Numbers数字

This section begins with a discussion of the Number class in the java.lang package, its subclasses, and the situations where you would use instantiations of these classes rather than the primitive number types.本节首先讨论java.lang包中的Number类及其子类，以及使用这些类的实例化而不是原始数字类型的情况。

This section also presents the PrintStream and DecimalFormat classes, which provide methods for writing formatted numerical output.本节还介绍了PrintStream类和DecimalFormat类，它们提供了编写格式化数字输出的方法。

Finally, the Math class in java.lang is discussed.最后，讨论了java.lang中的Math类。It contains mathematical functions to complement the operators built into the language.它包含数学函数以补充语言中内置的运算符。This class has methods for the trigonometric functions, exponential functions, and so forth.这个类有三角函数、指数函数等的方法。