写在前面的话：读书破万卷，编码如有神
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下文主要对java.util.ArrayList<E>中的Iterator和List操作进行介绍，主要内容包括:
1、ArrayList的Iterator和ListIterator操作
2、ArrayList的subList操作
参考内容：
1、JDK源码(1.7)
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1. ArrayList的Iterator和List操作
Iterator和子List操作
关于Iterator操作这里涉及到"迭代器模式",可以简单看看
(1)Iterator<E> iterator()
功能: 返回列表的Iterator实例
示例代码:
1 import java.util.ArrayList; 2 import java.util.Iterator; 3 4 public class ArrayListTest { 5 public static void main(String[] args) { 6 ArrayList<Integer> list = new ArrayList<Integer>(); 7 list.add(22); 8 list.add(33); 9 list.add(44); 10 list.add(11); 11 list.add(15); 12 list.add(12); 13 list.add(7); 14 list.add(3); 15 System.out.println("list1 :" + list); 16 //测试ArrayList的'Iterator<E> iterator()'方法的使用 17 Iterator<Integer> it = list.iterator(); 18 while(it.hasNext()){ 19 System.out.print(it.next() +" "); 20 } 21 System.out.println(""); 22 System.out.println("list2 :" + list); 23 it.remove(); 24 System.out.println("list3 :" + list); 25 } 26 } 27 28 运行结果: 29 list1 :[22, 33, 44, 11, 15, 12, 7, 3] 30 22 33 44 11 15 12 7 3 31 list2 :[22, 33, 44, 11, 15, 12, 7, 3] 32 list3 :[22, 33, 44, 11, 15, 12, 7]
源代码如下:（这个方法直接用了一个内部类来帮助实现功能）
1 public Iterator<E> iterator() { 2 //每次调用iterator()方法都会去new一个Itr类 3 return new Itr(); 4 }
1 private class Itr implements Iterator<E> { 2 //下一个返回元素的索引 3 int cursor; // index of next element to return 4 //最近返回元素的索引 5 int lastRet = -1; // index of last element returned; -1 if no such 6 //fast-fail标记标识 7 int expectedModCount = modCount; 8 9 //如果列表仍有元素可以迭代,则返回true 10 public boolean hasNext() { 11 return cursor != size; 12 } 13 14 //返回迭代的下一个元素 15 @SuppressWarnings("unchecked") 16 public E next() { 17 //检查fast-fail机制 18 checkForComodification(); 19 int i = cursor; 20 if (i >= size) 21 throw new NoSuchElementException(); 22 Object[] elementData = ArrayList.this.elementData; 23 if (i >= elementData.length) 24 throw new ConcurrentModificationException(); 25 cursor = i + 1; 26 return (E) elementData[lastRet = i]; 27 } 28 //从迭代器指向的列表中移除迭代器返回的最后一个元素 29 public void remove() { 30 //检查迭代器是否返回过元素 31 if (lastRet < 0) 32 throw new IllegalStateException(); 33 //检查fast-fail机制 34 checkForComodification(); 35 36 try { 37 //删除列表中最后返回的那个元素 38 ArrayList.this.remove(lastRet); 39 cursor = lastRet; 40 lastRet = -1; 41 expectedModCount = modCount; 42 } catch (IndexOutOfBoundsException ex) { 43 throw new ConcurrentModificationException(); 44 } 45 } 46 47 //检查fast-fail机制标识 48 final void checkForComodification() { 49 if (modCount != expectedModCount) 50 throw new ConcurrentModificationException(); 51 } 52 }
(2)ListIterator<E> listIterator()
功能: 返回列表的ListIterator实例
源代码如下:（这个方法直接用了一个内部类来帮助实现功能）
1 public ListIterator<E> listIterator() { 2 return new ListItr(0); 3 }
(3)ListIterator<E> listIterator(int index)
功能: 返回列表的ListIterator实例
源代码如下:（这个方法直接用了一个内部类来帮助实现功能）
1 public ListIterator<E> listIterator(int index) { 2 //首先检查index是否合法,如果不合法则抛出异常 3 if (index < 0 || index > size) 4 throw new IndexOutOfBoundsException("Index: "+index); 5 //创建一个ListItr对象 6 return new ListItr(index); 7 }
1 private class ListItr extends Itr implements ListIterator<E> { 2 /*带参数构造函数*/ 3 ListItr(int index) { 4 super(); 5 cursor = index; 6 } 7 //如果以逆向遍历列表,列表迭代器有多个元素,则返回true 8 public boolean hasPrevious() { 9 return cursor != 0; 10 } 11 //返回对next的后续调用所返回的元素的索引 12 public int nextIndex() { 13 return cursor; 14 } 15 //返回对previous的后续调用所返回元素的索引 16 public int previousIndex() { 17 return cursor - 1; 18 } 19 //返回列表中前一个元素 20 @SuppressWarnings("unchecked") 21 public E previous() { 22 //检查fast-fail机制标识 23 checkForComodification(); 24 //返回索引下标值减1 25 int i = cursor - 1; 26 if (i < 0) 27 throw new NoSuchElementException(); 28 Object[] elementData = ArrayList.this.elementData; 29 if (i >= elementData.length) 30 throw new ConcurrentModificationException(); 31 cursor = i; 32 //返回元素 33 return (E) elementData[lastRet = i]; 34 } 35 //用指定元素替换next或者previous返回的最后一个元素 36 public void set(E e) { 37 if (lastRet < 0) 38 throw new IllegalStateException(); 39 //检查fast-fail机制 40 checkForComodification(); 41 42 try { 43 ArrayList.this.set(lastRet, e); 44 } catch (IndexOutOfBoundsException ex) { 45 throw new ConcurrentModificationException(); 46 } 47 } 48 //将指定的元素插入列表 49 public void add(E e) { 50 //检查fast-fail机制 51 checkForComodification(); 52 53 try { 54 int i = cursor; 55 //添加元素e到计划中 56 ArrayList.this.add(i, e); 57 cursor = i + 1; 58 lastRet = -1; 59 expectedModCount = modCount; 60 } catch (IndexOutOfBoundsException ex) { 61 throw new ConcurrentModificationException(); 62 } 63 } 64 }
(4)List<E> subList(int fromIndex, int toIndex)
功能: 返回列表从索引位置fromIndex到toIndex之间元素组成的子列表
源代码如下:
1 public List<E> subList(int fromIndex, int toIndex) { 2 //检查参数fromIndex和toIndex是否合法 3 subListRangeCheck(fromIndex, toIndex, size); 4 //创建一个SubList对象 5 return new SubList(this, 0, fromIndex, toIndex); 6 } 7 8 static void subListRangeCheck(int fromIndex, int toIndex, int size) { 9 //起始位置fromIndex小于0，则抛出异常 10 if (fromIndex < 0) 11 throw new IndexOutOfBoundsException("fromIndex = " + fromIndex); 12 //终止位置toIndex大于列表中元素个数size,则抛出异常 13 if (toIndex > size) 14 throw new IndexOutOfBoundsException("toIndex = " + toIndex); 15 //起始位置fromIndex 大于 终止位置toIndex,则抛出异常 16 if (fromIndex > toIndex) 17 throw new IllegalArgumentException("fromIndex(" + fromIndex +") > toIndex(" + toIndex + ")"); 18 } 19 20 /* 21 内部类，为了配合subList方法 22 */ 23 private class SubList extends AbstractList<E> implements RandomAccess { 24 private final AbstractList<E> parent; 25 private final int parentOffset; 26 private final int offset; 27 int size; 28 //构造方法 29 SubList(AbstractList<E> parent, 30 int offset, int fromIndex, int toIndex) { 31 this.parent = parent; 32 this.parentOffset = fromIndex; 33 this.offset = offset + fromIndex; 34 this.size = toIndex - fromIndex; 35 this.modCount = ArrayList.this.modCount; 36 } 37 38 public E set(int index, E e) { 39 rangeCheck(index); 40 checkForComodification(); 41 E oldValue = ArrayList.this.elementData(offset + index); 42 ArrayList.this.elementData[offset + index] = e; 43 return oldValue; 44 } 45 46 public E get(int index) { 47 rangeCheck(index); 48 checkForComodification(); 49 return ArrayList.this.elementData(offset + index); 50 } 51 52 public int size() { 53 checkForComodification(); 54 return this.size; 55 } 56 57 public void add(int index, E e) { 58 rangeCheckForAdd(index); 59 checkForComodification(); 60 parent.add(parentOffset + index, e); 61 this.modCount = parent.modCount; 62 this.size++; 63 } 64 65 public E remove(int index) { 66 rangeCheck(index); 67 checkForComodification(); 68 E result = parent.remove(parentOffset + index); 69 this.modCount = parent.modCount; 70 this.size--; 71 return result; 72 } 73 74 protected void removeRange(int fromIndex, int toIndex) { 75 checkForComodification(); 76 parent.removeRange(parentOffset + fromIndex, 77 parentOffset + toIndex); 78 this.modCount = parent.modCount; 79 this.size -= toIndex - fromIndex; 80 } 81 82 public boolean addAll(Collection<? extends E> c) { 83 return addAll(this.size, c); 84 } 85 86 public boolean addAll(int index, Collection<? extends E> c) { 87 rangeCheckForAdd(index); 88 int cSize = c.size(); 89 if (cSize==0) 90 return false; 91 92 checkForComodification(); 93 parent.addAll(parentOffset + index, c); 94 this.modCount = parent.modCount; 95 this.size += cSize; 96 return true; 97 } 98 99 public Iterator<E> iterator() { 100 return listIterator(); 101 } 102 103 public ListIterator<E> listIterator(final int index) { 104 checkForComodification(); 105 rangeCheckForAdd(index); 106 final int offset = this.offset; 107 108 return new ListIterator<E>() { 109 int cursor = index; 110 int lastRet = -1; 111 int expectedModCount = ArrayList.this.modCount; 112 113 public boolean hasNext() { 114 return cursor != SubList.this.size; 115 } 116 117 @SuppressWarnings("unchecked") 118 public E next() { 119 checkForComodification(); 120 int i = cursor; 121 if (i >= SubList.this.size) 122 throw new NoSuchElementException(); 123 Object[] elementData = ArrayList.this.elementData; 124 if (offset + i >= elementData.length) 125 throw new ConcurrentModificationException(); 126 cursor = i + 1; 127 return (E) elementData[offset + (lastRet = i)]; 128 } 129 130 public boolean hasPrevious() { 131 return cursor != 0; 132 } 133 134 @SuppressWarnings("unchecked") 135 public E previous() { 136 checkForComodification(); 137 int i = cursor - 1; 138 if (i < 0) 139 throw new NoSuchElementException(); 140 Object[] elementData = ArrayList.this.elementData; 141 if (offset + i >= elementData.length) 142 throw new ConcurrentModificationException(); 143 cursor = i; 144 return (E) elementData[offset + (lastRet = i)]; 145 } 146 147 public int nextIndex() { 148 return cursor; 149 } 150 151 public int previousIndex() { 152 return cursor - 1; 153 } 154 155 public void remove() { 156 if (lastRet < 0) 157 throw new IllegalStateException(); 158 checkForComodification(); 159 160 try { 161 SubList.this.remove(lastRet); 162 cursor = lastRet; 163 lastRet = -1; 164 expectedModCount = ArrayList.this.modCount; 165 } catch (IndexOutOfBoundsException ex) { 166 throw new ConcurrentModificationException(); 167 } 168 } 169 170 public void set(E e) { 171 if (lastRet < 0) 172 throw new IllegalStateException(); 173 checkForComodification(); 174 175 try { 176 ArrayList.this.set(offset + lastRet, e); 177 } catch (IndexOutOfBoundsException ex) { 178 throw new ConcurrentModificationException(); 179 } 180 } 181 182 public void add(E e) { 183 checkForComodification(); 184 185 try { 186 int i = cursor; 187 SubList.this.add(i, e); 188 cursor = i + 1; 189 lastRet = -1; 190 expectedModCount = ArrayList.this.modCount; 191 } catch (IndexOutOfBoundsException ex) { 192 throw new ConcurrentModificationException(); 193 } 194 } 195 196 final void checkForComodification() { 197 if (expectedModCount != ArrayList.this.modCount) 198 throw new ConcurrentModificationException(); 199 } 200 }; 201 } 202 203 public List<E> subList(int fromIndex, int toIndex) { 204 subListRangeCheck(fromIndex, toIndex, size); 205 return new SubList(this, offset, fromIndex, toIndex); 206 } 207 208 private void rangeCheck(int index) { 209 if (index < 0 || index >= this.size) 210 throw new IndexOutOfBoundsException(outOfBoundsMsg(index)); 211 } 212 213 private void rangeCheckForAdd(int index) { 214 if (index < 0 || index > this.size) 215 throw new IndexOutOfBoundsException(outOfBoundsMsg(index)); 216 } 217 218 private String outOfBoundsMsg(int index) { 219 return "Index: "+index+", Size: "+this.size; 220 } 221 222 private void checkForComodification() { 223 if (ArrayList.this.modCount != this.modCount) 224 throw new ConcurrentModificationException(); 225 } 226 }
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java.util.ArrayList系列文章
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