Ignore case while comparing string with keyvalue in the hashmap

Question

I am trying to check if my hashmap key set contains the string 'buffSB.toString()'. But I wanted to compare ignoring case (upper or lower).

static StringBuilder buffSB = new StringBuilder(); 

buffSB.append(alphabet);

Map<String, String> pref =  new Datamatch().main();  // Getting the Hashmap from other class

if(pref.containsKey(buffSB.toString()))             //This is where I need to ignore case while searching string in the map key set 
  { 
      String val = pref.get(buffSB.toString());
  }

Any help will be greatly appreciated!!!

Community · Accepted Answer · 2017-05-23 11:59:20Z

3

You can also try to use TreeMap which enable providing a comparator to its constructor:

Map<String, String> yourMap= new TreeMap<String, String>(String.CASE_INSENSITIVE_ORDER);

see Case insensitive string as HashMap key

edited May 23, 2017 at 11:59

CommunityBot

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answered Nov 20, 2015 at 14:49

jMounir

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Comments

Yogendra Joshi · Accepted Answer · 2015-11-23 07:39:48Z

2

If you see the implementation of HashMap getKey method you have to pass the proper key to generate the hash value and get the actual value from that bucket.

    if (key == null)
        return getForNullKey();
    int hash = hash(key.hashCode());
    for (Entry<K,V> e = table[indexFor(hash, table.length)];
         e != null;
         e = e.next) {
        Object k;
        if (e.hash == hash && ((k = e.key) == key || key.equals(k)))
            return e.value;
    }
    return null;

Three solutions

    Map<String, String> pref = new TreeMap<String, String>(String.CASE_INSENSITIVE_ORDER);

OR

    Map<String, String> map = new CaseInsensitiveMap<String, String>();

OR

    Looping through map with the ignore case

edited Nov 23, 2015 at 7:39

answered Nov 23, 2015 at 7:33

Yogendra Joshi

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Comments

Jean Logeart · Accepted Answer · 2015-11-20 14:38:22Z

2

Only use lowercase keys:

map.put(key.toLowercase(), value);
// later
String val = map.get(someKey.toLowerCase());

answered Nov 20, 2015 at 14:38

Jean Logeart

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2 Comments

Yassin Hajaj Over a year ago

And if he absolutely needs the strings to have Uppercases and Lowercases? Like names for example...

philwalk Over a year ago

this has the benefit of avoiding duplicate keys that differ only by case.

Lipsyor · Accepted Answer · 2015-11-22 17:30:13Z

You may use CaseInsensitiveMap<K,V> instead of Map<K,V>

It extends AbstractHashedMap<K,V> and it ignores case of keys. You can create a new instance of this map by passing the existing case-sensitive map to the constructor.

Consider this example:

Map<String, String> map = new CaseInsensitiveMap<String, String>();
map.put("One", "One");
map.put("Two", "Two");
map.put(null, "Three");
map.put("one", "Four");

The map will contains three elements:

<one, "Four">
<two, "Two">
<null, "Three">

Infact map.put("one", "Four") overwrites the value insert with map.put("One", "One").

map.get(null) returns "Three".

map.get("ONE"), map.get("one"), map.get("One"), and so on returns "Four".

Keep in mind that the keySet() method returns all lowercase keys, or nulls.

keySet() equals {"one", "two", null}.

Further documentation

Bon · Accepted Answer · 2015-11-20 14:38:33Z

1

You can loop through the keySet of the map, for each key, use the string function equalsIgnoreCase to compare:

    Map<String, String> pref = new Datamatch().main();  // Getting the Hashmap from other class

    String val;
    for (String key : pref.keySet()) {
        if (key.equalsIgnoreCase(buffSB.toString())) {
            val = pref.get(key);
            break;
        }
    }

answered Nov 20, 2015 at 14:38

Bon

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Comments

Steven · Accepted Answer · 2015-11-20 14:35:00Z

-1

pref.containsKey(buffSB.toString().toLowerCase())

Use string.toUpperCase() or string.toLowerCase() to ignore case.

answered Nov 20, 2015 at 14:35

Steven

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1 Comment

nano_nano Over a year ago

if pref contains "Hello". what would be the result for "HELLO" or "hello"?

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