[Java] #1 Java11: Intro

This is a self note while taking the online course from: LinkedIn Learning: Java 11+ Essential Training by David Gassner

---

1. Principle of Java

• Simple, object-oriented, and familiar
• Robust and secure –> designing everything as object

• Architecture neutral and portable

  • compiles to byte code (not machine code) –> can be loaded on any operating system that has a Java virtual machine

  • applications are portable between platforms without recompiling

    Java runtime architecture:

• High performance
• Interpreted, threaded, and dynamic
  • compiled to a format that’s interpreted at run time (directly machine code X) ==> interpreted
  • easy to build application do more than one thing at the same time ==> threaded(multi-threads)

2. Java syntax

• Java Class file

  • all code is defined in classes
  • java source code (.java file) can be compiled using javac command
  • java command runs the compiled bytecode file with JVM

  pacakge com.example; // 1)
  
  public class Main { // 2)
      public static void main(String[] args) {
          System.out.println("Hello World");
      }
  }
  

  • 1. package declaration: indicates where the file is stored in terms of the directory structure of the application (organizing the code)
  • 1. class declaration: class name + class members + main method

• Identifier Conventions

  • Classes start with an uppercase character
  • Method, variables start with an lowercase character
  • Constants are all uppercase

3. Memory Management in Java

• Java automatically allocates and deallocates memory as needed (in runtime)
• Local variables, function calls –> Stack
• Objects, member variables –> Heap
• Objects are reatained in memory until dereferenced
• After dereferenced –> Garbage Collector

Tips for memory management:

• minimize the number of objects
• use System methods to check memory usage (Runtime.maxMemory(), Runtime.totalMemory(), …)