/Oracle-Java

Primary LanguageJava

Chapter 1 - Java Fundamentals

The Origins of Java

  • Java was conceived by James Goling, Patrick Naughton, Chris Warth, Ed Frank, and Mike Sheridan at Sun Microsystems in 1991

  • purpose is to create consumer electronic devices such as toasters, microwave oven and remote control.

  • Problem is most computer languages were design into machine code that specific only in the target CPU.

  • Attempt to find better solution, Gosling and the others worked on a portable, cross-platform language that could produce a code in any CPU's and Environments

  • It was the Internet that ultimately led to Java's large-scale success.

Java's Lineage: C and C++

  • Java's closest ancestor are C and C++.

  • From C, Java inherits its syntax

  • Java's Object model is adapted from C++.

Java's Magic: The Bytecode

  • The key that allowed Java to address both the security and the portability problems is that the output of a Java compiler is not executable, rather its a bytecode.

  • Bytecode is a highly optimized set of instructions that can be executed via Java Virtual Machine, which is a part of Java Runtime Environment(JRE).

  • JVM was designed as an interpreted of bytecodes.

Java servlet is a program that executes on a server.

The Java Buzzwords

Title Description
Simple Java is easy to learn and use
Secure Java provides security
Portable Java programs can be execute in any environment
Object-Oriented Java embodies mordern Object-Oriented

Object-Oriented Programming

At the center of Java is object-oriented programming(OOP). The object-oriented methodology is inseparable from Java.

Java's

  • Encapsulation (Black Box) - is a programming mechanism that binds together and the data it manipulates, and that keeps both safe from outside interference and misuse.

The code and data consitute a class are called members or member variables/instance variables.

  • Polymorphism - from Greek, meaning "Many Forms" is the quality that allows on interface to access a general class of actions.

  • Inheritance - is the process by which one object can acquire the propertiesof another object.

The Java Development Kit

Before we can compile and run Java programs, we need a Java Development Kit(JDK). The JDK supplies two primary program. The first is javac, which is the Java compiler. The second is java, which is the standard Java Interpreter and is also referred to as the application launcher. JDK runs in Command-prompt.

The First Simple Program

  • In Java, a source file is officially called a compilation unit. It requires .java filename extension.

Compiling the Program

To compile the Example program, execute the compiler, javac, specifying the name of the source file on the command line.

javac Example.java

The javac compiler creates a file called Example.class that contains the bytecode. Bytecode must be executed by a Java Virtual Machine. Thus the output of javac is not a code that can be directly executed.

To actually run the program, we must use Java Interpreter, java. To do so, pass the class name Example as a command-line argument, as shown here:

java Example

Java line by line, comments are ignored by the compiler

  • *Variable is a named memory location that can be assigned a value. Further, the value of a variable can be change during the execution of the program.

Chapter 2 - Introducing Data Types and Operators

Why Data types are important? Data types are specially important in Java because it is a strongly typed language. This means that all operations are type-checked by the compiler for type compatibility.

Java Primitive Types

Java Primitive Types is used to indicate that these types are not objects in an object-oriented sense, but rather, normal binary values. For efficiency concern.

Java contains two general categories of built-in data types:

  • Object-oriented
  • non Object-oriented

Object Oriented types are defined by classes.

There are eigth primitive types or data types in Core Java:

Type Meaning
boolean Represents true/false values
byte 8-bit integer
char Character
double Double-precision floating point
float Single-precision floating point
int Integer
long Long integer
short Short integer

Java defines four integer types: byte,short,int, and long.

Hexadecimal, Octal, and Binary Literals The number system based on 8 is called octal, and it uses the digits o through 7. In octal the number 10 is the same as 8 in decimal. The base 16 number system is Hexadecimal and uses the digits o through 9 plus the letters A through F, which stand for 10,11,12,13,14, and 15.

  • A Hexadecimal literal must begin with ox or oX(a zero followed by an x or X)

  • An ocat literal begins with a zero.

hex = 0xFF;
oct = 011
Escape Sequence Description
\` Single Quote
\" Double Quote
\\ Backslash
\r Carraige return
\n New line
\f Form feed
\t Horizontal tab
\b Backspace
\ddd Octal constant
\uxxxx Hexadecimal constant

Variables

type var-name;

where type is the data type of the variable, and var-name is its name. You can declare a variable of any valid type, including the simple types just described, and every variable will have a type.

Initializng a Variable

type var = value;

Here, value is the value that is given to var when var is created. The value must be compatible with the specified type.

Operators

Java provides a rich operator environment. An operator is a symbol that tells the compiler to perform a specific mathematical or logical manipulation.

Java has four general classes of operators:

Arithmetic
Bitwise
Relational
Logical

Arithmetic Operators

Operator Meaning
  • | Additional (also unary plus)
  • | subtraction (also unary minus)
  • | Multiplication / | Division % | Modulus ++ | Increment -- | Decrement

Increment and Decrement

x = 10;
y = ++x;

y is equal to 11

x = 10;
y = x++;

y is equal to 10


### Relational and Logical Operators

Operator | Meaning
--- | ---
== | Equal to
!= | Not equal to
> | Greater than
< | Less than
>= | Greater than or Equal to
<= Less than or equal to