当对字符串进行修改的时候，需要使用StringBuffer和StringBuilder类。 和String类不同的是，StringBuffer和StringBuilder类的对象能够被多次的修改，并且不产生新的未使用对象。 StringBuilder类在Java 5中被提出，它和StringBuffer之间的最大不同在于StringBuilder的方法不是线程安全 ...

Though Java already has a character type and char keyword to represent and manipulate characters, the language also requires a Character class for two reasons: Character c1 = new Character ('A'); ...