我希望你们一切都好。所以来到这个问题。我有这部分代码：
private static ArrayList<String> primelist = new ArrayList<>();
static void addToList(String list_elm) {
primelist.add(list_elm);
}
基本上，我在完整代码（如下）中创建的多个线程同时访问此列表，这些线程负责进行一些计算并返回结果，然后primelist通过调用方法将其添加到此列表中addToList(String list_elm)。
但是，在所有线程都被终止（即：完成它们的工作）之后，在primelist. 因此，经过一番研究，事实证明 ArrayList 不是线程安全的类，因此它的方法也不是。我想问以下（也许很深）问题：
线程在执行一行代码时是否会被放入（等待//定时等待）..，也就是说它正在调用该方法addToList(String list_elm)并且它到达了该行primelist.add(list_elm);但是在添加元素时它恰好停止了！
如果不能，请澄清我对（尤其是）ArrayList 案例的困惑。（（基本上是怎么回事？^^））
完整代码：
import java.util.ArrayList;
import java.util.Iterator;
public class CreatingAThreadThree
{
private static ArrayList<String> primelist = new ArrayList<>();
static void addToList(String list_elm)
{
primelist.add(list_elm);
}
static ArrayList<String> getListReference(){
return primelist;
}
public static void main(String[] args)
{
for(long x = 6223372036854775899L; x<=(6223372036854775999L); x+=2)
{
new Thread (new MyCalcRunnable(x)).start();
}
for(long x = 9223372036854774703L; x<=9223372036854774789L; x+=2 )
{
new MyCalcThread(x, "myChildThread"+x);
}
Thread mainThread = Thread.currentThread();
int spinner =0;
char animation = ' ';
System.out.println("Total number of active threads: " + Thread.activeCount());
System.out.print("Calculating primes: ");
while(Thread.activeCount() >1)
{
spinner ++;
switch(spinner)
{
case 1:
animation = '|';
break;
case 2:
animation = '/';
break;
case 3:
animation = '-';
break;
case 4:
animation = '\\';
spinner = 0;
break;
}
System.out.print("\b" + animation);
try
{
Thread.sleep(200);
}catch(InterruptedException ex)
{
}
}
System.out.println("Total number of active threads: " + Thread.activeCount());
System.out.println("Results List:");
Iterator<?> iterator = (getListReference().iterator());
while(iterator.hasNext())
{
System.out.println(iterator.next());
}
}
}
class MyCalcThread extends Thread
{
private long numberToFactor = 0;
MyCalcThread(long numberToFactor, String name)
{
super(name);
this.numberToFactor = numberToFactor;
start();
}
@Override
public void run()
{
CreatingAThreadThree.addToList(new PrimeStuff().isItPrime(this.numberToFactor));
}
}
class MyCalcRunnable implements Runnable
{
private long numberToFactor = 0;
MyCalcRunnable(long numberToFactor)
{
this.numberToFactor = numberToFactor;
}
@Override
public void run()
{
CreatingAThreadThree.addToList(new PrimeStuff().isItPrime(this.numberToFactor));
}
}
class PrimeStuff
{
String isItPrime(long numberToFactor)
{
if(numberToFactor % 2 == 0)
return (numberToFactor +"is Not prime....divisible by 2");
long squareRoot = (long)(Math.sqrt(numberToFactor));
for(long i=3; i<squareRoot; i++)
{
if(numberToFactor % i == 0)
{
return (numberToFactor +"is Not prime....first divisible by " + i);
}
}
return (numberToFactor + " is Prime!!");
}
}