Given this method in a class:                                                                          
                                                                                                       
21. public String toString() {                                                                         
22. StringBuffer buffer = new StringBuffer();                                                          
23. buffer.append('<');                                                                                
24. buffer.append(this.name);                                                                          
25. buffer.append('>');                                                                                
26. return buffer.toString();                                                                          
27. }                                                                                                  
                                                                                                       
Which statement is true?                                                                               
                                                                                                       
A.  This code is NOT thread-safe.                                                                      
B.  The programmer can replace StringBuffer with StringBuilder with no other changes.                  
C.  This code will perform poorly. For better performance, the code should be rewritten:               
    return "<" + this.name + ">";                                                                      
D.  This code will perform well and converting the code to use StringBuilder will not enhance the      
    performance.                                                                                       
                                                                                                       
Answer: B                                                                                              
我认为A是对的,StringBuffer虽是线程安全的,但这段代码却不是线程安全的,如果是在单线程中使用,选B当然是可以的