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Objects, Classes, and Events

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this

Each time an object is instantiated, apointer is created in the stack to theobject, which resides in the heap

A copy of the pointer is given toanything that instantiates the objectusing the new keyword

When a method that belongs to anobject is in scope, a copy of thepointer to the object itself is put inthe stack and is available via code

using the this keyword.

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static

static classes and values exist only as asingle instance, unlike objects.

Static methods can only access static items,

and never use this, since there is no instanceas far as they are concerned.

The data is stored in the method area,which belongs to the JVM.

You can use these in your classes when youonly need a single item (method, property)across all instances

When the JVM is reset, so are static properties

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static

What are some good examples weve

seen/used this quarter?

Example

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interface

Interfaces are a contract of publicproperties and methods

A class that implements a giveninterface must include methods thatfulfill the contract

The purpose is so that users of a

given class can use an interface theyneed without knowledge of all of thedifferent classes that implement it

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interface

Example

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Event-Driven programming

How do GUI interfaces such asWindows and OSX differ fromprocedural interfaces such as a

command line? How many events can a user cause?

Using Javas awt package, it is

possible to writeevent listeners

that perform a given method when agiven event occurs

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ActionListener interface

This is one of many interfaces used tohandle events

It declares an actionPerformed()method that takes in an ActionEventobject.

You can write classes that implement

this interface. This will allow you writeyour own event handlers.

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ActionListener and JButton

To add an event to a JButton, simplyuse the objects addActionListenermethod

Pass in an instance of your class thatimplements ActionListener

When the button is clicked, the

ActionListner objectsactionPerformed method will betriggered

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Nested Classes

Nested classes are classes that aredefined within a class

This means you can have a class thatdoes not have its own .java file

When compiled, the inner class willhave its own .class file created

These are used when the class is onlyuseful to the outer class

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Nested Classes

Inner Class (aka Member class): a classdefined within a class. It has access to allmembers of the class that defined it.

Nested Static Class: An inner class with thestatic keyword. Everything in it andeverything it accesses is static

Local Class: A class defined within a block

of code of another class. It has access to allmembers in the class that defined it.

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Anonymous Inner Classes

These are defined inside anotherclass and not assigned a referencename

Mostly used for writing eventhandlers

Discuss example