uni/year2/semester1/logseq-stuff/pages/Introduction to Java.md

• #CT2106 - Object-Oriented Programming
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• High-Level Language

  • Both Java and C are high-level languages and Assembly is a low-level language.
  • "High-Level" is a relative term.
    • A High-Level Language is the level of abstraction above a Low-Level Language.
    • A Low-Level Language has little or no abstraction over the machine code of a particular processor.

  • Advantages of High-Level Programming Languages

    • Easier to program.
    • Syntax can be understood by people.
    • Programs take less time to write, are shorter, & easier to read, so they are more likely to be correct.
    • Portable - they can be run on different kinds of computers.

• Translating Your Code

  • Unless you are writing Machine Code, your code has to be translated into machine code to be run on your computer.
  • There are two types of translation:
    • 1. Compilation.
      2. Interpretation

  • Compilation

    • What is a Compiler? #card card-last-interval:: 33.64 card-repeats:: 4 card-ease-factor:: 2.9 card-next-schedule:: 2022-12-18T07:44:08.310Z card-last-reviewed:: 2022-11-14T16:44:08.310Z card-last-score:: 5
      • A compiler is a program that takes human-readable source code and translates it in one go into Machine Code.
      • With compilation, "translation" occurs ^^before the program is run.^^
    • Machine Code generated by compilation is not portable.
    • However, the generated Machine Code typically executes very efficiently.
    • For big projects, the compile time can be slow.

  • Interpretation

    • Code is "translated"" on-the-fly at runtime into commands that can be executed on the machine.
    • Code is read & executed by the interpreter when the program is run.
    • Interpreted code is portable (as long as there is an interpreter).
    • Typically, interpreted code is ^^slower to run^^ as each statement has to be interpreted into machine code on-the-fly.
    • Greater chance of run-time errors.
  • ^^Java is typically both compiled and interpreted.^^
    • ^^Java is compiled to Byte Code - an intermediate language which is portable.^^
    • ^^This Byte Code is then read and executed by a Java interpreter.^^

• Java Virtual Machine (JVM)

  • What is the JVM? #card card-last-interval:: 33.64 card-repeats:: 4 card-ease-factor:: 2.9 card-next-schedule:: 2022-12-18T07:38:43.908Z card-last-reviewed:: 2022-11-14T16:38:43.909Z card-last-score:: 5
    • The Java Virtual Machine (JVM) is a piece of software - a virtual computer upon which Java byte code is executed.
  • What is the JRE? #card card-last-interval:: 28.3 card-repeats:: 4 card-ease-factor:: 2.66 card-next-schedule:: 2022-12-12T23:43:23.817Z card-last-reviewed:: 2022-11-14T16:43:23.818Z card-last-score:: 3
    • The Java Runtime Environment (JRE) contains the JVM and all the libraries required to run the Java progam.