Write Once Run Anywhere Object-Orientation Familiar C/C++ based syntax Rich Libraries Security Internationalization Performance Its Free A community process for expanding Java

A java application is hosted o a JVM The code is complied into bytecode which is architecture-neutral Developers write code for the Java platform rather than a specific platform The byte codes are executed by the JVM and translated into native machine code by JRE.

Javacode ——>JVM —>compiled to —>bytecode

bytecode —-> JVM —> execute

Bytecode instructions —> JRE ——> translated to native machine code

JRE : Bytecode Verifier + Class Loader + JIT JIT- Just In Time compiler 

Java Community Process (JCP): specification of the API

java.sql - standard java javax.sql - JavaEE distribution JDBC-driver - database-neutral interaction with a relational database



Bytecode Verifier checks for security violations in compiled byte codes before it is executed by the JRE. Java programs run with client-specified security settings that give them specified degrees of access to local resources.

Java uses 16-bit Unicode standard localization concept

JDK1.0 20 times slower OpenJDK18 is faster as native

Java Standard Edition (SE) Language JVM Core libraries JRE JDK java java javadoc jdb

Application Server Framework for handling web components Business logic side Servlets JSP EJB JMS + Standard Edition

Defines a set of standard APIs for multi-tier enterprise scale applications Designed to work with conjunction with an application servers as Websphere

Java EE API JDBC Core API RMI-IIOP API JNDI API JDBC Extensions 2.0 EJB Servlet API JSP JMS - async messaging JTZ - Java Transaction API JavaMail - SMTP JAF - Java Activation Framework JAXP - Java API for XML Parsing JCA - Java Connector Architecture JAAS - Java Authentication and Authorization Service

Java Micro-Edition (ME) Hardly seen by developers Blu-Ray players

Download Latest version OpenJDK

JVM types HostSpot - SUN OpenJ9 - IBM

Java code must be in a class stand-alone program needs to include in main method instructions in the main method will run when execute the program Case sensitive

Java Naming Conventions Names are used to denote classes, objects, attributes and methods A name is a sequence of letters and number and _ Names may not start with a number Java names are case sensitive Class names utilize Camel cases For others starts with lower case Constants are all uppercase

Java Reserved words

abstract if throws instance catch strictfp float default private break return false volatile new goto * throw else true interface class switch package bolean import case static finally continue this double public extends void native for assert implements transient int char super null do protected byte short final while synchronized enum try long const *

package private protected public

Non-Object Data in Java

Primitives are simply variables to hold data Java provides several primitives data types: byte, short, int, long, float, double, boolean, char

Integer Types bytes short int long: with L suffix

Real Number Types float double - real number literals default to double NaN declare float with F

Creating Primitives To create a primitive, simply state its type and name separated by a space and followed by a semi-colon

int x, y, z; boolean isStarted, isEnded;

can declare primitives anywhere in your code visibility is local to where it is declared.

naming convention: low Camel Case for finals: all upper case with underscore ( Snake case)

Initialize Primitive if not assign a value to a primitive, java automatically uses default value.

Range of Primitive Types Type Default Size (bit) Min Value Max Value boolean false 1 char \u0000 16 \u0000 \uFFFF byte 0 8 -128 127 short 0 16 -32768 32767 int 0 32 -2147483648 2147483647 long 0 64 float 0.0 32 double 0.0 64

Wrapper Classes

int Integer long Long boolean Boolean

Perform mathematical and logical operations

Assignment Operator: = Mathematical operators: + - * / % Unary increment or decrement: ++ - - Relational Operators: < == > <= >= != Logical operators: && || ! Logical and Bitwise operators: & | ~ ^ << >> >>> Dot Operator: . access class member

More Assignment operators: x op= y is x = x op y +=, -=, *=, /=, %= <<=, >>=, >>>=, &=, |=, ^=

Conditional Tenaray Operator: ?:

^ : XOR

Branching

IF Statements

ELSE Statements

Nested IFs

Ternary: (x > y) > m:n;

SWITCH based on comparison can use string value since Java7

Looping

while

while(count++ < n){ } first compare count to n then count increment

do while

for

multi initialize for

for(i=0; j=2; i<10; i++, j+=3) { // i increments by 1 // j by 3 }

//java5 for-each loop loop over iterabels for(type name : collection) { // invoke methods of name } for(dataType item : array) { ... }

break

continue

types