content: /*
   * Copyright (c) 1999, 2013, Oracle and/or its affiliates. All rights reserved.
   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   *
   * This code is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 only, as
   * published by the Free Software Foundation.  Oracle designates this
   * particular file as subject to the "Classpath" exception as provided
   * by Oracle in the LICENSE file that accompanied this code.
   *
   * This code is distributed in the hope that it will be useful, but WITHOUT
   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   * version 2 for more details (a copy is included in the LICENSE file that
   * accompanied this code).
   *
   * You should have received a copy of the GNU General Public License version
   * 2 along with this work; if not, write to the Free Software Foundation,
   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   *
   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
   * or visit www.oracle.com if you need additional information or have any
   * questions.
   */
  
  package openjdk.tools.javac.util;
  
  import java.util.AbstractQueue;
  import java.util.Collection;
  import java.util.Iterator;
  import java.util.NoSuchElementException;
  
  /** A class for constructing lists by appending elements. Modelled after
   *  java.lang.StringBuffer.
   *
   *  <p><b>This is NOT part of any supported API.
   *  If you write code that depends on this, you do so at your own risk.
   *  This code and its internal interfaces are subject to change or
   *  deletion without notice.</b>
   */
  public class ListBuffer<A> extends AbstractQueue<A> {
  
      public static <T> ListBuffer<T> of(T x) {
          ListBuffer<T> lb = new ListBuffer<>();
          lb.add(x);
          return lb;
      }
  
      /** The list of elements of this buffer.
       */
      private List<A> elems;
  
      /** A pointer pointing to the last element of 'elems' containing data,
       *  or null if the list is empty.
       */
      private List<A> last;
  
      /** The number of element in this buffer.
       */
      private int count;
  
      /** Has a list been created from this buffer yet?
       */
      private boolean shared;
  
      /** Create a new initially empty list buffer.
       */
      public ListBuffer() {
          clear();
      }
  
      public final void clear() {
          this.elems = List.nil();
          this.last = null;
          count = 0;
          shared = false;
      }
  
      /** Return the number of elements in this buffer.
       */
      public int length() {
          return count;
      }
      public int size() {
          return count;
      }
  
      /** Is buffer empty?
       */
      public boolean isEmpty() {
          return count == 0;
      }
  
      /** Is buffer not empty?
       */
      public boolean nonEmpty() {
          return count != 0;
      }
  
      /** Copy list and sets last.
       */
      private void copy() {
          if (elems.nonEmpty()) {
              List<A> orig = elems;
  
              elems = last = List.of(orig.head);
  
              while ((orig = orig.tail).nonEmpty()) {
                  last.tail = List.of(orig.head);
                  last = last.tail;
              }
          }
      }
  
      /** Prepend an element to buffer.
       */
      public ListBuffer<A> prepend(A x) {
          elems = elems.prepend(x);
          if (last == null) last = elems;
          count++;
          return this;
      }
  
      /** Append an element to buffer.
       */
      public ListBuffer<A> append(A x) {
          Assert.checkNonNull(x);
          if (shared) copy();
          List<A> newLast = List.of(x);
          if (last != null) {
              last.tail = newLast;
              last = newLast;
          } else {
              elems = last = newLast;
          }
          count++;
          return this;
      }
  
      /** Append all elements in a list to buffer.
       */
      public ListBuffer<A> appendList(List<A> xs) {
          while (xs.nonEmpty()) {
              append(xs.head);
              xs = xs.tail;
          }
          return this;
      }
  
      /** Append all elements in a list to buffer.
       */
      public ListBuffer<A> appendList(ListBuffer<A> xs) {
          return appendList(xs.toList());
      }
  
      /** Append all elements in an array to buffer.
       */
      public ListBuffer<A> appendArray(A[] xs) {
          for (A x : xs) {
              append(x);
          }
          return this;
      }
  
      /** Convert buffer to a list of all its elements.
       */
      public List<A> toList() {
          shared = true;
          return elems;
      }
  
      /** Does the list contain the specified element?
       */
      public boolean contains(Object x) {
          return elems.contains(x);
      }
  
      /** Convert buffer to an array
       */
      public <T> T[] toArray(T[] vec) {
          return elems.toArray(vec);
      }
      public Object[] toArray() {
          return toArray(new Object[size()]);
      }
  
      /** The first element in this buffer.
       */
      public A first() {
          return elems.head;
      }
  
      /** Return first element in this buffer and remove
       */
      public A next() {
          A x = elems.head;
          if (!elems.isEmpty()) {
              elems = elems.tail;
              if (elems.isEmpty()) last = null;
              count--;
          }
          return x;
      }
  
      /** An enumeration of all elements in this buffer.
       */
      public Iterator<A> iterator() {
          return new Iterator<A>() {
              List<A> elems = ListBuffer.this.elems;
              public boolean hasNext() {
                  return !elems.isEmpty();
              }
              public A next() {
                  if (elems.isEmpty())
                      throw new NoSuchElementException();
                  A elem = elems.head;
                  elems = elems.tail;
                  return elem;
              }
              public void remove() {
                  throw new UnsupportedOperationException();
              }
          };
      }
  
      public boolean add(A a) {
          append(a);
          return true;
      }
  
      public boolean remove(Object o) {
          throw new UnsupportedOperationException();
      }
  
      public boolean containsAll(Collection<?> c) {
          for (Object x: c) {
              if (!contains(x))
                  return false;
          }
          return true;
      }
  
      public boolean addAll(Collection<? extends A> c) {
          for (A a: c)
              append(a);
          return true;
      }
  
      public boolean removeAll(Collection<?> c) {
          throw new UnsupportedOperationException();
      }
  
      public boolean retainAll(Collection<?> c) {
          throw new UnsupportedOperationException();
      }
  
      public boolean offer(A a) {
          append(a);
          return true;
      }
  
      public A poll() {
          return next();
      }
  
      public A peek() {
          return first();
      }
  
      public A last() {
          return last != null ? last.head : null;
      }
  }
  