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Computer programming is the process that automates computer software. Most computer programs store digital data in files. A hash table is a special table made up of key value pairs, which is generated for performance reasons. The hashtable key is the method of accessing a specific piece of information from a hashtable. The key is the searching parameter that is used to access a specific value from a data file.
Typically a hashtable is a table full of keys value pairs. With this technique each value has a corresponding hashtable key. This type of table can be used in many functional areas of computer processing. The table is considered a data structure, which uses a hash function to access the hashtable key within the table. The hash function converts plain-text data into hash keys, for the purpose of data access.
When data is stored in data files, computer programs are created to retrieve the data. Hash functions typically have faster access algorithms than normal plan-text searches. This is because a hashtable key is a binary representation of the original data, which provides better performing indexes for searching.
A hashmap is an unsynchronized version of a hashtable. It contains a list of key value pairs that are randomly ordered. The hashmap allows the creation of null values within the table, which is not available with a normal hashtable. These null values may be necessary for some business functions.
Hashtables use hashing algorithms to create the hashtable key. These algorithms are mathematical functions that convert plan-text data into a numerical representation. Each hashing algorithm has a specific approach to creating the hashed key. Some algorithms have better performance characteristics but suffer from data integrity problems.
One of the drawbacks to hashing algorithms is the issue of hashing collisions. A collision occurs when two plain-text values of data compute to the same hashed value. This is typically unavoidable when dealing with large data sets because eventually a collision will occur. There are several collision resolution techniques that are used for hashtables. Each technique attempts to address the issues of collision in a specific manner.
Separate chaining is an example of a hashtable collision deterrent. This process requires the creation of a list of key value pairs that have collided within the hashtable. The separate link list tracks all collisions. It is used by the hashing algorithm as an additional searching table. Typically the separate chaining resolution is sufficient for most hashtable configurations.