1. Programming Language Hierarchy, Phases of a Java Program
Prepared by
Neal Alfie Y. Lasta
IT Lecturer

2. Programming Language Hierarchy
High – Level Language (HLL)
Assembly Language
Machine Language
Hardware

3. High-Level Language (HLL)
Closest to natural language
Words, numbers, and math symbols
Not directly understood by hardware
“portable” source code (hardware independent)
Java, C, C++, COBOL, FORTRAN, BASIC, Lisp, Ada, etc.

4. Machine Language (lowest level)
Least natural language for humans, most natural language for hardware
Just 0s and 1s
Directly understood by hardware
Not portable (hardware dependent)

5. Assembly Language
A more or less human readable version of machine language
Words, Abbreviations, letters and numbers replace 0s and 1s
Easily translated from human readable to machine executable
Like machine code, not portable (hardware dependent)

6. Getting from Source Code to Machine Code
“Compiling a program” – translating from a high-level language source code to machine (object, or executable) code
“Compiler” – a program that translates HLL source code to machine (object, or executable) code
“Assembly” – translating from assemble language source code to machine (object, or executable) code
Assembler – a program that translates assembly source code to machine (object, or executable) code
Compilers need to know the specific target hardware

7. Compilers vs Assemblers vs Interpreters
Compilers and Assemblers
Translation is a separate user step
Translation is “off-line” i.e. not at run time
Interpreters
Another way to translate source to object code
Interpretation (from source to object code) is not a separable user step
Translation is “on-line” i.e. at run time

8. Compiler, Assembler or Interpreter
Source Code
object Code

9. Java Program Translation
Both compilation and interpretation
Intermediate Code:
“Byte code” – similar to assembly code, but hardware independent
Interpreter translates from generic byte code to hardware specific machine code

10. Java Byte Code
The Java compiler does not translate your program into machine language for your particular computer. Instead, the Java compiler translates your Java Program into a language called byte-code.
Byte-code -> the machine language for a hypothetical computer, which in this case, is called the Java Virtual Machine (JVM)

11. Java Virtual Machine
JVM – a software implementation or runtime environment for hosting Java applications
Interpreter works by translating each instruction of byte-code into machine language one after the other, rather than translating the entire byte-code program all at once
Java byte-code has an extension of .class. This file can be copied to another computer and when you run your program, you do not have to recompile it anymore. That makes Java portable

12. Disadvantages: Requires both compiler and interpreter
Slower program execution

13. Advantages Portability
Same program can run on computers of different types (useful with the internet)
Java compiler for new types of computers can be made quickly

14. Java Virtual Machine Data for Java Program Java Program Java Compiler
Byte-Code Program
Byte-Code Interpreter
Machine-Language Instructions
Computer Execution of Machine-Language Instructions
Output of Java Program
Java
Virtual
Machine

15. Phases of Java
See Phases of a Java Program in Book