Author: techfox9

Notes (Part 2) from HeadFirst Java..

Sunday, May 8th, 2005 @ 12:50 am

  • — Some methods of class Object
    equals(), getClass(), hashCode(), toString().
  • — A way of thinking about superclasses vs interfaces:
    Superclasses implement types, interfaces implement roles.
  • — About the Constructor
    — It is used to initialize the state of a new object.
    — If none is written, the compiler will create a default one (with no args.)
    — If one is written (any one) the compiler will not supply the default one.
    .. ergo ..
    — If a no-arg one is wanted and there is at least another one, the default
    one must be written.
    — It is good to always supply a default one with default values.
    — Overloaded ones must have different arguments (just like any other method).
    — Argument list concept includes order and/or type of arguments.
    — If the nature of the class is such that the object MUST be initialized
    (such as the Color class), do not write a default one.
  • — Every constructor can call super() or this() but never both.
  • — To prevent a class from being instantiated into objects,
    mark the constructor ‘private’. For example, many ‘utility’
    classes have only ‘static’ methods and they should not be
  • — Finals..
    — A final variable cannot have its value changed.
    — A final method cannot be overriden.
    — A final class cannot be extended.
  • — Serialization..
    — Write object basic pattern:

    .. class SomeClass implements Serializable ..
    SomeClass sc = new SomeClass();
    try {
      FileOutputStream fs = new FileOutputStream("sc.ser");
      ObjectOutputStream oos = new ObjectOutputStream(fs);
    catch(Exception exc) {

    — If a variable in a ‘Serializable’ class cannot (or should not)
    be serialized, it must be marked ‘transient’.

    — Read object(s) basic pattern:

    FileInputStream fis = new FileInputStream("foo.ser");
    ObjectInputStream ois = new ObjectInputStream(fis);
    Object one = ois.readObject();
    Object two = ois.readObject();
    SomeClass sc = (SomeClass) one;
    SomeOtherClass soc = (SomeOtherClass) two;

    — Static variables are not serialized.

    — Class changes (versions) may break serialization.

  • — Java new IO (nio) features
    — IO performance improvements by using
    native IO facilities.
    — Direct control of buffers.
    — Non-blocking IO capabilities.
    — Existing ‘File[Input|Output]Stream classes
    use NIO internally. Some NIO features may be
    accessed via the ‘channels’.

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