验证StringBuilder是非线程安全的Java小程序

以上程序创建了四个线程，同时向同一个StringBuilder中append字符串，运行结果：

Exception in thread "Thread-1" java.lang.ArrayIndexOutOfBoundsException
at java.lang.System.arraycopy(Native Method)
at java.lang.String.getChars(String.java:826)
at java.lang.AbstractStringBuilder.append(AbstractStringBuilder.java:416)
at java.lang.StringBuilder.append(StringBuilder.java:132)
at MyThread.run(ThreadTest.java:17)
aaaaaaaaaaaaaaaa baaa a a a a a b b b aaa ab ab a bbbb a bb aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaadaa a a d d d d d d d d c dd d d d a d d d a cc da ac c c c ad da a a a cac acc c c aa a a a cc c dcacc c c c c c c acad cc ddad cc c c c c c c d c a a a a d a d c a cdcaca cdcc c acad adad a ad a a a a a a a cc c c acacacc c c acacc c aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa