4.6 Week 6 - OOP -- Java Object Terminology

4.6 Week 6 - OOP -- Java Object Terminology

4.6.1 Reading and Web Sites

1. re-reading van der Linden Chapter 2, The Story of O, Object Oriented Programming
2. re-reading van der Linden Chapter 6, More OOP -- Extending Classes

4.6.2 Notes

1. class
   1. Basic building block of a Java^TM program.
   2. Can contain methods.
   3. Can contain variables.
   4. Can contain constructors.
   5. Can contain initialization code that is run when the class is loaded.
   6. Is the blueprint for making class instances/objects.
   7. Can contain other classes.
   8. Should be reusable.
   9. Interface should be simple.
   10. Avoid public variables. Use set and get methods.
2. objects
   1. I think of an object as:
      1. The public methods to manipulate the hidden data.
      2. static (one only data - in class, not object).
      3. non-static data, one set for each instance.
      4. An object or instance is created with new.
      5. Contains a "pointer" to its class and all of its methods.
   2. Sometimes called an instance.
3. method signature
   The specific order and type of the calling arguments and implementation parameters of a method. Having multiple signatures is how a method is overloaded.
4. method subsumption
   What happens when a type is "promoted" prior to the call to the method.
5. field
   The name of data in an object. It is stored on the heap. The memory is allocated when the object is instaintiated with new.
6. inheritance
   1. All classes but Object inherit from a superclass.
   2. inheritance includes all methods and variables, static and non-static.
   3. inheritance excludes all private members.
   4. method signatures and variable names can be overridden. Visibility is to the "innermost" class or block.
   5. All super constructors are called PRIOR to calling the subclass constructor.
   6. An overridden method or variable can be referenced using the keyword super.
   7. Java^TM allows only single inheritance. C++ uses multiple inheritance. The "same" result can be implemented in most cases using an interface.
7. method
   1. I think of a Java^TM method as a C function.
   2. In Java^TM all methods of the same name MUST return the same type.
   3. A method signature is the specific type and order of calling arguments.
   4. Multiple method signatures is method overloading.
   5. Java^TM does NOT permit variable argument lists like C and C++.
   6. A method of one signature can call a method with a different signature in the same class.
8. constructors
   1. Does NOT have a return type. It returns a reference to the newly created instance.
   2. Must have the same name as the class.
   3. Can be overloaded with multiple signatures.
   4. "Should" be placed at the top of the class.
9. override
   If a subclass has a method with the same name and signature of a super class, the superclass method is being overridden.
10. superclass
    The class that a subclass inherits from.
11. interface / implements
    1. An interface describes a public set of methods that must exist in a class that implements the interface.
    2. A class that implements an interface must implement all of the variables and method signatures that are contained in an interface.
    3. Allows a class to implement/be a certain "type" of class without inheritance.
    4. A new class can only extend one class.
12. overloading
    Having multiple signatures so that when a method is called with a specific set of argument types the compiler makes sure that the right method is called.
13. static van der Lindenp55. (Version 4. p56)
    1. A static method does NOT take a reference
    2. static item occur only once.
    3. static public void main(String args[]) must be static.
14. non-static
    1. A method that takes a reference. reference.method-name(argument-list)
    2. A variable that has been instantiated.
    3. Perhaps an "object" or an "instance".
15. instantiate
    1. Using new to call a constructor.
16. object destruction
    1. Think of it as an automatic call to free in C.
    2. Handled by the Java^TM garbage collector.
    3. Occurs when there are no outstanding references to an instance.
17. reference
    1. What Java^TM returns from a constructor.
    2. Used with non-static object or instances
    3. Think of C pointers.
    4. Are dereferenced automatically. No * operator.
18. dereference
    Happens in Java^TM automatically. This results in a LOT less segmentation violations or seg faults. <grin>.
19. primitive types
    1. What the compiler / JVM really understands.

    Precision	Primitive Type
    true/false boolean	boolean
    8 bits signed integer	byte
    16 bits unsigned integer	char
    16 bits signed integer	short
    32 bits signed integer	int
    64 bits signed integer	long
    32 bit floating point	float
    64 bit floating point	double

20. wrapper types
    1. Creates a object for each of the primitive types.
    2. Has many "useful" methods associated with each one.

    Precision	Primitive Type	Wrapper Object
    true/false boolean	boolean	Boolean
    8 bits signed integer	byte	Byte
    16 bits unsigned integer	char	Character
    16 bits signed integer	short	Short
    32 bits signed integer	int	Integer
    64 bits signed integer	long	Long
    32 bit floating point	float	Float
    64 bit floating point	double	Double

21. this reference
    Lets you reference a class variable instead of the method variable.
22. super reference
    Lets you call a super method rather than the current class method.
23. visibility
    If you use the same name, what variable or method is being referenced? The answer is the "closest" one (with the correct signature).
24. package
    1. Organize a set of classes.
    2. Organized hierarchical manner.
    3. Can contain other packages
25. public
    Can be referenced outside of the class.
26. private
    Can only be referenced within the class.
27. protected
    Members are accessible in package and in subclasses of the class.

4.6.3 Lab Assignment - None

4.6 Week 6 - OOP -- Java Object Terminology