Primitive Data Types

( http://docs.oracle.com/javase/tutorial/java/nutsandbolts/datatypes.html )




byte
short
int
long
float
double
boolean
char


uninitialized field will be set to a default value by the compiler.
but, uninitialized local variable will not be set to a default value by the compiler.
accessing an uninitialized local variable will result in a compile-time error!



// The number 26, in decimal
int decVal = 26;

//  The number 26, in hexadecimal
int hexVal = 0x1a;

// The number 26, in binary
int binVal = 0b11010;




null can be used as a value for any reference type.

class literal refers to the object that represents the type itself.
      ex) String.class

Package

package is a namespace that organizes a set of related classes and interfaces.

conceptually I can think of packages as being similar to different folders.




Java Platform, Standard Edition 7 API Specification

http://docs.oracle.com/javase/7/docs/api/index.html

Interface

interface

interface is a group of related methods with empty bodies.



implements keyword



public keyword to the implemented interface methods.

inheritance

inheritance 

superclass
subclass


one direct superclass
unlimited number of subclass


extends keyword

Lesson: A Closer Look at the "Hello World!" Application

( http://docs.oracle.com/javase/tutorial/getStarted/application/index.html )






public class HelloWorldApp {
public static void main(String[] args) {
System.out.println("Hello World!");
}
}

The Java language support three kinds of commnets:

/* text */

/** documentation */

// text

Every application begins with a class definition.

Every application must contain a main method whose signature is:

      public static void main(String[] args)