TreeMap Tutorials

From Progzoo

Revision as of 20:24, 12 September 2012 by 08014201 (Talk | contribs)

A TreeMap relates keys to values. Often the keys are Strings and the values are more complex objects.

  • In these examples, the TreeMap world is of type TreeMap<String,Country>.
  • The data is read from a text file http://progzoo.net/bbc.txt
  • The key value is the name of a country, the value in each case is an object representing the country:
world
KeyValue
Afghanistan(name:'Afghanistan',region:'Asia',area:652225sqkm,pop:26000000,gdp:0)
Albania(name:'Albania',region:'Europe',area:28728sqkm,pop:3200000,gdp:6656000000)
Algeria(name:'Algeria',region:'Middle East',area:2400000sqkm,pop:32900000,gdp:75012000000)
Andorra(name:'Andorra',region:'Europe',area:468sqkm,pop:64000,gdp:0)
Angola(name:'Angola',region:'Africa',area:1250000sqkm,pop:14500000,gdp:14935000000)
...
Zambia(name:'Zambia',region:'Africa',area:752614sqkm,pop:11000000,gdp:4950000000)
Zimbabwe(name:'Zimbabwe',region:'Africa',area:390759sqkm,pop:12900000,gdp:6192000000)

Contents

Access a value: get

You can access a specific value using get

If you know the name of a country (the key) you can access the associated value.

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Missing keys: get

If you try to get a key that is missing it will return null.

The null object is returned of the value is missing.

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Testing keys: containsKey

You can check to see if a key exists using containsKey

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Adding an entry: put

You can create a new entry using put. You must give the key and the value.

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Iterating over the keys: keySet()

You can run over all of the keys using the keySet() method.

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Iterating over the values: values()

You can run over all of the values using the values() method.

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