说明都在注释:
package adt.array;
import java.util.Iterator;
import java.util.NoSuchElementException;
/**
*
* @author 数据结构与算法分析
* @param <T> AnyType T 任何类型
*/
public class MyArrayList<T> implements Iterable<T>{
//集合初识长度
private static final int DEFAULT_CAPACITY = 10;
//当前List数据长度
private int theSize;
//底层数组集合
private T[] theItems;
//长度
public int size() {
return theSize;
}
//List判空
public boolean isEmpty() {
return size() == 0;
}
/***
* 扩充长度
*/
public void trimToSize() {
ensureCapacity(size());
}
/***
*根据下标获取数据，如果下标为负数或大于当前数组长度，抛出数组越界异常。
* @param idx
* @return
*/
public T get(int idx) {
if(idx < 0 || idx >= size()) {
throw new ArrayIndexOutOfBoundsException();
}
return theItems[ idx ];
}
//初始化
public MyArrayList() {
doClear();
}
//清除长度，将当前集合长度变为初始值
private void doClear() {
theSize = 0;
ensureCapacity(DEFAULT_CAPACITY);
}
/***
* 如果当前需要扩充的长度小于当前数组长度，那么程序将不往下执行
* 否则获取当前数组，创造新的数组，新的数组长度根据newCapacity进行初始化，
* 然后将旧的数组赋给新的数组
* @param newCapacity
*/
@SuppressWarnings("unchecked")
private void ensureCapacity(int newCapacity) {
if(newCapacity < theSize)
return;
T[] old = theItems;
theItems = (T []) new Object[ newCapacity ];
for(int i = 0; i < size(); i++)
theItems[i] = old[i];
}
//清空集合
public void clear() {
doClear();
}
/**
* 更新数据，根据下标，判断下标是否越界，接着根据下标获取当前下标的数据进行覆盖
* @param idx
* @param newVal
* @return
*/
public T set(int idx, T newVal) {
if(idx < 0 || idx >= size()) {
throw new ArrayIndexOutOfBoundsException();
}
T old = theItems[ idx ];
theItems[idx] = newVal;
return old;
}
//添加一个数据，在最后
public boolean add(T x) {
add(size(), x);
return true;
}
/**
* 在上一个add方法中将数组长度传入，如果当前长度满了，那么扩充一倍(+1用于大小是0的情况)
* 接着将所有数据向后移一位，将输入插入到第一位index0，长度自增。
* @param idx
* @param x
*/
public void add(int idx,T x) {
if(theItems.length == size())
ensureCapacity(size()*2+1);
for(int i = theSize; i > idx; i--)
theItems[i] = theItems[i-1];
theItems[idx] = x;
theSize++;
}
/**
* 都差不多
* @param idx
* @return
*/
public T remove(int idx) {
T removeItem = theItems[idx];
for(int i = idx; i < size() -1; i++)
theItems[ i ] = theItems[ i +1 ];
theSize--;
return removeItem;
}
//实现迭代器
@Override
public Iterator<T> iterator() {
return new ArrayListIterator();
}
//具体实现
private class ArrayListIterator implements Iterator<T>{
private int current = 0;
@Override
public boolean hasNext() {
return current < size();
}
@Override
public T next() {
if(!hasNext())
throw new NoSuchElementException();
return theItems[current ++];
}
public void remove() {
MyArrayList.this.remove(-- current);
}
}
}
package adt.array;
public class MainTest {
//简单测试
public static void main(String[] args) {
MyArrayList<String> myArrayList = new MyArrayList<>();
for(int i = 0; i < 100; i++) {
myArrayList.add(RandomStr());
}
myArrayList.forEach(str->{
System.out.println(str);
});
}
public static String RandomStr() {
String strArr = "QaWsEdRfTgYhUjIkOlqPwAeDrFGyHuJiKopLZzxXcCVbBbNnmM";
return strArr.substring((int)(Math.random()*strArr.length()));
}
}
输出:
yHuJiKopLZzxXcCVbBbNnmM cCVbBbNnmM NnmM DrFGyHuJiKopLZzxXcCVbBbNnmM DrFGyHuJiKopLZzxXcCVbBbNnmM AeDrFGyHuJiKopLZzxXcCVbBbNnmM DrFGyHuJiKopLZzxXcCVbBbNnmM yHuJiKopLZzxXcCVbBbNnmM LZzxXcCVbBbNnmM sEdRfTgYhUjIkOlqPwAeDrFGyHuJiKopLZzxXcCVbBbNnmM QaWsEdRfTgYhUjIkOlqPwAeDrFGyHuJiKopLZzxXcCVbBbNnmM jIkOlqPwAeDrFGyHuJiKopLZzxXcCVbBbNnmM UjIkOlqPwAeDrFGyHuJiKopLZzxXcCVbBbNnmM AeDrFGyHuJiKopLZzxXcCVbBbNnmM qPwAeDrFGyHuJiKopLZzxXcCVbBbNnmM gYhUjIkOlqPwAeDrFGyHuJiKopLZzxXcCVbBbNnmM zxXcCVbBbNnmM M zxXcCVbBbNnmM BbNnmM iKopLZzxXcCVbBbNnmM fTgYhUjIkOlqPwAeDrFGyHuJiKopLZzxXcCVbBbNnmM KopLZzxXcCVbBbNnmM BbNnmM ZzxXcCVbBbNnmM bNnmM JiKopLZzxXcCVbBbNnmM gYhUjIkOlqPwAeDrFGyHuJiKopLZzxXcCVbBbNnmM pLZzxXcCVbBbNnmM lqPwAeDrFGyHuJiKopLZzxXcCVbBbNnmM CVbBbNnmM ZzxXcCVbBbNnmM qPwAeDrFGyHuJiKopLZzxXcCVbBbNnmM BbNnmM dRfTgYhUjIkOlqPwAeDrFGyHuJiKopLZzxXcCVbBbNnmM eDrFGyHuJiKopLZzxXcCVbBbNnmM YhUjIkOlqPwAeDrFGyHuJiKopLZzxXcCVbBbNnmM gYhUjIkOlqPwAeDrFGyHuJiKopLZzxXcCVbBbNnmM EdRfTgYhUjIkOlqPwAeDrFGyHuJiKopLZzxXcCVbBbNnmM KopLZzxXcCVbBbNnmM TgYhUjIkOlqPwAeDrFGyHuJiKopLZzxXcCVbBbNnmM UjIkOlqPwAeDrFGyHuJiKopLZzxXcCVbBbNnmM PwAeDrFGyHuJiKopLZzxXcCVbBbNnmM JiKopLZzxXcCVbBbNnmM M YhUjIkOlqPwAeDrFGyHuJiKopLZzxXcCVbBbNnmM WsEdRfTgYhUjIkOlqPwAeDrFGyHuJiKopLZzxXcCVbBbNnmM HuJiKopLZzxXcCVbBbNnmM iKopLZzxXcCVbBbNnmM uJiKopLZzxXcCVbBbNnmM gYhUjIkOlqPwAeDrFGyHuJiKopLZzxXcCVbBbNnmM LZzxXcCVbBbNnmM nmM xXcCVbBbNnmM uJiKopLZzxXcCVbBbNnmM WsEdRfTgYhUjIkOlqPwAeDrFGyHuJiKopLZzxXcCVbBbNnmM XcCVbBbNnmM rFGyHuJiKopLZzxXcCVbBbNnmM opLZzxXcCVbBbNnmM QaWsEdRfTgYhUjIkOlqPwAeDrFGyHuJiKopLZzxXcCVbBbNnmM IkOlqPwAeDrFGyHuJiKopLZzxXcCVbBbNnmM HuJiKopLZzxXcCVbBbNnmM mM bNnmM BbNnmM bNnmM KopLZzxXcCVbBbNnmM GyHuJiKopLZzxXcCVbBbNnmM CVbBbNnmM uJiKopLZzxXcCVbBbNnmM EdRfTgYhUjIkOlqPwAeDrFGyHuJiKopLZzxXcCVbBbNnmM WsEdRfTgYhUjIkOlqPwAeDrFGyHuJiKopLZzxXcCVbBbNnmM CVbBbNnmM fTgYhUjIkOlqPwAeDrFGyHuJiKopLZzxXcCVbBbNnmM lqPwAeDrFGyHuJiKopLZzxXcCVbBbNnmM DrFGyHuJiKopLZzxXcCVbBbNnmM mM NnmM dRfTgYhUjIkOlqPwAeDrFGyHuJiKopLZzxXcCVbBbNnmM DrFGyHuJiKopLZzxXcCVbBbNnmM BbNnmM QaWsEdRfTgYhUjIkOlqPwAeDrFGyHuJiKopLZzxXcCVbBbNnmM VbBbNnmM DrFGyHuJiKopLZzxXcCVbBbNnmM DrFGyHuJiKopLZzxXcCVbBbNnmM cCVbBbNnmM LZzxXcCVbBbNnmM OlqPwAeDrFGyHuJiKopLZzxXcCVbBbNnmM NnmM PwAeDrFGyHuJiKopLZzxXcCVbBbNnmM KopLZzxXcCVbBbNnmM NnmM GyHuJiKopLZzxXcCVbBbNnmM CVbBbNnmM HuJiKopLZzxXcCVbBbNnmM wAeDrFGyHuJiKopLZzxXcCVbBbNnmM XcCVbBbNnmM wAeDrFGyHuJiKopLZzxXcCVbBbNnmM gYhUjIkOlqPwAeDrFGyHuJiKopLZzxXcCVbBbNnmM PwAeDrFGyHuJiKopLZzxXcCVbBbNnmM