @author Warren Levy <warrenl@cygnus.com>
+ * @date September 24, 1998.
+ */
+/* Written using "Java Class Libraries", 2nd edition, ISBN 0-201-31002-3
+ * "The Java Language Specification", ISBN 0-201-63451-1
+ * plus online API docs for JDK 1.2 beta from http://www.javasoft.com.
+ * Status:  Believed complete and correct
+ */
+
+class HashtableEntry
+{
+  public Object key;
+  public Object value;
+  public HashtableEntry nextEntry = null;
+
+  public HashtableEntry(Object key, Object value)
+  {
+    this.key = key;
+    this.value = value;
+  }
+}
+
+class HashtableEnumeration implements Enumeration
+{
+  // TBD: Enumeration is not safe if new elements are put in the table as
+  // this could cause a rehash and we'd completely lose our place.  Even
+  // without a rehash, it is undetermined if a new element added would
+  // appear in the enumeration.  The spec says nothing about this, but
+  // the "Java Class Libraries" book infers that modifications to the
+  // hashtable during enumeration causes indeterminate results.  Don't do it!
+  // A safer way would be to make a copy of the table (e.g. into a vector)
+  // but this is a fair bit  more expensive.
+  private HashtableEntry[] bucket;
+  private int bucketIndex;
+  private HashtableEntry elem;
+  private int enumCount;
+  private int size;
+  private boolean values;
+
+  public HashtableEnumeration(HashtableEntry[] bkt, int sz, boolean isValues)
+  {
+    bucket = bkt;
+    bucketIndex = -1;
+    enumCount = 0;
+    elem = null;
+    size = sz;
+    values = isValues;
+  }
+
+  public boolean hasMoreElements()
+  {
+    return enumCount < size;
+  }
+
+  public Object nextElement()
+  {
+    if (!hasMoreElements())
+      throw new NoSuchElementException();
+
+    // Find next element
+    if (elem != null)		// In the middle of a bucket
+      elem = elem.nextEntry;
+    while (elem == null)	// Find the next non-empty bucket
+      elem = bucket[++bucketIndex];
+
+    enumCount++;
+    return values ? elem.value : elem.key;
+  }
+}
+
+// TBD: The algorithm used here closely reflects what is described in
+// the "Java Class Libraries" book.  The "Java Language Spec" is much
+// less specific about the implementation.  Because of this freedom
+// provided by the actual spec, hash table algorithms should be
+// investigated to see if there is a better alternative to this one.
+
+// TODO12:
+// public class Hashtable extends Dictionary
+//			implements Map, Cloneable, Serializable
+
+public class Hashtable extends Dictionary implements Cloneable, Serializable
+{
+  private HashtableEntry bucket[];
+  private float loadFactor;
+  private int hsize = 0;
+
+  public Hashtable()
+  {
+    // The "Java Class Libraries" book (p. 919) says that initial size in this
+    // case is 101 (a prime number to increase the odds of even distribution).
+    this(101, 0.75F);
+  }
+
+  public Hashtable(int initialSize)
+  {
+    this(initialSize, 0.75F);
+  }
+
+  public Hashtable(int initialSize, float loadFactor)
+  {
+    if (initialSize < 0 || loadFactor <= 0.0 || loadFactor > 1.0)
+      throw new IllegalArgumentException();
+
+    bucket = new HashtableEntry[initialSize];
+    this.loadFactor = loadFactor;
+  }
+
+  // TODO12:
+  // public Hashtable(Map t)
+  // {
+  // }
+
+  public synchronized void clear()
+  {
+    // Aid the GC by nulling out the entries in the hash table.
+    for (int i = 0; i < bucket.length; i++)
+      {
+        HashtableEntry elem = bucket[i];
+	bucket[i] = null;			// May already be null.
+	while (elem != null)
+	  {
+	    HashtableEntry next = elem.nextEntry;
+	    elem.nextEntry = null;		// May already be null.
+	    elem = next;
+	  }
+      }
+    hsize = 0;
+  }
+
+  public synchronized Object clone()
+  {
+    // New hashtable will have same initialCapacity and loadFactor.
+    Hashtable newTable = new Hashtable(bucket.length, loadFactor);
+
+    HashtableEntry newElem, prev = null;
+    for (int i = 0; i < bucket.length; i++)
+      for (HashtableEntry elem = bucket[i]; elem != null; elem = elem.nextEntry)
+	{
+	  // An easy but expensive method is newTable.put(elem.key, elem.value);
+	  // Since the hash tables are the same size, the buckets and collisions
+	  // will be the same in the new one, so we can just clone directly.
+	  // This is much cheaper than using put.
+	  newElem = new HashtableEntry(elem.key, elem.value);
+	  if (newTable.bucket[i] == null)
+	    prev = newTable.bucket[i] = newElem;
+	  else
+	    prev = prev.nextEntry = newElem;
+	}
+
+    newTable.hsize = this.hsize;
+    return newTable;
+  }
+
+  public synchronized boolean contains(Object value) throws NullPointerException
+  {
+    // An exception is thrown here according to the JDK 1.2 doc.
+    if (value == null)
+      throw new NullPointerException();
+
+    for (int i = 0; i < bucket.length; i++)
+      for (HashtableEntry elem = bucket[i]; elem != null; elem = elem.nextEntry)
+	if (elem.value.equals(value))
+	  return true;
+
+    return false;
+  }
+
+  public synchronized boolean containsKey(Object key)
+  {
+    // The Map interface mandates that we throw this.
+    if (key == null)
+      throw new NullPointerException ();
+
+    for (HashtableEntry elem = bucket[Math.abs(key.hashCode()
+					       % bucket.length)];
+	 elem != null; elem = elem.nextEntry)
+      if (elem.key.equals(key))
+	return true;
+
+    return false;
+  }
+
+  public synchronized Enumeration elements()
+  {
+    return new HashtableEnumeration(bucket, hsize, true);
+  }
+
+  public synchronized Object get(Object key)
+  {
+    // The Dictionary interface mandates that get() throw a
+    // NullPointerException if key is null.
+    if (key == null)
+      throw new NullPointerException ();
+
+    for (HashtableEntry elem = bucket[Math.abs (key.hashCode()
+						% bucket.length)];
+	 elem != null; elem = elem.nextEntry)
+      if (elem.key.equals(key))
+	return elem.value;
+
+    return null;
+  }
+
+  public boolean isEmpty()
+  {
+    return this.hsize <= 0;
+  }
+
+  public synchronized Enumeration keys()
+  {
+    return new HashtableEnumeration(bucket, hsize, false);
+  }
+
+  public synchronized Object put(Object key, Object value)
+				throws NullPointerException
+  {
+    if (key == null || value == null)
+      throw new NullPointerException();
+
+    HashtableEntry prevElem = null;
+    final int index = Math.abs(key.hashCode() % bucket.length);
+
+    for (HashtableEntry elem = bucket[index]; elem != null;
+	 prevElem = elem, elem = elem.nextEntry)
+      if (elem.key.equals(key))
+	{
+	  // Update with the new value and then return the old one.
+	  Object oldVal = elem.value;
+	  elem.value = value;
+	  return oldVal;
+	}
+
+    // At this point, we know we need to add a new element.
+    HashtableEntry newElem = new HashtableEntry(key, value);
+    if (bucket[index] == null)
+      bucket[index] = newElem;
+    else
+      prevElem.nextEntry = newElem;
+
+    if (++hsize > loadFactor * bucket.length)
+      rehash();
+
+    return null;
+  }
+
+  protected void rehash()
+  {
+    // Create a new table which is twice the size (plus one) of the old.
+    // One is added to make the new array length odd so it thus has at least
+    // a (small) possibility of being a prime number.
+    HashtableEntry oldBucket[] = bucket;
+    bucket = new HashtableEntry[bucket.length * 2 + 1];
+
+    // Copy over each entry into the new table
+    HashtableEntry elem;
+    for (int i = 0; i < oldBucket.length; i++)
+      for (elem = oldBucket[i]; elem != null; elem = elem.nextEntry)
+	{
+	  // Calling put(elem.key, elem.value); would seem like the easy way
+	  // but it is dangerous since put increases 'hsize' and calls rehash!
+	  // This could become infinite recursion under the right
+	  // circumstances.  Instead, we'll add the element directly; this is a
+	  // bit more efficient than put since the data is already verified.
+    	  final int index = Math.abs(elem.key.hashCode() % bucket.length);
+	  HashtableEntry newElem = new HashtableEntry(elem.key, elem.value);
+	  if (bucket[index] == null)
+	    bucket[index] = newElem;
+	  else
+	    {
+	      // Since this key can't already be in the table, just add this
+	      // in at the top of the bucket.
+	      newElem.nextEntry = bucket[index];
+	      bucket[index] = newElem;
+	    }
+	}
+  }
+
+  public synchronized Object remove(Object key)
+  {
+    // TBD: Hmm, none of the various docs say to throw an exception here.
+    if (key == null)
+      return null;
+
+    Object retval;
+    HashtableEntry prevElem = null;
+    final int index = Math.abs(key.hashCode() % bucket.length);
+
+    for (HashtableEntry elem = bucket[index]; elem != null;
+	 prevElem = elem, elem = elem.nextEntry)
+      if (elem.key.equals(key))
+	{
+	  retval = elem.value;
+	  if (prevElem == null)
+	    bucket[index] = elem.nextEntry;
+	  else
+	    prevElem.nextEntry = elem.nextEntry;
+	  --hsize;
+	  return retval;
+	}
+
+    return null;
+  }
+
+  public int size()
+  {
+    return this.hsize;
+  }
+
+  public synchronized String toString()
+  {
+    // Following the Java Lang Spec 21.5.4 (p. 636).
+
+    Enumeration keys = keys();
+    Enumeration values = elements();
+
+    // Prepend first element with open bracket
+    StringBuffer result = new StringBuffer("{");
+
+    // add first element if one exists
+    // TBD: Seems like it is more efficient to catch the exception than
+    // to call hasMoreElements each time around.
+    try
+    {
+      result.append(keys.nextElement().toString() + "=" +
+		values.nextElement().toString());
+    }
+    catch (NoSuchElementException ex)
+    {
+    }
+
+    // Prepend subsequent elements with ", "
+    try
+    {
+      while (true)
+        result.append(", " + keys.nextElement().toString() + "=" +
+		values.nextElement().toString());
+    }
+    catch (NoSuchElementException ex)
+    {
+    }
+
+    // Append last element with closing bracket
+    result.append("}");
+    return result.toString();
+  }
+
+  // TODO12:
+  // public Set entrySet()
+  // {
+  // }
+
+  // TODO12:
+  // public Set keySet()
+  // {
+  // }
+
+  // Since JDK 1.2:
+  // This method is identical to contains but is part of the 1.2 Map interface.
+  // TBD: Should contains return containsValue instead?  Depends on which
+  // will be called more typically.
+  public synchronized boolean containsValue(Object value)
+  {
+    return this.contains(value);
+  }
+
+  // TODO12:
+  // public boolean equals(Object o)
+  // {
+  // }
+
+  // TODO12:
+  // public boolean hashCode()
+  // {
+  // }
+
+  // TODO12:
+  // public void putAll(Map t)
+  // {
+  // }
+
+  // TODO12:
+  // public Collection values()
+  // {
+  // }
+}