{"id":4542,"date":"2012-12-14T22:00:57","date_gmt":"2012-12-14T20:00:57","guid":{"rendered":"http:\/\/www.javacodegeeks.com\/?p=4542"},"modified":"2012-12-14T20:41:53","modified_gmt":"2012-12-14T18:41:53","slug":"google-guava-bimaps","status":"publish","type":"post","link":"https:\/\/www.javacodegeeks.com\/2012\/12\/google-guava-bimaps.html","title":{"rendered":"Google Guava BiMaps"},"content":{"rendered":"

Next up on my tour of Guava<\/a>, is the BiMap<\/a>, another useful collection type. It’s pretty simple really, a BiMap is simply a two way map.<\/p>\n

Inverting a Map<\/h2>\n

A normal java map is a set of keys and values, and you can look up values by key, very useful, eg lets say I wanted to create a (very rudimentary) British English to American English dictionary:
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\n <\/p>\n

Map<String,String> britishToAmerican = Maps.newHashMap();\r\nbritishToAmerican.put('aubergine','egglant');\r\nbritishToAmerican.put('courgette','zucchini');\r\nbritishToAmerican.put('jam','jelly');<\/pre>\n
But what if you want an American to British dictionary? Well you could write some code to invert the map:<\/p>\n
    \/\/ Generic method to reverse map.\r\n    public %lt;S,T> Map<T,S> getInverseMap(Map<S,T> map) {\r\n  Map<T,S> inverseMap = new HashMap<T,S>();\r\n  for(Entry<S,T> entry: map.entrySet()) {\r\n   inverseMap.put(entry.getValue(), entry.getKey());\r\n  }\r\n  return inverseMap;\r\n }<\/pre>\n
It’ll do the job, but there’s several complications you might need to think about.<\/p>\n