@@ -0,0 +1,399 @@
+public class StringBuilderTest %7B%0A    %0A    public static void main(String%5B%5D args) %7B%0A        //String s = %22abc%22 + nextThreadNum();%0A        //System.out.println(s);%0A        %0A        StringBuilder sb = new StringBuilder();%0A        sb.append(%22abc%22);%0A    %7D%0A    %0A    private static int threadInitNumber;%0A    private static synchronized int nextThreadNum() %7B%0A        return threadInitNumber++;%0A    %7D%0A    %0A%7D%0A

add StringBuilderTest.java