StringBuffer 需要注意的地方--final
StringBuffer 需要注意的地方如下，如果StringBuffer 变量被final修饰后：
package test;
public class TestBuffer {
public static void main(String[] args) {
final StringBuffer sb = new StringBuffer().append("abc");
sb.append("EF");
System.out.println(sb);
}
}
输出结果：
abcEF
在JavaSE的官方文档上：
http://docs.oracle.com/javase/specs/jls/se7/html/jls-4.html#jls-4.12.4
说明如下：
Once a final variable has been assigned, it always contains the same value. If a final variable holds a reference to an object, then the state of the object may be changed by operations on the object, but the variable will always refer to the same object.
So it is OK to manipulate state of object pointed by a
sb.append("Welcome"); //is OK but you can't make a to point to another object
final StringBuffer a = new StringBuffer("Hello");
a = new StringBuffer("World"); //this wont compile参考2：http://www.javaranch.com/journal/2003/04/immutable.htm
Which classes are Immutable?
To finish up, lets discuss the common Java classes that are immutable and those that aren't. Firstly, all of the java.lang package wrapper classes are immutable:Boolean, Byte, Character, Double, Float, Integer, Long, Short, String.
As in the Person classes we discussed, java.util.Date objects are not immutable. The classes java.math.BigInteger and BigDecimal are not immutable either, although maybe they should have been