Basics of Defining and Using Classes

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Basics of Defining and Using Classes

• Chapter 5, Review

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5.2.1 Designing Classes

• Default values for the primitive and reference
  data types
• Long 0
• Object reference null
• Char \u0000
• Float 0.0

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5.3.2 Variables

• There is the storage of local or method data, the
  storage of object data and the storage of class
  data.
• All objects are created in RAM. The area of
  storage that is used is referred to as the heap
  storage.
• All method data are also created in RAM. That
  area is called stack storage.
• All class data are also created in RAM. The area
  of storage that is used is referred to as the
  static storage.

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5.3.3 Instance Variables

• When one object stores the reference to another
  object, it is described as having a reference.
  This relationship between the two objects is also
  referred to as a "has a" relationship. This means
  that an association between the two objects
  exists through the reference data.

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5.3.4 Class data and Static Variables

• Variables that are associated with a class and
  are shared by all objects of the class are known
  as class or static variables.
• Class variables are created and initialized when
  that class is loaded by the JVM.
• If the value of the class variable is changed,
  then the new value is available to all objects.

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5.4.1 The concept of encapsulation

• Data is kept private.

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5.4.2 Access modifiers

• Data that is final yet accessible outside the
  object should be declared public
• The best way to declare a Class available to
  everyone is
• public class Porcupine ()

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5.6.1Method Syntax

• The method can be understood in terms of three
  sections or parts  
• The method identifier elements, which include
  modifiers, qualifiers, return-type, and name
• The method arguments, which include data-types
  received by the method defined inside the
  parentheses ( )
• The method body defined inside opening and
  closing braces

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5.6.1Method Syntax

• The method syntax includes several required
  elements. These include
• the return-type
• the method-name.

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5.6.4 Return value

• In all instances, the data type of the values
  must be assignment compatible to the data-type
  declared as the return type in the method
  definition.

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5.6.6 Concept of pass-by-value

• A reference passed in as an argument cannot be
  changed to refer to another object.

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5.6.7 Main Method

• Syntax requirements
• Access modifier public
• Variable to store argument data named args
• The qualifier static
• Return type void

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5.6.8 Instance methods

• Methods that can only be accessed through an
  object of a class are known as instance methods.
• If the qualifier static is not declared in the
  method definition, the method is considered an
  instance method.
• Instance methods can also access non-private
  methods and variables of other classes.

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5.6.9 Class Methods

• Class methods require that no objects of the
  class be created in order to use these methods.
• Instance variables and non-static methods cannot
  be directly accessed by static methods of the
  same class.
• The main method is a static method.
• Class methods are also known as static methods.

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5.9.1 Overloading methods

• Methods are typically overloaded because the user
  wants to have different versions of a method
  accept different input, but have the same name
  since they have similar functions.
• Example
• Int DoNothing( double LazyA)
• Int DoNothing( float LazyA)

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5.9.1 Initializing data

• A static block is used to initialize static
  variables of a class. This block is executed only
  once when the class is loaded at run time. The
  static block is defined using the keyword static.
  This block can only initialize static variables
  of the class.

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5.9.6 Destruction of an object

• The value of a reference variable can be reset to
  null. The variable no longer refers to an object.
  The object it originally referenced will be
  destroyed if no more references to it exist.

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5.10.3 Lifetime of an object

• The lifetime of an object or method variable in
  Java is the duration of the defining code block.

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5.10.5 Destruction of an Object

• The value of a reference variable can be reset to
  null.
• The variable no longer refers to an object.
• The object it originally referenced to will be
  destroyed if no more references to it exist. This
  typically occurs by the following line of code.