初始 ArrayList 长度 4，长度不足容量翻倍策略，随机创建一百万个对象，统计时间，为什么会有两次变化呢？

public static void main(String[] args) {
DVDCollection movies = new DVDCollection();
String str="abcdefghijklmnopqrstuvwxyz";
Random random=new Random();
long start=System.currentTimeMillis();
for(int i=0;i<10;i++) {
for(int j=0;j<100000;j++) {

     int titleNum=random.nextInt(26);
     int dirNum=random.nextInt(26);
     int year=random.nextInt(26);
     double cost=random.nextDouble()*20;
     boolean bluray;
     String title=str.charAt(titleNum)+"a";
     String director=str.charAt(dirNum)+"a";
     if(random.nextInt()%2==0) {
         bluray=true;
     }
     else
         bluray=false;
            movies.addDVD(title, director, year, cost, bluray);
        }
        long end=System.currentTimeMillis();
        long timeElapsed=end-start;
        System.out.println(timeElapsed);
    }   
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    public class DVDCollection {
private DVD[] collection;
private int count;
private double totalCost;
public DVDCollection() {
    collection=new DVD[4];
    count=0;
    totalCost=0.0;
}

public void addDVD(String title,String director,int year,
        double cost,boolean bluray) {
    if(count==collection.length)
        increaseSize();

    collection[count]=new DVD(title,director,year,cost,bluray);
    totalCost+=cost;
    count++;
}
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https://blog.csdn.net/a15920804969/article/details/78422509