We would like to know how to create elements List backed by array.
/*//w ww . j a va2 s .c o m * This file is a part of Alchemy OS project. * Copyright (C) 2011-2013, Sergey Basalaev <sbasalaev@gmail.com> * * This program is free software: you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation, either version 3 of the License, or * (at your option) any later version. * * This program 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 for more details. * * You should have received a copy of the GNU General Public License * along with this program. If not, see <http://www.gnu.org/licenses/>. */ package alchemy.util; /** * List of elements backed by array. * <p> * Unlike <code>Vector</code> this class is not synchronized. * * @author Sergey Basalaev */ public final class ArrayList { private Object[] elements; private int size; /** Creates new empty ArrayList with default capacity. */ public ArrayList() { this(16); } /** Creates new empty ArrayList with given capacity. */ public ArrayList(int capacity) { elements = new Object[capacity]; size = 0; } private void growBy(int count) { int minCapacity = elements.length + count; int newCapacity = (elements.length * 3) / 2 + 1; if (newCapacity < minCapacity) newCapacity = minCapacity; Object[] data = new Object[newCapacity]; System.arraycopy(elements, 0, data, 0, size); elements = data; } /** Returns number of elements in this list. */ public int size() { return size; } /** Returns true if this list contains no elements. */ public boolean isEmpty() { return size == 0; } /** Removes all elements from this list. */ public void clear() { for (int i=size-1; i>=0; i--) { elements[i] = null; } size = 0; } /** Returns element at given index. */ public Object get(int index) { if (index < 0 || index >= size) throw new IndexOutOfBoundsException(); return elements[index]; } /** Returns first element of this list. */ public Object first() { if (size == 0) throw new IndexOutOfBoundsException(); return elements[0]; } /** Returns last element of this list. */ public Object last() { if (size == 0) throw new IndexOutOfBoundsException(); return elements[size-1]; } /** Sets new value to the elements of this list. */ public void set(int index, Object e) { if (index < 0 || index >= size) throw new IndexOutOfBoundsException(); elements[index] = e; } /** Inserts element in given position of the list. */ public void insert(int index, Object e) { if (index < 0 || index > size) throw new IndexOutOfBoundsException(); if (elements.length == size) growBy(1); if (index < size) System.arraycopy(elements, index, elements, index+1, size-index); elements[index] = e; size++; } /** Inserts elements from given array. */ public void insertFrom(int index, Object array, int ofs, int len) { if (len < 0) len = Arrays.arrayLength(array); if (len == 0) return; if (elements.length < size + len) growBy(len); if (index < size) System.arraycopy(elements, index, elements, index+len, size-index); Arrays.arrayCopy(array, ofs, elements, index, len); size += len; } /** Adds element to the end of the list. */ public void add(Object e) { if (elements.length == size) growBy(1); elements[size] = e; size++; } /** Adds elements from given array. */ public void addFrom(Object array, int ofs, int len) { if (len < 0) len = Arrays.arrayLength(array); if (len == 0) return; if (elements.length < size + len) growBy(len); Arrays.arrayCopy(array, ofs, elements, size, len); size += len; } /** Removes element from given position of the list. */ public void remove(int index) { if (index < 0) index += size; if (index < 0 || index >= size) throw new IndexOutOfBoundsException(); size--; if (index < size) System.arraycopy(elements, index+1, elements, index, size-index); elements[size] = null; } /** Finds and removes given element. */ public boolean remove(Object e) { int idx = indexOf(e, 0); if (idx >= 0) remove(idx); return idx >= 0; } /** Returns sublist of this list. */ public ArrayList getRange(int from, int to) { if (from < 0) from += size; if (to < 0) to += size; int len = to-from; ArrayList list = new ArrayList(len); list.size = len; System.arraycopy(elements, from, list.elements, 0, len); return list; } /** Tests whether list contains given element. */ public boolean contains(Object e) { return indexOf(e, 0) >= 0; } /** * Returns index of the first occurence of given object * after given index. * Returns -1 if the list does not contain it. */ public int indexOf(Object e, int from) { for (int index = from; index < size; index++) { if (e == null ? elements[index] == null : e.equals(elements[index])) { return index; } } return -1; } /** * Returns index of the first occurence of given object. * Returns -1 if the list does not contain it. */ public int indexOf(Object e) { return indexOf(e, 0); } /** * Returns index of the last occurence of given object. * Returns -1 if the list does not contain it. */ public int lastIndexOf(Object e) { for (int index = size-1; index >= 0; index--) { if (e == null ? elements[index] == null : e.equals(elements[index])) { return index; } } return -1; } /** * Copies portion of this list into given array. * * @param from index of the first element to copy * @param array object or promitive array to copy into * @param offset offset in array to place first element * @param len number of elements to copy */ public void copyInto(int from, Object array, int offset, int len) { if (len < 0) len = Arrays.arrayLength(array); if (len == 0) return; if (from < 0 || from >= size || len > size || offset < 0 || offset + len > Arrays.arrayLength(array)) throw new IndexOutOfBoundsException(); Arrays.arrayCopy(elements, from, array, offset, len); } /** Copies contents of this list into given array. */ public void copyInto(Object array) { copyInto(0, array, 0, size); } void buildString(ArrayList dejaVu, StringBuffer buf) { if (dejaVu.indexOf(this, 0) >= 0) { buf.append("[...]"); } else { dejaVu.add(this); buf.append('['); for (int i=0; i<size; i++) { if (i != 0) buf.append(", "); Strings.buildString(elements[i], dejaVu, buf); } buf.append(']'); dejaVu.remove(this); } } /** Returns string representation of this list. */ public String toString() { StringBuffer buf = new StringBuffer(); buildString(new ArrayList(), buf); return buf.toString(); } }