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| 1 | +package cn.fyl.first; |
| 2 | + |
| 3 | +/* |
| 4 | + * 动态数组 |
| 5 | + */ |
| 6 | +public class ArrayList implements List { |
| 7 | + |
| 8 | + // 记录数组大小 |
| 9 | + private int size = 0; |
| 10 | + |
| 11 | + // 设数组容量为3 |
| 12 | + private Object[] elementData = new Object[3]; |
| 13 | + |
| 14 | + // 扩容 |
| 15 | + public void dilatation(int newCapacity) { |
| 16 | + |
| 17 | + if (newCapacity < size) { |
| 18 | + return; |
| 19 | + } |
| 20 | + |
| 21 | + Object[] old = elementData; |
| 22 | + elementData = new Object[newCapacity]; |
| 23 | + for (int i = 0; i < size; i++) { |
| 24 | + elementData[i] = old[i]; |
| 25 | + } |
| 26 | + |
| 27 | + } |
| 28 | + |
| 29 | + // 插入值 |
| 30 | + public void add(Object o) { |
| 31 | + add(size(), o); |
| 32 | + } |
| 33 | + |
| 34 | + // 按索引插入值 |
| 35 | + public void add(int index, Object o) { |
| 36 | + if (elementData.length == size()) { |
| 37 | + dilatation(size() * 2 + 1); |
| 38 | + } |
| 39 | + // 插入的位置小于数组大小，将index位置的值依次向后退一位 |
| 40 | + for (int i = size; i > index; i--) { |
| 41 | + elementData[i] = elementData[i - 1]; |
| 42 | + } |
| 43 | + elementData[index] = o; |
| 44 | + size++; |
| 45 | + |
| 46 | + } |
| 47 | + |
| 48 | + // 取值 |
| 49 | + public Object get(int index) { |
| 50 | + |
| 51 | + if (index > size) { |
| 52 | + return null; |
| 53 | + } else { |
| 54 | + return elementData[index]; |
| 55 | + } |
| 56 | + |
| 57 | + } |
| 58 | + |
| 59 | + // 按索引删除该值 |
| 60 | + public Object remove(int index) { |
| 61 | + Object o = elementData[index]; |
| 62 | + // 删除的位置小于数组大小，将index位置后面的值依次向前挪一位 |
| 63 | + for (int i = index; i < elementData.length - 1; i++) { |
| 64 | + elementData[i] = elementData[i + 1]; |
| 65 | + } |
| 66 | + size--; |
| 67 | + return o; |
| 68 | + } |
| 69 | + |
| 70 | + // 返回数组大小 |
| 71 | + public int size() { |
| 72 | + return size; |
| 73 | + } |
| 74 | + |
| 75 | + //迭代器 |
| 76 | + class MyIterator implements Iterator { |
| 77 | + int current = 0; |
| 78 | + |
| 79 | + public boolean hasNext() { |
| 80 | + return current < size; |
| 81 | + } |
| 82 | + |
| 83 | + public Object next() { |
| 84 | + if (hasNext()) |
| 85 | + return elementData[current++]; |
| 86 | + else |
| 87 | + throw new java.util.NoSuchElementException(); |
| 88 | + } |
| 89 | + |
| 90 | + } |
| 91 | + |
| 92 | + public static void main(String[] args) { |
| 93 | + ArrayList a = new ArrayList(); |
| 94 | + a.add(0, 1); |
| 95 | + a.add(2); |
| 96 | + a.add(3); |
| 97 | + a.add(4); |
| 98 | + a.add(1, 0); |
| 99 | + a.remove(3); |
| 100 | + ArrayList.MyIterator m = a.new MyIterator(); |
| 101 | + System.err.println(a.elementData.length); |
| 102 | + while(m.hasNext()){ |
| 103 | + System.out.print(m.next()+" "); |
| 104 | + } |
| 105 | + } |
| 106 | + |
| 107 | +} |
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