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4.7 JAVA COMPILATION PROCESS Program
Java is a platform-independent programming language. Its execution is divided into
two steps: (Source Code
Step 1: The program code is compiled into bytecode through an Operating System
independent compiler.
Step 2: This bytecode needs to be converted into machine code to execute on Compiler
an individual device. This is done by Java Virtual Machine(JVM). The JVM
performs all the tasks of the Java run-time system. It loads the Java class
file and interprets the compiled bytecode.
Bytecode
4.7.1 Java Compiler and Interpreter
The Java compiler, also known as JAVAC, converts the Java program codes (source
code) into executable files (Java bytecode). The extension of Java source code is JVM
.java. The Java compiler (JAVAC) is used to convert the java source file to a class file (Window, MacOS, Linux)
under the extension .class.
This is quite different from other languages such as C/C++. As in C/C++, the source
file is converted directly to the machine code using a compiler. But in Java, after
the compiler translates it to a .class file, the Java Virtual Machine which acts as an Machine Code
Interpreter converts it to Machine Language. JVM is designed in such a way that it
can read the source program and translate the source code line by line.
The Java compiler translates the entire program together. It generates the intermediate object code. If there is any error,
the errors are shown at once at the end of the compilation, which unless debugged the .class file will not be created.
The advantage of Java over other OOP languages is that the bytecode that is generated by the compiler can run on any
platform of operating systems where there is JVM found. This is why Java is a platform-independent language.
4.8 DIFFERENT LIBRARIES USED IN JAVA
Libraries in Java consist of different built-in classes that help the programmer to write the code. These classes are
included in Java Development Kit (JDK).
Some of the useful libraries (packages) in JDK are:
• java.lang : It is used to support classes containing String/Characters, Math, Integers, etc.
• java.io : It includes the input and output statements.
• java.applet : It contains all the required materials to develop applets.
• java.math : It contains all mathematical methods such as sqrt(), cbrt(), pow(), max(), etc.
To include the library classes, we need to write the below code before starting the program code.
Syntax:
import java.<packagename>.*;
For example,
import java.util.*;
import java.io.*;
4.9 JAVA RESERVED WORDS
Some words are used by Java for coding. These words cannot be used in the program for other purposes such as the
names of variables, classes, functions, etc. If used, it will be treated as an error by the compiler.
134134 Touchpad Computer Science-XII

