org.glassfish.pfl.basic.contain.StackImpl Maven / Gradle / Ivy
/*
* Copyright (c) 1997, 2018 Oracle and/or its affiliates. All rights reserved.
*
* This program and the accompanying materials are made available under the
* terms of the Eclipse Distribution License v. 1.0, which is available at
* http://www.eclipse.org/org/documents/edl-v10.php.
*
* SPDX-License-Identifier: BSD-3-Clause
*/
package org.glassfish.pfl.basic.contain ;
import java.util.EmptyStackException ;
// We implement a Stack here instead of using java.util.Stack because
// java.util.Stack is thread-safe, negatively impacting performance.
// We use an ArrayList instead since it is not thread-safe.
// RequestInfoStack is used quite frequently.
public class StackImpl {
// The stack for RequestInfo objects.
private Object[] data = new Object[3] ;
private int top = -1 ;
// Tests if this stack is empty.
public final boolean empty() {
return top == -1;
}
// Looks at the object at the top of this stack without removing it
// from the stack.
@SuppressWarnings("unchecked")
public final E peek() {
if (empty()) {
throw new EmptyStackException();
}
return (E)data[ top ];
}
// Removes the object at the top of this stack and returns that
// object as the value of this function.
@SuppressWarnings("unchecked")
public final E pop() {
Object obj = peek() ;
data[top] = null ;
top-- ;
return (E)obj;
}
private void ensure()
{
if (top == (data.length-1)) {
int newSize = 2*data.length ;
Object[] newData = new Object[ newSize ] ;
System.arraycopy( data, 0, newData, 0, data.length ) ;
data = newData ;
}
}
// Pushes an item onto the top of the stack
public final Object push( E item ) {
ensure() ;
top++ ;
data[top] = item;
return item;
}
}