Getting to Know Java - Beginning Java Programming: The Object-Oriented Approach - page 15

public static void calculateBMI();
Code:
0: getstatic #22 // Field weight:D
3: getstatic #26 // Field height:D
6: getstatic #26 // Field height:D
9: dmul
10: ddiv
11: putstatic #44 // Field BMI:D
14: return
}

When compared to a pure interpreter technology, errors are detected during compilation time
instead of during execution time. When compared to a pure compiler technology, the portability
is better since this setup essentially implements a “write once, compile, run everywhere” strat-
egy so that every platform with a Java Virtual Machine can run Java bytecode. This is espe-
cially relevant in a networked (Internet) environment with many host systems having their own
specific platform.

Windows

Interpreter

BMI.class

BMI.java

Mac OS

public class BMIcalculator { ---------------------------------

------------------
------------
----------------

double weight;
double height;
double BMI;

Interpreter

....

Sun Solaris

Interpreter

Compiler

figure 2-1

Java runtime environment (Jre)
The Java Runtime Environment (JRE) is the software environment in which Java programs run. It
consists of various components, as depicted in Figure 2-2.

The next subsections elaborate on the following components:
➤

Java API (Application Programming Interface)

➤

Class loader

➤

Bytecode verifier

➤

Java Virtual Machine (JVM)