我决定优化下面的代码但遇到问题。我尝试使用this discussion将ArrayList更改为线程安全的集合，但遗憾的是出了问题。代码正在编译但抛出异常。
线程中的异常＆＃34; main＆＃34; java.lang.ClassCastException： java.util.Collections $ SynchronizedRandomAccessList无法强制转换为 java.util.ArrayList at bfpasswrd_multi.PasswordCracker.doItMulti（PasswordCracker.java:73）at at bfpasswrd_multi.PasswordCracker.runMulti（PasswordCracker.java:60）at bfpasswrd_multi.Test.main（Test.java:16）
请告诉我有什么问题？
package bfpasswrd_multi;
import java.util.Scanner;
public class Test
{
public static void main(String[] args)
{
System.out.print("Type password to be cracked: ");
@SuppressWarnings("resource")
String input = new Scanner(System.in).nextLine();
PasswordCracker cracker = new PasswordCracker();
System.out.println("Multithreaded");
cracker.runMulti(input);
cracker = new PasswordCracker();
System.out.println("Finished...");
}
}
package bfpasswrd_multi;
import java.util.ArrayList;
import java.util.Collections;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
public class PasswordCracker
{
String passwordToCrack;
public boolean passwordFound;
int min;
int max;
StringBuffer crackedPassword;
public void prepare(String text)
{
passwordToCrack = text;
passwordFound = false;
min = 48;
max = 57; // http://ascii.cl/
crackedPassword = new StringBuffer();
crackedPassword.append((char) (min - 1));
}
public void result()
{
System.out.println("Cracked Password is: " + crackedPassword.toString());
}
public void incrementString(StringBuffer toCrack, int min, int max)
{
toCrack.setCharAt(0, (char) ((int) toCrack.charAt(0) + 1));
for (int i = 0; i < toCrack.length(); i++)
{
if (toCrack.charAt(i) > (char) max)
{
toCrack.setCharAt(i, (char) min);
if (toCrack.length() == i + 1)
{
toCrack.append((char) min);
}
else
{
toCrack.setCharAt(i + 1, (char) ((int) toCrack.charAt(i + 1) + 1));
}
}
}
}
public void runMulti(String text)
{
prepare(text);
double time = System.nanoTime();
doItMulti();
time = System.nanoTime() - time;
System.out.println(time / (1000000000));
result();
}
public void doItMulti()
{
int cores = Runtime.getRuntime().availableProcessors();
ArrayList<Future<?>> tasks ; // How do I make my ArrayList Thread-Safe? Another approach to problem in Java?
// https://stackoverflow.com/questions/2444005/how-do-i-make-my-arraylist-thread-safe-another-approach-to-problem-in-java
tasks = (ArrayList<Future<?>>) Collections.synchronizedList(new ArrayList<Future<?>>(cores));
// ArrayList<Future<?>> tasks = new ArrayList<>(cores);
ExecutorService executor = Executors.newFixedThreadPool(cores);
final long step = 2000;
for (long i = 0; i < Long.MAX_VALUE; i += step)
{
while(tasks.size() > cores)
{
for(int w = 0; w < tasks.size();w++)
{
if(tasks.get(w).isDone())
{
tasks.remove(w);
break;
}
}
try
{
Thread.sleep(0);
}
catch (InterruptedException e)
{
// TODO Auto-generated catch block
e.printStackTrace();
}
}
{
final long j = i;
if (passwordFound == false)
{
tasks.add(executor.submit(new Runnable()
{
public void run()
{
long border = j + step;
StringBuffer toCrack = new StringBuffer(10);
toCrack.append(constructString3(j, min, max));
for (long k = j; k < border; k++)
{
incrementString(toCrack, min, max);
boolean found = toCrack.toString().equals(passwordToCrack);
if (found)
{
crackedPassword = toCrack;
passwordFound = found;
break;
}
}
}
}));
}
else
{
break;
}
}
}
executor.shutdownNow();
}
public String constructString3(long number, long min, long max)
{
StringBuffer text = new StringBuffer();
if (number > Long.MAX_VALUE - min)
{
number = Long.MAX_VALUE - min;
}
ArrayList<Long> vector = new ArrayList<Long>(10);
vector.add(min - 1 + number);
long range = max - min + 1;
boolean nextLetter = false;
for (int i = 0; i < vector.size(); i++)
{
long nextLetterCounter = 0;
while (vector.get(i) > max)
{
nextLetter = true;
long multiplicator = Math.abs(vector.get(i) / range);
if ((vector.get(i) - (multiplicator * range)) < min)
{
multiplicator -= 1;
}
vector.set(i, vector.get(i) - (multiplicator * range));
nextLetterCounter += multiplicator;
}
if (nextLetter)
{
vector.add((long) (min + nextLetterCounter - 1));
nextLetter = false;
}
text.append((char) vector.get(i).intValue());
}
return text.toString();
}
}
非常感谢提前！
答案 0 :(得分：1)
您所看到的问题是这一行：
tasks = (ArrayList<Future<?>>) Collections.synchronizedList(new ArrayList<Future<?>>(cores));
Collections.synchronizedList不会返回ArrayList;它确切地返回了List - java.util.Collections$SynchronizedRandomAccessList的一些子类 - 除了List之外，我对该类没有任何了解，但它不是ArrayList。
解决此问题的简单方法是将tasks声明为List<Future<?>>：
List<Future<?>> tasks =
Collections.synchronizedList(new ArrayList<Future<?>>(cores));
答案 1 :(得分：1)
亲爱的社区成员感谢您的评论。现在我的安全线程列表似乎正在运行。对于有兴趣解决方案的人，我将在下面提交已解决的代码。另外，我应该提一下，我重命名任务 要期货，请注意。大家再次感谢！
package bfpasswrd_multi;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
public class PasswordCracker
{
String passwordToCrack;
public boolean passwordFound;
int min;
int max;
StringBuffer crackedPassword;
public void prepare(String text)
{
passwordToCrack = text;
passwordFound = false;
min = 48;
max = 57; // http://ascii.cl/
crackedPassword = new StringBuffer();
crackedPassword.append((char) (min - 1));
}
public void result()
{
System.out.println("Cracked Password is: " + crackedPassword.toString());
}
public void incrementString(StringBuffer toCrack, int min, int max)
{
toCrack.setCharAt(0, (char) ((int) toCrack.charAt(0) + 1));
for (int i = 0; i < toCrack.length(); i++)
{
if (toCrack.charAt(i) > (char) max)
{
toCrack.setCharAt(i, (char) min);
if (toCrack.length() == i + 1)
{
toCrack.append((char) min);
}
else
{
toCrack.setCharAt(i + 1, (char) ((int) toCrack.charAt(i + 1) + 1));
}
}
}
}
public void runMulti(String text)
{
prepare(text);
double time = System.nanoTime();
doItMulti();
time = System.nanoTime() - time;
System.out.println(time / (1000000000));
result();
}
public void doItMulti()
{
int cores = Runtime.getRuntime().availableProcessors();
// ArrayList<Future<?>> task; // HOW IT WAS
//
// tasks = (ArrayList<Future<?>>) Collections.synchronizedList(new ArrayList<Future<?>>(cores)); // HOW IT WAS
List<Future<?>> futures ; // THE SOLUTION
futures = Collections.synchronizedList(new ArrayList<Future<?>>(cores)); // THE SOLUTION
// ArrayList<Future<?>> tasks = new ArrayList<>(cores);
ExecutorService executor = Executors.newFixedThreadPool(cores);
final long step = 2000;
for (long i = 0; i < Long.MAX_VALUE; i += step)
{
while(futures.size() > cores)
{
for(int w = 0; w < futures.size();w++)
{
if(futures.get(w).isDone())
{
futures.remove(w);
break;
}
}
try
{
Thread.sleep(0);
}
catch (InterruptedException e)
{
// TODO Auto-generated catch block
e.printStackTrace();
}
}
{
final long j = i;
if (passwordFound == false)
{
futures.add(executor.submit(new Runnable()
{
public void run()
{
long border = j + step;
StringBuffer toCrack = new StringBuffer(10);
toCrack.append(constructString3(j, min, max));
for (long k = j; k < border; k++)
{
incrementString(toCrack, min, max);
boolean found = toCrack.toString().equals(passwordToCrack);
if (found)
{
crackedPassword = toCrack;
passwordFound = found;
break;
}
}
}
}));
}
else
{
break;
}
}
}
executor.shutdownNow();
}
public String constructString3(long number, long min, long max)
{
StringBuffer text = new StringBuffer();
if (number > Long.MAX_VALUE - min)
{
number = Long.MAX_VALUE - min;
}
ArrayList<Long> vector = new ArrayList<Long>(10);
vector.add(min - 1 + number);
long range = max - min + 1;
boolean nextLetter = false;
for (int i = 0; i < vector.size(); i++)
{
long nextLetterCounter = 0;
while (vector.get(i) > max)
{
nextLetter = true;
long multiplicator = Math.abs(vector.get(i) / range);
if ((vector.get(i) - (multiplicator * range)) < min)
{
multiplicator -= 1;
}
vector.set(i, vector.get(i) - (multiplicator * range));
nextLetterCounter += multiplicator;
}
if (nextLetter)
{
vector.add((long) (min + nextLetterCounter - 1));
nextLetter = false;
}
text.append((char) vector.get(i).intValue());
}
return text.toString();
}
}