how to search like LIKe operator in sql in hash map in java

Question

I want to search a hash map depending on the user input. Suppose a user give value 'A',I have to display starting with A company name and if user give value 'AB' I have to display starting with AB company name. I am storing company name in hash map

Answer 1

1. Use a NavigableSet.

   Example:

   NavigableSet<String> company=new TreeSet<String>(); 
   Set<String> filteredSet=company.tailSet(prefix);
   for(String str:filteredSet) {
    if(str.startsWith(prefix))
     //add to list
    else
     break;
   }
   

2. Use a radix tree [wiki] or trie [wiki] if you are concerned about performance.The radix tree is more memory efficient compared to a trie.

Answer 2

Hash maps are only really good at finding exact matches based on some idea of equality which can be appropriately hashed.

Two options:

• Just go with a list instead, and search it linearly. For relatively small amounts of data, this is likely to work absolutely fine.
• Find or implement a trie (or prefix tree) which will basically start at a root node and descend for each character the user has typed - the results are all "valid endpoint" nodes below the node reached at the end of descending the user input.