Java 天地·Core Java·Lecture Notes·Unit 1- Object Concepts & Java

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Messages with arguments

Many operations are designed to be as general purpose as possible. One way this is achieved is by having an operation that can change what it does according to some values passed to it along as part of a message. For example, an operation to increase the balance of a bank account would probably be designed to expect a particular value of how much to deposit. The sending of such a message might be in the form:

send message depositMoney( 101.54 ) to object bankAccount123

In the above example a particular object (bank account number 123) is to be credited with ?01.54. The value "101.54" is called an argument (also sometime called a parameter). Messages can include zero, one or many arguments. Other example of possible message with arguments include:

send message setRadius( 200 ) to object circle1

send message setWindowPosition( 100, 200 ) to object notepadApplication1

send message retrieveHTMLPage("www.mdx.ac.uk/index.HTML") to object browserWindow2

You actually have a lot of experience of sending messages with arguments through your interaction with almost all Windows programs. For example, In a text editor or word processor when you wish to save a file with a new name and select the ‘Save File As’ menu choice, you are presented with a dialog window in which you enter/choose the file name and location. The dialog window object will then send a message with your choices (as arguments) back to the application, and the application will write the file to disk. In the figure below a file is being saved from the Notepad accessory application:

image31.gif (4364 bytes)

A reply such as the following is returned to the application from this file dialogue object:

return to object notepadApplication1
the reply ["c:\temp\", "menu1", textDocument]

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