BigInteger， BigDecimal，也是Number的派生类，初始化之后不能被改变
BigInteger a = new BigInteger("9223372036854775807"); BigInteger b = new BigInteger("2"); BigInteger c = a.multiply(b); System.out.println(c); BigDecimal a = new BigDecimal(1.0); BigDecimal b = new BigDecimal(3); BigDecimal c = a.divide(b,20,BigDecimal.ROUND_UP);
String类：Strings are immutable
创建的两种方式： String xxx = new String（）;//存在堆区
String xxx = "";//存在栈区（string pool）
字符和数字转换为String：String.valueOf(xxx);
StringBuffer/StringBuilder: an alternative to String. 比String更灵活，可以修改stringbuffer内的值，相对而言String一旦初始化就不能被修改。
StringBuffer stringbuffer = new StringBuffer(); stringbuffer.append(xxx); stringbuffer.insert(xxx); stringbuffer.delete(xxx); stringbuffer.deleteCharAt(xxx); stringbuffer.replace(xxx); stringbuffer.reverse(); stringbuffer.setCharAt(xxx);
BigInteger， BigDecimal，也是Number的派生类，初始化之后不能被改变
BigInteger a = new BigInteger("9223372036854775807"); BigInteger b = new BigInteger("2"); BigInteger c = a.multiply(b); System.out.println(c); BigDecimal a = new BigDecimal(1.0); BigDecimal b = new BigDecimal(3); BigDecimal c = a.divide(b,20,BigDecimal.ROUND_UP);String类：Strings are immutable 创建的两种方式： String xxx = new String（）;//存在堆区 String xxx = "";//存在栈区（string pool） 字符和数字转换为String：String.valueOf(xxx); StringBuffer/StringBuilder: an alternative to String. 比String更灵活，可以修改stringbuffer内的值，相对而言String一旦初始化就不能被修改。
StringBuffer stringbuffer = new StringBuffer(); stringbuffer.append(xxx); stringbuffer.insert(xxx); stringbuffer.delete(xxx); stringbuffer.deleteCharAt(xxx); stringbuffer.replace(xxx); stringbuffer.reverse(); stringbuffer.setCharAt(xxx);RegularExpressions regex正则表达式：