Java中AyyarList类的基本实现

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ArrayList：底层用数组实现，线程不安全，效率高。所以，查询快，插入、删除慢。一般用AyyayList就够了。

LinkedList：基于链表实现，线程不安全，效率高。所以，查询慢，插入、删除快。

Vector：基于数组实现。线程安全的，效率低。只有在多线程情况时才是用Vector。

/** * 自己实现一个ArrayList，帮助我们更好地理解ArrayList类的底层结构 * @author Administrator * */public class MyArrayList {private Object[] elementData;private int size;public MyArrayList(){this(10); //默认的数组长度为10}public MyArrayList(int initialCapacity){if(initialCapacity<0)try {throw new Exception();} catch (Exception e) {// TODO Auto-generated catch blocke.printStackTrace();}elementData = new Object[initialCapacity];}public int size(){return size;}public void ensureCapacity(){//若数组已满，则给数组扩容if(size==elementData.length){Object[] newArray = new Object[size*2];System.arraycopy(elementData, 0, newArray, 0, elementData.length);elementData = newArray;}}public void add(Object o){ensureCapacity();elementData[size]=o;size++;}public void add(int index, Object obj){rangeCheck(index);ensureCapacity();for(int i=size-1;i>=index;i--){elementData[i+1]=elementData[i];}elementData[index]=obj;size++;}public boolean isEmpty(){return size==0;}public Object get(int index){rangeCheck(index);return elementData[index];}public Object remove(int index){rangeCheck(index);Object deletedObject = elementData[index];//int numMoved = size-index-1;//System.arraycopy(elementData, index+1, elementData, index, numMoved);for(int i=index+1; i<this.size();i++){elementData[i-1]=elementData[i];}elementData[--size]=null;return deletedObject;}public boolean remove(Object obj){for(int i=0; i<this.size();i++){if(elementData[i].equals(obj)){remove(i);return true;}}return false;}public Object set(int index, Object obj){rangeCheck(index);Object oldValue=elementData[index];elementData[index]=obj;return oldValue;}private void rangeCheck(int index){if( index < 0 ||index >= size){try {throw new Exception();} catch (Exception e) {// TODO Auto-generated catch blocke.printStackTrace();}}}public static void main(String[] args) {// TODO Auto-generated method stubMyArrayList list = new MyArrayList(3);list.add(123);list.add("haha");list.add("wxxyy");list.add("you");System.out.println(list.get(3));}}

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