ArrayList增、删、改方法实现

  1 //ArrayList增、删、查代码具体实现
  2
  3 package com.coding.basic;
  4
  5 import java.util.Arrays;
  6
  7 public class MyArrayList implements List {
  8
  9     private static final int DEFAULT_CAPACITY = 10;
 10     private int size = 0;
 11
 12     Object[] elementData;
 13
 14     // 默认数组容量是10
 15     public MyArrayList() {
 16         this(DEFAULT_CAPACITY);
 17     }
 18
 19     // 传入数组容量
 20     public MyArrayList(int capacity) {
 21
 22         if (capacity < 0) {
 23
 24             throw new IllegalArgumentException("Illegal Capacity: " + capacity);
 25         }
 26         if (capacity >= 0) {
 27             elementData = new Object[capacity];
 28             size = elementData.length;
 29         }
 30     }
 31
 32     // 保证数组容量
 33     private void ensurecapacity(int mincapacity) {
 34
 35         int oldcapacity = elementData.length;
 36         if (mincapacity > oldcapacity) {
 37             Object olddata[] = elementData;
 38             // 1.5倍括容是最好的倍數
 39             int newcapacity = oldcapacity * 3 / 2;
 40
 41             if (mincapacity > newcapacity) {
 42                 newcapacity = mincapacity;
 43             }
 44             elementData = Arrays.copyOf(elementData, newcapacity);
 45         }
 46
 47     }
 48
 49     // 在尾部添加元素
 50     public void add(Object o) {
 51         ensurecapacity(size + 1);
 52         elementData[size++] = o;
 53
 54     }
 55
 56     // 在任意位置添加元素
 57     public void add(int index, Object o) {
 58         RangeCheck(index);
 59         ensurecapacity(size + 1);
 60         for (int x = size - 1; x > index; x--) {
 61             elementData[x + 1] = elementData[x];
 62
 63         }
 64         elementData[index + 1] = o;
 65     }
 66
 67     // 获取任意位置上的元素
 68     public Object get(int index) {
 69         RangeCheck(index);
 70
 71         return elementData[index];
 72
 73     }
 74
 75     // 检查索引值范围
 76     private void RangeCheck(int index) {
 77         if (index < 0 || index >= size) {
 78             throw new IndexOutOfBoundsException("Index: " + index + ", Size: " + size);
 79         }
 80
 81     }
 82
 83     // 删除任意位置元素并返回该元素
 84     public Object remove(int index) {
 85         return remove(index, elementData);
 86     }
 87
 88     // 删除任意位置元素并返回该元素
 89     public Object remove(int index, Object[] elementData) {
 90         RangeCheck(index);
 91         if (index >= 0 && index < size - 1) {
 92             for (int i = index; i < size - 1; i++) {
 93                 elementData[i] = elementData[i + 1];
 94
 95             }
 96
 97         }
 98         if (index == size - 1) {
 99             elementData[index] = elementData[size - 1];
100         }
101
102         size--;
103         return elementData[index];
104     }
105
106     // 获取数组长度
107     public int size() {
108         return size;
109     }
110
111 }