通过反射查看ArrayList扩容机制

import java.lang.reflect.Field;
import java.util.ArrayList;

public class Test {

    public static void main(String[] args) throws ClassNotFoundException, NoSuchFieldException, IllegalAccessException {
        ArrayList<Integer> list = new ArrayList<Integer>();
        for (int i = 0; i < 11; i++) {
            list.add(i);
        }

        Class c = Class.forName("java.util.ArrayList");
        Field f = c.getDeclaredField("elementData");
        f.setAccessible(true);
        Object[] o = (Object[])f.get(list);
        System.out.println(o.length);

    }
}