String,StringBuffer跟StringBuilder比较
String,StringBuffer和StringBuilder比较String,StringBuffer,StringBuilder这三个类都实现了同样的接口，j
String,StringBuffer和StringBuilder比较
String,StringBuffer,StringBuilder这三个类都实现了同样的接口，java.io.Serializable, Comparable<String>, CharSequence也就是说他们大概的功能都是相同的，但是因为某些微小的变化导致了他们存在一些功能的差异。
首先：String一旦new出来值将不会改变，
????? JDK分析
????? private final char value[];
????? StringBuffer,StringBuilder的值都是可以改变的，
????? char value[];
第二：StringBuffer,StringBuilder性能差异
?????? StringBuffer线程安全的
/** * A thread-safe, mutable sequence of characters. * A string buffer is like a {@link String}, but can be modified. At any * point in time it contains some particular sequence of characters, but * the length and content of the sequence can be changed through certain * method calls. * <p> * String buffers are safe for use by multiple threads. The methods * are synchronized where necessary so that all the operations on any * particular instance behave as if they occur in some serial order * that is consistent with the order of the method calls made by each of * the individual threads involved. * <p> * The principal operations on a <code>StringBuffer</code> are the * <code>append</code> and <code>insert</code> methods, which are * overloaded so as to accept data of any type. Each effectively * converts a given datum to a string and then appends or inserts the * characters of that string to the string buffer. The * <code>append</code> method always adds these characters at the end * of the buffer; the <code>insert</code> method adds the characters at * a specified point. * <p>
?? 而StringBuilder却不是的，
/** * A mutable sequence of characters. This class provides an API compatible * with <code>StringBuffer</code>, but with no guarantee of synchronization. * This class is designed for use as a drop-in replacement for * <code>StringBuffer</code> in places where the string buffer was being * used by a single thread (as is generally the case). Where possible, * it is recommended that this class be used in preference to * <code>StringBuffer</code> as it will be faster under most implementations. *
综合而言，String的值无法改变，StringBuffer,StringBuilder可以，但是StringBuilder的性能比
StringBuffer更高。
