Java ArrayList的底层实现

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package com.soto.collection;/** * 自己实现一个ArrayList,帮助我们更好地理解ArrayList的底层结构; * @author 王 * */public class SxtArrayList {private Object[] elementData;private int size;public int size(){return size;}public boolean isEmpty(){return size == 0;}public  SxtArrayList(){this(10);}public SxtArrayList(int initialCapacity){if(initialCapacity<0){try {throw new Exception();} catch (Exception e) {e.printStackTrace();}}elementData = new Object[initialCapacity];  //初始化 容量为10 }public void add(Object obj){elementData[size++] = obj;   //若超过容量了，那么..数组扩容if(size==elementData.length){//实质：搞个新数组Object[] newarray = new Object[size*2+1];//数组的copy:System.arraycopy(elementData, 0, newarray, 0, elementData.length);elementData = newarray;}}public Object get(int index){rangeCheck(index);return elementData[index];}public void remove(int index){  rangeCheck(index); //删除指定位置对象，删除某位置，相当于 将后往前挪:int numMoved = size-index-1;if(numMoved>0){System.arraycopy(elementData, index+1, elementData, index, numMoved);}}public void remove(Object obj){for(int i=0;i<size;i++){if(get(i).equals(obj)){   //注意底层调用的equals方法而不是==。remove(i);}}}private void rangeCheck(int index){if(index<0||index>size){try {throw new Exception();} catch (Exception e) {e.printStackTrace();}}}public Object set(int index, Object obj){rangeCheck(index);        Object oldValue = elementData[index];        elementData[index] = obj;        return oldValue;}public void add(int index, Object obj){rangeCheck(index);ensureCapacity(); //扩容System.arraycopy(elementData, index, elementData, index + 1,                size - index);elementData[index] = obj;size++;}private void ensureCapacity(){//扩容if(size==elementData.length){//实质：搞个新数组Object[] newarray = new Object[size*2+1];//数组的copy:System.arraycopy(elementData, 0, newarray, 0, elementData.length);elementData = newarray;}}public static void main(String[] args) {SxtArrayList list = new SxtArrayList(3);list.add("222");list.add("333");list.add("444");list.add("555");list.add("666");list.add("777");System.out.println(list.size());System.out.println(list.get(6));}}
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