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package collection;

import com.google.common.collect.Lists;

import java.util.ArrayList;

import java.util.Arrays;

import java.util.List;

/**

* Created by vonzhou on 2017/6/11.

*/

public class ArrayListDemo {

public static void main(String[] args) {

test1();

// test2();

// test3();

}

/**

* Exception in thread "main" java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to [Ljava.lang.String;

*/

public static void test2() {

List<String> list = new ArrayList<>();

list.add("dog");

Object[] oa = list.toArray();//其实此时数组类型已为 [Ljava.lang.Object;

System.out.println(((String) oa[0]).length());

String[] sa = (String[]) oa; // 所以此时会抛出 ClassCastException

}

public static void test1() {

// 是Arrays内部类ArrayList，而不是java.util.ArrayList

List<String> list = Arrays.asList("hello");

System.out.println(list.toArray().getClass());

Object[] oa = list.toArray();

String[] sa = (String[]) oa;// ok

String[] strArr = new String[1];

System.out.println(strArr instanceof Object[]); // true

System.out.println(new ArrayListDemo[0] instanceof Object[]); // true

}

public static void test3() {

List<String> list = Lists.newArrayList();

list.add("hello");

List<String> sub = list.subList(0, 1);

sub.add(1, "hello2");

System.out.println();

}

}