com.cedarsoftware.util.CompactSet Maven / Gradle / Ivy
package com.cedarsoftware.util;
import java.lang.reflect.Constructor;
import java.util.AbstractSet;
import java.util.Collection;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Objects;
import java.util.Set;
/**
* Often, memory may be consumed by lots of Maps or Sets (HashSet uses a HashMap to implement it's set). HashMaps
* and other similar Maps often have a lot of blank entries in their internal structures. If you have a lot of Maps
* in memory, perhaps representing JSON objects, large amounts of memory can be consumed by these empty Map entries.
*
* CompactSet is a Set that strives to reduce memory at all costs while retaining speed that is close to HashSet's speed.
* It does this by using only one (1) member variable (of type Object) and changing it as the Set grows. It goes from
* an Object[] to a Set when the size() of the Set crosses the threshold defined by the method compactSize() (defaults
* to 80). After the Set crosses compactSize() size, then it uses a Set (defined by the user) to hold the items. This
* Set is defined by a method that can be overridden, which returns a new empty Set() for use in the {@literal >} compactSize()
* state.
*
* Methods you may want to override:
*
* // Map you would like it to use when size() {@literal >} compactSize(). HashSet is default
* protected abstract Map{@literal <}K, V{@literal >} getNewMap();
*
* // If you want case insensitivity, return true and return new CaseInsensitiveSet or TreeSet(String.CASE_INSENSITIVE_PRDER) from getNewSet()
* protected boolean isCaseInsensitive() { return false; }
*
* // When size() {@literal >} than this amount, the Set returned from getNewSet() is used to store elements.
* protected int compactSize() { return 80; }
*
* This Set supports holding a null element.
*
* @author John DeRegnaucourt ([email protected])
*
* Copyright (c) Cedar Software LLC
*
* 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
*
* License
*
* 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.
*/
public class CompactSet extends AbstractSet
{
private static final String EMPTY_SET = "_︿_ψ_☼";
private static final String NO_ENTRY = EMPTY_SET;
private Object val = EMPTY_SET;
public CompactSet()
{
if (compactSize() < 2)
{
throw new IllegalStateException("compactSize() must be >= 2");
}
}
public CompactSet(Collection other)
{
this();
addAll(other);
}
public int size()
{
if (val instanceof Object[])
{ // 1 to compactSize
return ((Object[])val).length;
}
else if (val instanceof Set)
{ // > compactSize
return ((Set)val).size();
}
// empty
return 0;
}
public boolean isEmpty()
{
return val == EMPTY_SET;
}
private boolean compareItems(Object item, Object anItem)
{
if (item instanceof String)
{
if (anItem instanceof String)
{
if (isCaseInsensitive())
{
return ((String)anItem).equalsIgnoreCase((String) item);
}
else
{
return anItem.equals(item);
}
}
return false;
}
return Objects.equals(item, anItem);
}
@SuppressWarnings("unchecked")
public boolean contains(Object item)
{
if (val instanceof Object[])
{ // 1 to compactSize
Object[] entries = (Object[]) val;
for (Object entry : entries)
{
if (compareItems(item, entry))
{
return true;
}
}
return false;
}
else if (val instanceof Set)
{ // > compactSize
Set set = (Set) val;
return set.contains(item);
}
// empty
return false;
}
@SuppressWarnings("unchecked")
public Iterator iterator()
{
return new Iterator()
{
final Iterator iter = getCopy().iterator();
E currentEntry = (E) NO_ENTRY;
public boolean hasNext() { return iter.hasNext(); }
public E next()
{
currentEntry = iter.next();
return currentEntry;
}
public void remove()
{
if (currentEntry == NO_ENTRY)
{ // remove() called on iterator
throw new IllegalStateException("remove() called on an Iterator before calling next()");
}
CompactSet.this.remove(currentEntry);
currentEntry = (E)NO_ENTRY;
}
};
}
@SuppressWarnings("unchecked")
private Set getCopy()
{
Set copy = getNewSet(size()); // Use their Set (TreeSet, HashSet, LinkedHashSet, etc.)
if (val instanceof Object[])
{ // 1 to compactSize - copy Object[] into Set
Object[] entries = (Object[]) CompactSet.this.val;
for (Object entry : entries)
{
copy.add((E) entry);
}
}
else if (val instanceof Set)
{ // > compactSize - addAll to copy
copy.addAll((Set)CompactSet.this.val);
}
// else
// { // empty - nothing to copy
// }
return copy;
}
@SuppressWarnings("unchecked")
public boolean add(E item)
{
if (val instanceof Object[])
{ // 1 to compactSize
if (contains(item))
{
return false;
}
Object[] entries = (Object[]) val;
if (size() < compactSize())
{ // Grow array
Object[] expand = new Object[entries.length + 1];
System.arraycopy(entries, 0, expand, 0, entries.length);
// Place new entry at end
expand[expand.length - 1] = item;
val = expand;
}
else
{ // Switch to Map - copy entries
Set set = getNewSet(size() + 1);
entries = (Object[]) val;
for (Object anItem : entries)
{
set.add((E) anItem);
}
// Place new entry
set.add(item);
val = set;
}
return true;
}
else if (val instanceof Set)
{ // > compactSize
Set set = (Set) val;
return set.add(item);
}
// empty
val = new Object[] { item };
return true;
}
@SuppressWarnings("unchecked")
public boolean remove(Object item)
{
if (val instanceof Object[])
{
Object[] local = (Object[]) val;
final int len = local.length;
for (int i=0; i < len; i++)
{
if (compareItems(local[i], item))
{
if (len == 1)
{
val = EMPTY_SET;
}
else
{
Object[] newElems = new Object[len - 1];
System.arraycopy(local, i + 1, local, i, len - i - 1);
System.arraycopy(local, 0, newElems, 0, len - 1);
val = newElems;
}
return true;
}
}
return false; // not found
}
else if (val instanceof Set)
{ // > compactSize
Set set = (Set) val;
if (!set.contains(item))
{
return false;
}
boolean removed = set.remove(item);
if (set.size() == compactSize())
{ // Down to compactSize, need to switch to Object[]
Object[] entries = new Object[compactSize()];
Iterator i = set.iterator();
int idx = 0;
while (i.hasNext())
{
entries[idx++] = i.next();
}
val = entries;
}
return removed;
}
// empty
return false;
}
public void clear()
{
val = EMPTY_SET;
}
/**
* @return new empty Set instance to use when size() becomes {@literal >} compactSize().
*/
protected Set getNewSet() { return new HashSet<>(compactSize() + 1); }
@SuppressWarnings("unchecked")
protected Set getNewSet(int size)
{
Set set = getNewSet();
try
{ // Extra step here is to get a Map of the same type as above, with the "size" already established
// which saves the time of growing the internal array dynamically.
Constructor constructor = ReflectionUtils.getConstructor(set.getClass(), Integer.TYPE);
return (Set) constructor.newInstance(size);
}
catch (Exception ignored)
{
return set;
}
}
protected boolean isCaseInsensitive() { return false; }
protected int compactSize() { return 80; }
}
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