public class ArrayList {
    Object[] elementData;
    public boolean contains(Object o) {
        for (int i = 0; i < elementData.length; i++) {
            if (o.equals(elementData[i])) {    //o可能是null，这里应该是Objects.equals(o,elementData[i])吧
                return true;                   //我猜Objects.equals可能是先判断是否为null,再调用传入实例的equals方法
            }
        }
        return false;
    }
}