org.ttzero.excel.reader.FixSizeLRUCache Maven / Gradle / Ivy
/*
* Copyright (c) 2017-2018, [email protected] All Rights Reserved.
*
* 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
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* 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.
*/
package org.ttzero.excel.reader;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.function.Consumer;
/**
* Implemented by the LRU page elimination algorithm.
* The time complexity of the push, get, and remove is O(1).
*
* @author guanquan.wang at 2018-10-31 16:06
*/
public class FixSizeLRUCache implements Cache {
protected static class E implements Cache.Entry {
private final K k;
private V v;
private E(K k, V v) {
this.k = k;
this.v = v;
}
@Override
public K getKey() {
return k;
}
@Override
public V getValue() {
return v;
}
@Override
public String toString() {
return k + ":" + v;
}
}
private static class Node {
private final V data;
private Node prev, next;
private Node(V data, Node prev, Node next) {
this.data = data;
this.prev = prev;
this.next = next;
}
}
/**
* Double linked
*/
private Node> first, last;
/**
* The elements limit
*/
private final int limit;
private final Map>> table;
public static FixSizeLRUCache create() {
return new FixSizeLRUCache<>();
}
public static FixSizeLRUCache create(int size) {
return new FixSizeLRUCache<>(size);
}
/**
* Create a fix size cache witch size is {@code 512}
*/
private FixSizeLRUCache() {
this(1 << 9);
}
private FixSizeLRUCache(int limit) {
this.limit = limit;
// Create double limit size
table = new HashMap<>(limit);
}
/**
* Returns the value to which the specified key is mapped,
* or {@code null} if this cache contains no mapping for the key.
*
* @param k the key whose associated value is to be returned
* @return the value to which the specified key is mapped, or
* {@code null} if this cache contains no mapping for the key
*/
@Override
public V get(K k) {
final Node> o = getNode(k);
return o != null ? o.data.v : null;
}
/**
* Associates the specified value with the specified key in this cache.
* If the cache previously contained a mapping for
* the key, the old value is replaced by the specified value.
*
* @param k key with which the specified value is to be associated
* the key must not be null
* @param v value to be associated with the specified key
*/
@Override
public void put(K k, V v) {
final Node> o = getNode(k);
// Insert at header if not found
if (o == null) {
final Node> f = first;
final Node> newNode = new Node<>(new E<>(k, v), null, f);
first = newNode;
if (f == null) last = newNode;
else f.prev = newNode;
table.put(k, newNode);
if (table.size() > limit) remove();
}
// Replace the old value
else {
o.data.v = v;
}
}
/**
* Removes the mapping for a key from this cache if it is present
* (optional operation). More formally, if this cache contains a mapping
* from key k to value v, that mapping
* is removed.
*
* @param k key whose mapping is to be removed from the cache
* @return the previous value associated with key, or
* null if there was no mapping for key.
*/
@Override
public V remove(K k) {
final Node> o = table.get(k);
// Not found
if (o == null) return null;
// Remove the keyword from the hash table to make them unsearchable
table.remove(k);
if (table.isEmpty()) {
clear();
return o.data.v;
}
final Node> prev = o.prev, next = o.next;
// The first node
if (prev == null) {
first = next;
} else {
prev.next = next;
o.prev = null;
}
// The last node
if (next == null) {
last = prev;
} else {
next.prev = prev;
o.next = null;
}
return o.data.v;
}
/**
* Remove the last item
*
* @return the last item
*/
protected E remove() {
final Node> l = last;
if (l == null) {
return null;
}
final E data = l.data;
last = last.prev;
if (last != null) {
last.next = null;
}
table.remove(data.k);
if (last == null) first = null;
return data;
}
/**
* Removes all the mappings from this cache (optional operation).
* The cache will be empty after this call returns.
*/
@Override
public void clear() {
first = null;
last = null;
table.clear();
}
/**
* Returns the number of key-value mappings in this cache.
*
* @return the number of key-value mappings in this cache
*/
@Override
public int size() {
return table.size();
}
/**
* An inner iterator
*/
private class CacheIterator implements Iterator> {
private Node> first;
private CacheIterator(Node> first) {
this.first = first;
}
@Override
public boolean hasNext() {
return first != null;
}
@Override
public E next() {
E e = first.data;
first = first.next;
return e;
}
}
/**
* Returns an iterator over elements of type {@code Cache.Entry}.
*
* @return an Iterator.
*/
@Override
public Iterator> iterator() {
return new CacheIterator(first);
}
/**
* Performs the given action for each element of the {@code Iterable}
* until all elements have been processed or the action throws an
* exception. Unless otherwise specified by the implementing class,
* actions are performed in the order of iteration (if an iteration order
* is specified). Exceptions thrown by the action are relayed to the
* caller.
*
* The default implementation behaves as if:
*
{@code
* for (T t : this)
* action.accept(t);
* }
*
* @param action The action to be performed for each element
* @throws NullPointerException if the specified action is null
*/
@Override
public void forEach(Consumer> action) {
Node> f = first;
for (; f != null; f = f.next) {
action.accept(f.data);
}
}
/**
* Find and move to head
*
* @param k key
* @return null if not found
*/
Node> getNode(K k) {
final Node> o = table.get(k);
// Not found
if (o == null) return null;
// Move node to head
if (o != first) {
if (o.next != null) {
o.prev.next = o.next;
o.next.prev = o.prev;
} else {
o.prev.next = null;
last = o.prev;
}
first.prev = o;
o.next = first;
o.prev = null;
first = o;
}
return o;
}
@Override
public String toString() {
Node> f = first;
if (f != null) {
StringBuilder buf = new StringBuilder();
buf.append(f.data.k).append(':').append(f.data.v);
f = f.next;
for (int i = 1, n = 1000; i < n && f != null; f = f.next, i++) {
buf.append("=>").append(f.data.k).append(':').append(f.data.v);
}
return buf.toString();
} else return "";
}
}
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