从线程内部修改外部对象

public void fooAndBar() {
    HashMap<Foo, Bar> fooBarMap = new HashMap<>();
    CompletionService completionService = new ExecutorCompletionService(exec);

    for(int i=0; i<10; i++) {
        completionService.submit(new Callable() {
            @Override
            public Void call() throws Exception {
                fooBarMap.put(new Foo(i), new Bar(i));
                return null;
            }
        });
    }
}
public void fooAndBar() {
    HashMap<Foo, Bar>