A.4 Objects

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	Building Parsers with Java By Steven  John  Metsker
	Table of Contents
	Appendix  A.   UML Twice Distilled

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An object diagram illustrates specific instances of classes, as Figure A.4 shows.

Figure A.4. Objects. The UML provides features for showing specific object structures and interactions.

In Figure A.4, note the following.

• An object typically appears as a colon followed by the name of the class, all underlined , in a rectangle. For example, :Repetition indicates an object of the Repetition class.

• A diagram can point out the name of a variable that references an object by prepending the name, as in good:Sequence .

• A line between objects indicates that one object has a reference to another.

• An object diagram can show the value of an instance variable, as with the :Literal objects in Figure A.4.

• A diagram can show a sequence of objects sending messages to other objects, as the lower part of Figure A.4 shows. The order of messages is top to bottom, and the dashed lines indicate the existence of the object over time.

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