Java Architecture

Objectives

• Discuss the difference between an interpreter and a compiler.
• Understand what the Java Virtual Machine is and what it does.
• Understand what the Java Runtime Environment is
• Understand what the Java Development Kit is.

Notes

• I am using section 1.3 of the book
  • And other sources.
• If I have a document
  • like a program or a speech written in one language
  • that I want in another language.
  • I need to translate that document.
• In the computing world we developed several ways to do this
  • An interpreter
    • will read one line at a time and translate it to the new language.
    • But generally does not record that line.
    • So if you encounter the line again, you need to translate it again.
    • Think translating a speech in real time.
  • A compiler
    • Translates the entire document at one time to the new language
    • So it is slower at first.
    • But faster as it does not need interpreted each time.
    • Generally all syntax errors need to be removed before you can compile a program.
• Java chose both of these.
  • For portability sake, java runs on t e Java virtual Machine.
    • This is a computer emulator or virtual computer.
    • It runs a machine code called Java bytecode.
    • For each new hardware/operating system combination, the JVM must be implemented.
    • Then all java programs can be run on this platform.
    But Java bytecode is still hard to read and work with.
    • So the Java compiler translates from Java to Java bytecode.
  • You will need to install these two pieces.
    • The JRE
      • For a discussion see Oracle Documentation
      • This contains
        • The java virtual machine
        • Libraries
      • This most likely installed on your computer already.
      • But if not you will need to install this.
    • The JDK
      • This contains the java compilers
      • And other things necessary to develop code.
  • We will discuss installing both of theses in the next video.