StringBuild与StringBuffer线程安全不安全验证

//证明StringBuffer线程安全，StringBuilder线程不安全
StringBuffer stringBuffer = new StringBuffer();
StringBuilder stringBuilder = new StringBuilder();
CountDownLatch latch1 = new CountDownLatch(1000);
CountDownLatch latch2 = new CountDownLatch(1000);
long start = System.currentTimeMillis();
for(int i=0;i<1000;i++){
    new Thread(new Runnable() {

        @Override
        public void run() {
           synchronized (stringBuilder){
               try {
                   stringBuilder.append(1);

               } catch (Exception e) {
                   e.printStackTrace();
               } finally {
                   latch1.countDown();
               }
           }
        }
    }).start();
}
long end = System.currentTimeMillis();
//System.out.println(end-start);
long start1 = System.currentTimeMillis();
for(int i=0;i<1000;i++){
    new Thread(new Runnable() {

        @Override
        public void run() {

            try {
                stringBuffer.append(1);

            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                latch2.countDown();
            }

        }
    }).start();
}
long endq = System.currentTimeMillis();
//System.out.println(endq-start1);
try {
    latch1.await();
    System.out.println("stringBuilder : "+stringBuilder.length());
    latch2.await();
    System.out.println("stringBuffer  : "+stringBuffer.length());
} catch (InterruptedException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
}