multithreading - Java - Filling an ArrayList of Threads with loop -

this question pretty easy answer don't it. reduced problem until little piece of code left in order find "origin" of problem: i'm trying fill arraylist of threads loop.

public static int u=0;  public void test(){     while (u <10) {         synchronized(threadlist){             threadlist.add(u, new thread(){                                 @override public void run(){                                         system.out.println("thread @ index: " + u);                                      }              });         }         u++;                 }      threadlist.get(2).start();     } 

with last line wanted test loop above starting thread @ index '2'. i'm expecting console show "thread @ index: 2" instead shown: "thread @ index: 10" no matter integer write in ".get(int)"-method, receive index '10'.

why that? , how fix this?

the creation of threads seems work...so integer 'u' problem?

i appreciate kind of help! in advance!

when reference u in run method

@override public void run(){                         system.out.println("thread @ index: " + u);                      }  

the current value of u retrieved. @ end of loop , when thread runs, value 10.

try following

public static int u = 0;  public void test(){     while (u <10) {         synchronized(threadlist){             threadlist.add(u, new thread(){                      int = u;                  @override public void run(){                                         system.out.println("thread @ index: " + i);                                      }              });         }         u++;                 }      threadlist.get(2).start();     } 

in anonymous thread class, you're setting instance field i value u has when constructor called , printing value when run() executed.

you reference u in context hasn't been executed yet, thread. when run() method gets called, program evaluate variable u, @ point in execution of program, value 10. if, instead, above, variable i hold value @ exact moment. because when new thread gets started , executed, field initialization occurs , u evaluated right away.