Tom's Programming Blog: BiMaps

BiMaps

Well, guess what? This is the sort of situation a BiMap is designed for! And here's how you might use it.

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BiMap<String,String> britishToAmerican = HashBiMap.create();   // Initialise and use just like a normal map britishToAmerican.put("aubergine","egglant"); britishToAmerican.put("courgette","zucchini"); britishToAmerican.put("jam","jelly");   System.out.println(britishToAmerican.get("aubergine")); // eggplant   BiMap<String,String> americanToBritish = britishToAmerican.inverse();   System.out.println(americanToBritish.get("eggplant")); // aubergine System.out.println(americanToBritish.get("zucchini")); // courgette

Pretty simple really, but there's a few things to notice.

Enforcing uniqueness

Firstly the BiMap enforces uniqueness of it's values, and will give you an illegal argument exception if you try to insert a duplicate value, ie

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1 2	britishToAmerican.put("pudding","dessert"); britishToAmerican.put("sweet","dessert"); // IllegalArgumentException.

If you need to add a values that has already been added there's a forcePut method that will overwrite the entry with the duplicate value.

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britishToAmerican.put("pudding","dessert"); britishToAmerican.forcePut("sweet","dessert");  // Overwrites the previous entry System.out.println(britishToAmerican.get("sweet")); // dessert System.out.println(britishToAmerican.get("pudding")); // null

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