Let's Java - 3 Billion Devices!

What is Java:

Why Java?

- Remember Python is an interpreted, object-oriented, high-level programming language with dynamic semantics?

- Java implementations typically use a two-step compilation process. Java source code is compiled down to bytecode by the Java compiler. The bytecode is executed by a Java Virtual Machine (JVM). Modern JVMs use a technique called Just-in-Time (JIT) compilation to compile the bytecode to native instructions understood by hardware CPU on the fly at runtime.

- Java Development Kit (JDK) vs Java Runtime Environment (JRE) which contains the JVM

- NetBeans is an Integrated Development Environment (IDE)

- Let's install IntelliJ IDE

Main = class file or start of the application

The main() method is the first method to be called.

Java looks for this as entry point: public static void main(String[] args)

- Let's run Hello World app

- Change code to "Hello World Again!", then run again

- Let's run from command line

- End user need the JRE:

- java -version

- java Main <-- to run from java directly | Note that Main is the main entry point

- java made up statements and with ; what is Phython?

** Let's play with Java whitespace ** DIFFERENT from Python

Java comments:

// line comments

/* */ block comments

/** */ JavaDoc comments to create documentation within source code http://bit.ly/psjavadoc

1. to add human-reable notes to source code

2. "Hide" source code without deleting

Java Packages

- all lowercase

- use reversed domain name to ensure global uniqueness com.rollingcoders.example convention

- class is now com.rollingcoders.example.Main

Java requires no correlation between package names and source code file structure whereas IDE require a sub-folder for each part of package name

$ java com.rollingcoders.getorganized.Main

Hello Get Organized

/Users/htran010/Documents/Organized/out/production/Organized

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Let's tak variables

- Strongly typed language = must specify type (i.e. int datavariable = 100;

- Value can be modified

Rules

- letters, numbers, $ and _

- convention only letters and numbers are used

- first number NOT a number

- convention always a letter

- use Camel Case (i.e. bankAccountBallance, level2Training)

Primitive Data Type = Foundation of all other types

Four Categories of Primitive Types

- Integer

- Floating Point : stores fractions

- Character

- Boolean

Operators: