java foundation 1

Java is an interpreted language {introduction, efficient, cross-platform (write once run anywhere)}java virtual machine>java compiler>bytecode file---*.class----class loader

Is a pure object-oriented language {encapsulation inheritance polymorphism}

James Gosling (1990 Written Language (oak--oak))

1995 improved to form java----jdk1.0

Identifiers
    Anything you need to name yourself is called an identifier

Code specification:
    1. Identifiers can be composed of letters (both upper and lower case), _, $, and cannot start with numbers

   2. All variable and method declarations must be well-known

    3. CamelCase (the first letter of the first word is lowercase, the rest of the words are capitalized)
       getElementById()
   4. Spaces must be left on both sides of any operator

   5. The first letter of the class name must be capitalized

Java basic data types:

Four types and eight types (basic data types):
integer type
            byte 2 to the 8th power occupies 1 byte
            short 2 to the 16th power occupies 2 bytes
            int 2 to the 32nd power occupies 4 bytes
            long 2 64 times Square occupies 8 bytes

Floating point
            float 7 bits of significand 4 bytes
            double 16 bits of significand 8 bytes

 boolean
            boolean true / false 1 byte
character
            char 0 - 65535 2 bytes

    string (not of data type)
        String

Reference types:
        all classes,
        all interfaces
        , all arrays,
        null