Java OOP Language

Java OOP Language

1. Class

   • Object
     • Fields
       • AKA: Attributes or Variables
     • Methods
       • AKA: Actions or Functions
         • Method and Field Names: camelNamingConvention
         • returnType methodName (listOfArguments)
         • Main is a special method that only has to be in one class. This method allows the class containing it to be invoked.
       • returnType methodName (listOfArguments)
       • Return Type of a Method can be a Primitive, an Object, or Void
         • Primitive Data Types include: the boolean, byte, char, short, int, long, float, and double
           • A value with two choices: true or false
           • An 8-bit signed two's complement integer, that has a minimum value of -128 and a maximum value of 127 (inclusive)
           • A single character enclosed in single quote marks like this: char myCharacter = 'g'
           • A 32-bit signed two's complement integer, which has a minimum value of 2^-31 and a maximum value of 2^31
             • An Integer
           • A 64-bit two's complement integer, which has a minimum value of -263 and a maximum value of 263^-1
           • A 16-bit signed two's complement integer, that has a minimum value of -32,768 and a maximum value of 32,767 (inclusive)
           • A double type variable is a 64-bit floating data type which can represent fractional as well as whole values. Contains up to 15 digits in total, including those before and after the decimal point.
           • The float data type is a single-precision 32-bit IEEE 754 floating point which has an unlimited value range. It should never be used for precise values, such as currency.
         • The return type Void means that the method returns nothing
     • AKA: Instances
     • To create an object use "new" followed by the constructor of the class to be instantiated
     • To call a method or access a field use "objectReference.methodName" and "objectReference.fieldName"
     • A Reference Variable refers to an object
       • Reference Variables with no value have a "null" value
       • To test if a Reference Variable is null, use the "==" operator
   • Class Names: PascalNamingConvention
   • class className { [class body] }
   • Constructor
     • Sometimes called a constructor method (looks like a method)
     • No return value, not even void
     • Must have same name as class
     • constructorName (listOfArguments) { [constructor body] }
     • Constructor Arguments can be used to initialize fields in Objects