Java's standard class library provides various language-oriented APIs. Most of these APIs reside in the
java.lang package and its subpackages, although a few APIs reside in
java.math. Chapter 4 first introduces you to the
Package, Primitive Type Wrapper Class, Reference, Reflection,
System, and Threading APIs. This chapter then introduces you to
java.lang.Math class declares
PI that represent the natural logarithm base value (2.71828...) and the ratio of a circle's circumference to its diameter (3.14159...).
E is initialized to