Java Essential Training

• Java 8 and 11 are the two stable versions
• Java 11 uses the Type Inference i.e. usage of var.

History

• A new portable language
• Original Name: Oak
• Tag line: Write once, Run Everywhere

Principles of JAVA

• Simple, Object-oriented, and familiar
• Robust and secure(Methods, properties and Debugging)
• Architecture-neutral and portable
• High-performance
• Interpreted, threaded(more than one processes) and dynamic

Runtime Architecture

• It is an interpreted language.
• It compiles the bytecode instead of machine language
• The compiled application is portable between platforms without recompiling(JVM)

Java and JavaScript

Java features

• Java Platform, Micro Edition(ME) (Micro-Controller, sensors and mobile devices)
• Java Runtime Environment (Java SE Runtime Environment (JRE) includes JVM), Supported on Windows, Linux, OS X and Solaris, Runs all java applications: desktop, browser and server, Must be updated to keep up with the security issues, Mobile operating systems have their own runtimes.
• Java development kit(JDK): It is a no cost from ORACLE, Include tools for the compilation and packaging
  
  • java: runtime
  • javac: compile
  • javadoc: docs builder
  • jar: archive builder

Creating the JAVA classes

• All codes are defined in classes
• Classes are defined in the src code files with .java extensions
• javac command compiles Java code into byte code

Identifier Conventions

• Classes start with the uppercase character, class MyClass{}
• Methods and variables start with the lowercase character.
  

    void doSomething() {
    }

• Constants are always UpperCase

    public static final String FIRST_NAME = "david";

Memory management and Garbage collection

• Automatic Memory Management (Memory for objects is allocated automatically)
• Objects are created in the heap memory
• As long as any variable references an object, its's retained
• When all the references expire, then it is available for the garbage collection

Reference Expire?

• Variables local to methods or code blocks expire with scope,
  

    void checkString() {
        String localVar = "Test String";
        System.out.println("Tes" + localVar);
    }

• We can defer variable with the null keyword, String tempVar = "Test string"; tempVar = null;