实现了增删改查四项基本功能实现了Iterator迭代器实现了数组的动态扩容
package basicKnowledge.集合框架.arrayList;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.function.Consumer;
/**
* @program:summary
* @author:peicc
* @create:2019-07-18 14:34:39
**/
//ArrayList的简单实现
public class MyArrayList<AnyType> implements Iterable<AnyType> {
private Object[] elementData;
private static final int DEFAULT_CAPACITY=10;
private int size;
//无参构造函数
public MyArrayList(){
}
//带List类型参数的构造函数
public MyArrayList(MyArrayList<AnyType> list){
}
//指定初始容量
public MyArrayList(int initCapacity){
if(initCapacity>0){
this.elementData=new Object[initCapacity];
}else if(initCapacity==0){
this.elementData=new Object[]{};
}else{
throw new IllegalArgumentException("不合法的数组初始容量");
}
}
public int size(){
return size;
}
//增加元素
public boolean add(AnyType e){
if(elementData.length==size()){
//数组扩容
int oldCapacity=size();
ensureCapacity(oldCapacity+(oldCapacity>>>1));//扩容为原来的1.5倍.需要注意：<<、>>、>>>的优先级低于+、-
}
elementData[size()]=e;//将元素增加至尾部
size++;//元素数量+1
return true;
}
//查询元素
public AnyType get(int index){
return (AnyType) elementData[index];
}
//修改元素
public AnyType set(int index,AnyType newVal){
AnyType oldValue=(AnyType) elementData[index];
elementData[index]=newVal;
return oldValue;
}
//删除元素
public AnyType remove(int index){
AnyType removeElement=(AnyType) elementData[index];
//index后面的元素都向前移动一位
for (int i = index; i <size()-1 ; i++) {
elementData[i]=elementData[i+1];
}
return removeElement;
}
//数组扩容
private void ensureCapacity(int newCapacity){
if(newCapacity<size()){
return;
}
Object[] newArray=new Object[newCapacity];
for (int i = 0; i <size(); i++) {
newArray[i]=elementData[i];
}
elementData=newArray;//新数组的引用赋值给旧数组
}
//forEach
public void forEach(Consumer action){
for(int i=0;i<size();i++){
action.accept(elementData[i]);
}
}
//实现Iterrable接口的iterator函数
@Override
public Iterator<AnyType> iterator() {
return new ArrayListIterator();
}
private class ArrayListIterator implements Iterator<AnyType>{
private int current=0;
@Override
public boolean hasNext() {
return current<size();
}
@Override
public AnyType next() {
if(!hasNext()){
throw new NoSuchElementException("没有元素");
}
return (AnyType) elementData[current++];
}
}
public static void main(String[] args) {
MyArrayList myArrayList=new MyArrayList(10);
for(int i=0;i<15;i++){
myArrayList.add(i);
}
System.out.println("当前元素数量为"+myArrayList.size());
System.out.println("查询元素"+myArrayList.get(0));
System.out.println("*************forEach循环遍历************");
myArrayList.forEach(e->{
System.out.println(e);
});
System.out.println("************迭代器循环遍历**********");
Iterator iterator =myArrayList.iterator();
while(iterator.hasNext()){
System.out.println("迭代"+iterator.next());
}
}
}
参考文献
1.JDK源码
2.《数据结构与算法分析》
