文章目录
- 阿里巴巴开发手册强制规约:
- 1. Arrays.asList转换基本类型数组
- 2. Arrays.asList返回的List不支持增删操作
- 3. 对原始数组的修改会影响到我们获得的那个List
- 4. ArrayList.subList强转ArrayList导致异常
- 5. ArrayList中的subList切片造成OOM
- 6.Copy-On-Write 是什么?
- 7.CopyOnWriteArrayList介绍
- 8.CopyOnWriteArrayList简单源码解读
- 9.CopyOnWriteArrayList优缺点
- 10.CopyOnWriteArrayList使用场景

阿里巴巴开发手册强制规约:
1. Arrays.asList转换基本类型数组
import java.util.Arrays;
import java.util.List;
/**
* Arrays.asList数组常见问题
* @author 百里
*/
public class BaiLiTestDemo {
public static void main(String[] args) {
int[] arr = {1, 2, 3};
List list = Arrays.asList(arr);
System.out.println("list.size:" + list.size());
for (int i = 0; i < list.size(); i++) {
System.out.println("循环打印:" + list.get(i));
}
}
}
public static List asList(T... a) {
return new ArrayList<>(a);
}
import java.util.Arrays;
import java.util.List;
/**
* Arrays.asList数组常见问题
* @author 百里
*/
public class BaiLiTestDemo {
public static void main(String[] args) {
Integer[] arr = {1, 2, 3};
List list = Arrays.asList(arr);
System.out.println("list.size:" + list.size());//size = 3
for (int i = 0; i < list.size(); i++) {
System.out.println("循环打印:" + list.get(i));
}
}
}
2. Arrays.asList返回的List不支持增删操作
import java.util.Arrays;
import java.util.List;
/**
* Arrays.asList数组常见问题
* @author 百里
*/
public class BaiLiTestDemo {
public static void main(String[] args) {
Integer[] arr = {1, 2, 3};
List list = Arrays.asList(arr);
System.out.println("list.size:" + list.size());
list.add(4);
}
}
3. 对原始数组的修改会影响到我们获得的那个List
import java.util.Arrays;
import java.util.List;
/**
* Arrays.asList数组常见问题
* @author 百里
*/
public class BaiLiTestDemo {
public static void main(String[] args) {
Integer[] arr = {1, 2, 3};
List list = Arrays.asList(arr);
System.out.println("list.size:" + list.size());
arr[0] = 10;//修改原数组
for (int i = 0; i < list.size(); i++) {
System.out.println("循环打印:" + list.get(i));
}
}
}
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
/**
* Arrays.asList数组常见问题
* @author 百里
*/
public class BaiLiTestDemo {
public static void main(String[] args) {
Integer[] arr = {1, 2, 3};
List list = new ArrayList<>(Arrays.asList(arr));
arr[0] = 10;
for (int i = 0; i < list.size(); i++) {
System.out.println("循环打印:" + list.get(i));
}
}
}
4. ArrayList.subList强转ArrayList导致异常
import java.util.ArrayList;
import java.util.List;
/**
* ArrayList.subList常见问题
* @author 百里
*/
public class BaiLiArrayListDemo {
public static void main(String[] args) {
List<String> names = new ArrayList<String>() {{
add("one");
add("two");
add("three");
}};
ArrayList strings = (ArrayList) names.subList(0, 1);
System.out.println(strings);
}
}
Exception in thread "main" java.lang.ClassCastException: java.util.ArrayList$SubList cannot be cast to java.util.ArrayList
at BaiLiArrayListDemo.main(BaiLiArrayListDemo.java:15)
import java.util.ArrayList;
import java.util.List;
/**
* ArrayList.subList常见问题
* @author 百里
*/
public class BaiLiArrayListDemo {
public static void main(String[] args) {
List<String> names = new ArrayList<String>() {{
add("one");
add("two");
add("three");
}};
List strings = names.subList(0, 1);
strings.add(0,"four");
System.out.println(strings);//[four, one]
System.out.println(names);//[four, one, two, three]
}
}
import java.util.ArrayList;
import java.util.List;
/**
* ArrayList.subList常见问题
* @author 百里
*/
public class BaiLiArrayListDemo {
public static void main(String[] args) {
List<String> names = new ArrayList<String>() {{
add("one");
add("two");
add("three");
}};
List strings = names.subList(0, 1);
names.add("four");
System.out.println(strings);
System.out.println(names);
}
}
Exception in thread "main" java.util.ConcurrentModificationException
at java.util.ArrayList$SubList.checkForComodification(ArrayList.java:1231)
at java.util.ArrayList$SubList.listIterator(ArrayList.java:1091)
at java.util.AbstractList.listIterator(AbstractList.java:299)
at java.util.ArrayList$SubList.iterator(ArrayList.java:1087)
at java.util.AbstractCollection.toString(AbstractCollection.java:454)
at java.lang.String.valueOf(String.java:2994)
at java.io.PrintStream.println(PrintStream.java:821)
at BaiLiArrayListDemo.main(BaiLiArrayListDemo.java:17)
import java.util.ArrayList;
import java.util.List;
/**
* ArrayList.subList常见问题
* @author 百里
*/
public class BaiLiArrayListDemo {
public static void main(String[] args) {
List<String> names = new ArrayList<String>() {{
add("one");
add("two");
add("three");
}};
List strings = new ArrayList<>(names.subList(0, 1));
strings.add("four");
System.out.println(strings);//[one, four]
System.out.println(names);//[one, two, three]
}
}
5. ArrayList中的subList切片造成OOM
import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.IntStream;
/**
* ArrayList.subList常见问题
* @author 百里
*/
public class BaiLiArrayListDemo {
public static void main(String[] args) {
List data = new ArrayList<>();
IntStream.range(0, 1000).forEach(i ->{
List<Integer> collect =
IntStream.range(0, 100000).boxed().
collect(Collectors.toList());
data.add(collect.subList(0, 1));
});
}
}
6.Copy-On-Write 是什么?
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Iterator;
import java.util.List;
/**
* @author 百里
*/
public class BaiLiIteratorTest {
private static List<String> list = new ArrayList<>();
public static void main(String[] args) {
list.add("1");
list.add("2");
list.add("3");
Iterator<String> iter = list.iterator();
while (iter.hasNext()) {
System.err.println(iter.next());
}
System.err.println(Arrays.toString(list.toArray()));
}
}
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
/**
* 并发迭代器问题示例代码
* @author 百里
*/
public class BaiLiConcurrentIteratorTest {
// 创建一个ArrayList对象
private static List<String> list = new ArrayList<>();
public static void main(String[] args) throws InterruptedException {
// 给ArrayList添加三个元素:"1"、"2"和"3"
list.add("1");
list.add("2");
list.add("3");
// 开启线程池,提交10个线程用于在list尾部添加5个元素"121"
ExecutorService service = Executors.newFixedThreadPool(10);
for (int i = 0; i < 10; i++) {
service.execute(() -> {
for (int j = 0; j < 5; j++) {
list.add("121");
}
});
}
// 使用Iterator迭代器遍历list并输出元素值
Iterator<String> iter = list.iterator();
for (int i = 0; i < 10; i++) {
service.execute(() -> {
while (iter.hasNext()) {
System.err.println(iter.next());
try {
Thread.sleep(10);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
});
}
service.shutdown();
}
}
7.CopyOnWriteArrayList介绍
8.CopyOnWriteArrayList简单源码解读
/**
* Appends the specified element to the end of this list.
*
* @param e element to be appended to this list
* @return {@code true} (as specified by {@link Collection#add})
*/
public boolean add(E e) {
final ReentrantLock lock = this.lock;//重入锁
lock.lock();//加锁啦
try {
Object[] elements = getArray();
int len = elements.length;
Object[] newElements = Arrays.copyOf(elements, len + 1);//拷贝新数组
newElements[len] = e;
setArray(newElements);//将引用指向新数组 1
return true;
} finally {
lock.unlock();//解锁啦
}
}
@SuppressWarnings("unchecked")
public E next() {
if (! hasNext()) //是否存在下一个元素
throw new NoSuchElementException(); //没有下一个元素,则会抛出NoSuchElementException异常
//snapshot是一个类成员变量,它是在创建迭代器时通过复制集合内容而获得的一个数组。
//cursor是另一个类成员变量,初始值为0,并在每次调用next()时自增1,表示当前返回元素的位置。
return (E) snapshot[cursor++];
}
import java.util.Iterator;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
/**
* 并发迭代器问题示例代码
* @author 百里
*/
public class BaiLiConcurrentIteratorTest {
// 创建一个ArrayList对象
private static CopyOnWriteArrayList<String> list = new CopyOnWriteArrayList<>();
public static void main(String[] args) throws InterruptedException {
// 给ArrayList添加三个元素:"1"、"2"和"3"
list.add("1");
list.add("2");
list.add("3");
// 开启线程池,提交10个线程用于在list尾部添加5个元素"121"
ExecutorService service = Executors.newFixedThreadPool(10);
for (int i = 0; i < 10; i++) {
service.execute(() -> {
for (int j = 0; j < 5; j++) {
list.add("121");
}
});
}
// 使用Iterator迭代器遍历list并输出元素值
Iterator<String> iter = list.iterator();
for (int i = 0; i < 10; i++) {
service.execute(() -> {
while (iter.hasNext()) {
System.err.println(iter.next());
try {
Thread.sleep(10);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
});
}
service.shutdown();
}
}
9.CopyOnWriteArrayList优缺点
优点:
缺点: