package org;

import java.util.ArrayList;
import java.util.List;

public class Test {
   static class Dog {
        public String color;
        public Integer age;

    }

    public static void main(String[] args) {
        Dog dog = new Dog();
        dog.color = "yellow";
        ArrayList<Dog> list = new ArrayList<>();
        list.add(dog);
//        list.add("2");
//        list.add("3");
        List<Dog> list2 = (List<Dog>)list.clone();
        Dog dogClone = list2.get(0);
        dogClone.color = "black";
       System.out.println(list.get(0).color + list2.get(0).color);
    }
}
// 输入的都是black

ArrayList的copy的源码

    /**
     * Returns a shallow copy of this <tt>ArrayList</tt> instance.  (The
     * elements themselves are not copied.)
     *
     * @return a clone of this <tt>ArrayList</tt> instance
     */
    public Object clone() {
        try {
            ArrayList<?> v = (ArrayList<?>) super.clone();
            v.elementData = Arrays.copyOf(elementData, size);
            v.modCount = 0;
            return v;
        } catch (CloneNotSupportedException e) {
            // this shouldn't happen, since we are Cloneable
            throw new InternalError(e);
        }
    }

  public static <T> T[] copyOf(T[] original, int newLength) {
        return (T[]) copyOf(original, newLength, original.getClass());
    }

   public static <T,U> T[] copyOf(U[] original, int newLength, Class<? extends T[]> newType) {
        @SuppressWarnings("unchecked")
        T[] copy = ((Object)newType == (Object)Object[].class)
            ? (T[]) new Object[newLength]
            : (T[]) Array.newInstance(newType.getComponentType(), newLength);
        System.arraycopy(original, 0, copy, 0,
                         Math.min(original.length, newLength));
        return copy;
    }