org.apache.openejb.util.LinkedListStack Maven / Gradle / Ivy
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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.apache.openejb.util;
public class LinkedListStack implements Stack {
private LinkedEntry occupiedEntries;
private LinkedEntry vacantEntries;
private int size;
public LinkedListStack(int initialSize) {
for (int i = 0; i < initialSize; i++)
vacantEntries = new LinkedEntry(null, vacantEntries);
}
public synchronized Object push(Object object) {
/* Take an entry from the vacant list and move it to the occupied list. */
if (vacantEntries == null)
occupiedEntries = new LinkedEntry(object, occupiedEntries);
else {
LinkedEntry entry = vacantEntries;
vacantEntries = vacantEntries.next;
occupiedEntries = entry.set(object, occupiedEntries);
}
++size;
return object;
}
public synchronized Object pop() throws java.util.EmptyStackException {
/* Take an entry from the occupied list and move it to the vacant list. */
LinkedEntry entry = occupiedEntries;
if (entry == null) return null;
occupiedEntries = occupiedEntries.next;
Object value = entry.value;
vacantEntries = entry.set(null, vacantEntries);
--size;
return value;
}
public synchronized int size() {
return size;
}
static class LinkedEntry {
LinkedEntry next;
Object value;
LinkedEntry(Object value, LinkedEntry next) {
set(value, next);
}
LinkedEntry set(Object value, LinkedEntry next) {
this.next = next;
this.value = value;
return this;
}
}
}