class attribute Attributes of a class that are shared by all in Java

Printing ECC200 in Java class attribute Attributes of a class that are shared by all
class attribute Attributes of a class that are shared by all
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instances of the class There will be only one copy of each class attribute, and it is possible to access these class attributes without creating any instances of the class These are sometimes called static attributes in Java
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class method A method defined by a class that only operates
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on class attributes Class methods can be used without creating any instances of the class These are sometimes called static methods in Java
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instance attribute An attribute of a class that is associated with
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a particular instance of the class Each instance will have its own copies of instance attributes
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instance method Methods defined by a class that operate on
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instance attributes This is the most common type of method defined by a class, and an instance method will be used only with its associated instance of the class
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Accessing Objects Object-oriented languages provide the basic mechanisms needed to access the various parts of an object But just as convention calls for setters and getters, there are other special cases for accessing the attributes and methods of an object that have their own terminology The following definitions cover the basic terms used to describe different kinds of object access
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container A class whose instances are collections of other
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objects These collections may be objects all of the same type, or of mixed types, although they usually have a common superclass Containers include lists, stacks, queues, bags, and others They usually provide a method to iterate over each object in the container
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iterator An iterator is a method (or methods) used to access or
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visit each part of an object This allows the outside world controlled access to all important parts of an object without the need to know the internal implementation details of a specific object Iterators are often used with container classes, and typically work by accessing the first item in a container, and then each subsequent object until all objects have been accessed
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mix-in A class (or usually an interface in Java) that is used to
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define a single behavior Mix-ins are usually not standalone classes, but are used to provide a standard for implementing the designed behavior
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callback A method that is called when an event has taken
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place Usually used in association with a listener When a listener detects an event, it will invoke the callback of objects that need to know that the event has occurred
listener A method that responds to events These are usually
system events such as mouse clicks or timer events The listener will typically invoke callbacks of objects that need to respond to the event
link A reference to another class Used to build associations
between classes
this Also called self A reference to the current object Within a
class definition, references to the attributes and methods of the class are implicit The this reference can be used for clarity to make a reference explicit Most commonly, however, this is used to pass a reference to the current instance to another object It can also be used to set a class variable to refer to specific instance of the class
A Low-Level View of Objects At some point while a programming is running, class instances must have some low-level implementation in the memory of a computer Having an understanding of how objects can be implemented at this low-level can help you understand just what is going on The UML representation of an object with the separate attribute and operation fields is in fact a reasonable model of how objects are represented in memory There are really two main components of any
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object: the data or attributes, and the code that implements the methods We will discuss the code part first A class definition includes the code for all methods of a class The compiler will translate the high level Java code into low-level Java Virtual Machine code This is the code that runs on each computer Because every instance of a class will use the same methods, there really needs to be only one copy of each method defined by a class There does not need to be a separate copy for each object instance This is true for both instance and class methods and attributes So, for each class, there will be a single copy of all the code for the methods, as well as the storage for any class attributes On the other hand, the instance data associated with each object will be unique to each instance of a class Each object exists as a separate entity with its own identity Thus, when an object is first created with a new operator, Java will dynamically create the storage space required for the instance attributes Because this dynamic storage must be initialized, most object-oriented languages, including Java, will invoke a special class method called the constructor whenever an object is first created Java will create new objects only with by an explicit use of the new operator It never automatically creates new objects Since only class methods (static methods) can be invoked without creating an instance of a class, your program's main entry point is the class method static void main Java will automatically create temporary storage for primitive items like ints as well as object references This storage is created to hold the parameters passed when a method is called Most implementations of Java will use four different areas of memory to store these various items First, there will be two areas of
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