Java Collections

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Java Collections

• Gary Greer

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How Will You Store Data?

• one of the big programming decisions is in how
  you will store data
• often you will not know how much data you will
  need to store, so an array just wont cut it
• also there is often a lot of programming that
  revolves around storing and retrieving data
• Collections can solve these problems

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What Are Collections?

• Collections are classes which store information
• may also be called containers
• they are Java objects
• can be used in programs by importing java.util.
• they have been written by experts

This presentation refers a great deal to
information from Eckel, 2003.
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Collections Advantages

• no pre-defined limit on the size of the
  collection (as big as you want)
• much of the programming is already done
• they are generally fast and efficient
• all collections have a similar interface so once
  you use one, using another is easy
• you will save writing time

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Collections Disadvantages

• if you have a program where speed is crucial,
  collections may not be quick enough
• a collection can contain only objects
• if you need to store primitives (like integers)
  you need to wrap them in a wrapper class (like
  Integer)
• a collection does not know what type of object it
  contains and the programmer needs to cast the
  object into the correct type

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Collections 2 Basic Types

• true collections provide places to hold
  individual elements
• these can be lists or sets
• examples are ArrayList and TreeSet
• maps are special in that they hold keyelement
  pairs
• imagine a structure for example which holds words
  and the associated definitions
• an example is a TreeMap

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Sounds Difficult!

• well, it is not that difficult really
• there is really minimal programming involved,
  although there are a few things to be learned
• however, unlimited size and faster program
  writing are usually worth it

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References

• Eckel, B. (2003). Thinking in Java. Retrieved
  from www.BruceEckel.com
• Sun MicroSystems (2005). Java APIs. Retrieved
  from http//java.sun.com/j2se/1.5.0/docs/api/index
  .html