java 多线程代码优化

多线程代码如下：
/**多线程处理ArrayList<SsqIssue> AL
 * AL.get(i).getRedBalls()与 issuesAll.get(j).getRedBalls()比较，有a_numlimit个数据相同的，那么就从AL中删除AL.get(i)
 * 
 * @param AL
 * @param issuesAll
 * @param a_numlimit
 * @return
 */
public static List<SsqIssue> dealListWithMutiThread(ArrayList<SsqIssue> AL,ArrayList<SsqIssue> issuesAll,int a_numlimit){  
    int index = 0;
    int dealSize = 500000;
    int b=AL.size()/dealSize+1;
    ExecutorService ex = Executors.newFixedThreadPool(b);   
    ArrayList<Future<ArrayList<SsqIssue>>> futures=new  ArrayList<Future<ArrayList<SsqIssue>>>();
            //分配    try {
        //处理
     ArrayList<SsqIssue>  result = new ArrayList<SsqIssue>();
        SelectResult.toFile(  VeDate.getStringDate() +" begin try and get Future; result.size()="+ result.size());
    
        for(int i=0;i<= b;i++,index+=dealSize){
            int start = index;
            if(start>=AL.size()) break;
            int end = start + dealSize;
            end = end>AL.size() ? AL.size()-1 : end;
            //打日志
            SelectResult.toFile(  VeDate.getStringDate() +"  start="+start+" end="+end);
            Future<ArrayList<SsqIssue>> f = ex.submit(new Task(AL,issuesAll,start,end,a_numlimit));
            futures.add(f);
        }
       //打日志
        SelectResult.toFile("  futures.size()="+futures.size());
     ArrayList<Integer> redb  =new ArrayList<Integer>();
     ArrayList<SsqIssue> s=new ArrayList<SsqIssue>();
        for(Future<ArrayList<SsqIssue>> future : futures){
            //合并操作        
         if(future!=null&&future.get()!=null) {s.addAll(future.get());}
            result.addAll(s);
        }
       
        SelectResult.toFile(  VeDate.getStringDate() +"   try end; result.size()=" + result.size());
        return result;
    } catch (Exception e) {
        e.printStackTrace();
        return null;
    }
    
}
 
private static class Task implements Callable<ArrayList<SsqIssue>>{          
        private  ArrayList<SsqIssue> AL;
        private ArrayList<SsqIssue> issuesAll;
        private int start;
        private int end;
        private int a_numlimit;
         
        public Task(ArrayList<SsqIssue> ALl,ArrayList<SsqIssue> issuesAll,int start,int end,int a_numlimit){
        
            this.AL = new ArrayList<SsqIssue>(ALl.subList(start, end));
            for(int i=start;i<ALl.size()&&i<end;i++){
             this.AL.add(ALl.get(i));
            }
            this.issuesAll=issuesAll;
            this.start = start;
            this.end = end;
            this.a_numlimit=a_numlimit;
        }
 
        public ArrayList<SsqIssue> call() throws Exception {
         SelectResult.toFile(  VeDate.getStringDate() +"Task("+ this.AL.size()+" ,"+ issuesAll.size()+","+ start+","+ end+","+ a_numlimit+")" );
         for(int i=0;i<this.AL.size();i++){
     log("AL.size()="+this.AL.size());
     for(int j=0;j<issuesAll.size();j++){
    
     //log("Thread.currentThread().getName()="+Thread.currentThread().getName() +"|| AL.size()="+AL.size()); 
      SsqIssue SI=new  SsqIssue();
      
       SI.setBlueBall(this.AL.get(i).getBlueBall());
       SI.setRedBalls(this.AL.get(i).getRedBalls());
       SI.setIssue(this.AL.get(i).getIssue());
       SI.setIdx(this.AL.get(i).getIdx());
     if(mycontains(SI.getRedBalls(),issuesAll.get(j).getRedBalls(),a_numlimit)){
     if(this.AL.get(i)!=null){
     this.AL.remove(SI);
     }
    
     }
       }  
      }
            //返回处理结果
            return this.AL;
        }
    }调用多线程代码如下： List<SsqIssue> AL2=new ArrayList<SsqIssue>();
AL2=dealListWithMutiThread(AL,issuesAll,a_numlimit);
log("!!!AL2.size()="+AL2);
控制台报错信息如下：
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
java.util.concurrent.ExecutionException: java.lang.NullPointerException
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: !!!AL2.size()=null
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
at java.util.concurrent.FutureTask.report(Unknown Source)
at java.util.concurrent.FutureTask.get(Unknown Source)
at com.fh.xt.MySsqStaticstic.dealListWithMutiThread(MySsqStaticstic.java:3376)
at com.fh.xt.MySsqStaticstic.selectSsqLL(MySsqStaticstic.java:1444)
at com.fh.xt.MySsqStaticstic.main(MySsqStaticstic.java:203)
Caused by: java.lang.NullPointerException
at com.fh.xt.MySsqStaticstic$Task.call(MySsqStaticstic.java:3414)
at com.fh.xt.MySsqStaticstic$Task.call(MySsqStaticstic.java:1)
at java.util.concurrent.FutureTask.run(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
MySsqStaticstic: AL.size()=1429478
Exception in thread "main" java.lang.NullPointerException
at java.util.ArrayList.addAll(Unknown Source)
at com.fh.xt.MySsqStaticstic.selectSsqLL(MySsqStaticstic.java:1447)
at com.fh.xt.MySsqStaticstic.main(MySsqStaticstic.java:203)请问各位何解？？？