stringBuffer多次append

CountDownLatch countDownLatch = new CountDownLatch(2);
StringBuffer stringBuffer = new StringBuffer();
ExecutorService executorService = Executors.newFixedThreadPool(2);
executorService.execute(() -> {
	try {
		Thread.currentThread().sleep(20);
	} catch (InterruptedException e) {
		e.printStackTrace();
	}
	stringBuffer.append("1").append("1").append("1").append("1").append("1").append("1").append("1").append("1").append("1").append("1").append("1").append("1").append("1").append("1").append("1").append("1").append("1").append("1");
	countDownLatch.countDown();
});
executorService.execute(() -> {
	try {
		Thread.currentThread().sleep(20);
	} catch (InterruptedException e) {
		e.printStackTrace();
	}
	stringBuffer.append("2").append("2").append("2").append("2").append("2").append("2").append("2").append("2").append("2").append("2").append("2").append("2").append("2").append("2");
	countDownLatch.countDown();
});


// executorService.execute(() -> {
// 	try {
// 		Thread.currentThread().sleep(20);
// 	} catch (InterruptedException e) {
// 		e.printStackTrace();
// 	}
// 	stringBuffer.append("1" + "1" + "1" + "1" + "1" + "1" + "1" + "1" + "1" + "1" + "1" + "1" + "1" + "1" + "1" + "1" + "1" + "1" + "1" + "1" + "1" + "1" + "1" + "1" + "1" + "1" + "1" + "1"
// 	+ "1" + "1" + "1" + "1" + "1" + "1" + "1");
// 	countDownLatch.countDown();
// });
// executorService.execute(() -> {
// 	try {
// 		Thread.currentThread().sleep(20);
// 	} catch (InterruptedException e) {
// 		e.printStackTrace();
// 	}
// 	stringBuffer.append("2" + "2" + "2" + "2" + "2" + "2" + "2" + "2" + "2" + "2" + "2" + "2" + "2" + "2" + "2" + "2" + "2" + "2" + "2" + "2" + "2" + "2" + "2" + "2" + "2" + "2" + "2" + "2"
// 	+ "2" + "2" + "2" + "2" + "2" + "2" + "2" + "2" + "2" + "2" + "2" + "2");
// 	countDownLatch.countDown();
// });
countDownLatch.await();
executorService.shutdown();
System.out.println(stringBuffer);

stringBuffer的每次append是线程安全的,单多个是会出现问题,多个还是要用字符串连接stringBuffer多次append