Difference between HashMap and HashTable
Main Difference
HashMap and HashTable are the two critical data structures in Java. They are in the framework of the collection and have little in common between the two. Although they have these similarities, there are some differences between them. Both HashMap and HashTables store data in the form of key-value pairs and only implement the Map interface. To store the elements, the Hashing technique is being used by both HashMap and HashTable. Since we have to address the differences between the two, the most important difference is based on thread safety. The main points of difference between HashMap and HashTable include null keys, iteration values, and synchronization. Performance and class.HashTable is thread-safe while HashMap on the other hand is not thread-safe. HashTable is internally synchronized, while HashMap is not internally synchronized, so HashMap is not safe to use in multi-threaded applications. HashMap performance is good compared to HashTable as HashTable is internally synchronized. HashMap is preferred over HashTable as HashTable is a legacy class and is considered to be due to deprecation. HashMap is fast compared to HashTable. Since the start of introduction of HashMap in JDK 1.2, it is a member of Java Collection Framework, but before JDK 1.2 HashTable is already there and by JDK 1.2 it has been made to implement Map interface and become a member of the Collection Framework. HashMap is preferred over HashTable as HashTable is a legacy class and is considered to be due to deprecation. HashMap is fast compared to HashTable. Since the beginning of introduction of HashMap in JDK 1.2, it is member of Java Collection Framework, but before JDK 1.2 HashTable is already there and by JDK 1.2 it has been made to implement Map interface and become member of Collection Framework. prefer HashMap over HashTable, since HashTable is an inherited class and is considered to be due to deprecation. HashMap is fast compared to HashTable. Since the beginning of the introduction of HashMap in JDK 1.2, it is a member of the Java Collection Framework, but before JDK 1.2 HashTable is already there and by JDK 1.2 it has been made to implement the Map interface and become a member of the Collection Framework. 2 has been made to implement the Map interface and become a member of the Collection Framework. HashMap is preferred over HashTable, as HashTable is a legacy class and is considered to be due to deprecation. HashMap is fast compared to HashTable. Since the beginning of the introduction of HashMap in JDK 1.2, it is a member of the Java Collection Framework, but before JDK 1.2 HashTable is already there and by JDK 1.2 it has been made to implement the Map interface and become a member of the Collection Framework. 2 has been made to implement the Map interface and become a member of the Collection Framework. HashMap is preferred over HashTable, as HashTable is a legacy class and is considered to be due to deprecation. HashMap is fast compared to HashTable. Since the beginning of the introduction of HashMap in JDK 1.2, it is a member of the Java Collection Framework, but before JDK 1.2 HashTable is already there and by JDK 1.2 it has been made to implement the Map interface and become a member of the Collection Framework.
Comparison chart
| HashMap | hash table | |
| Definition | HashMap allows a maximum of one null key and any number of null values are also allowed. | It does not allow a single null key nor the null value. |
| Return | To traverse the elements, HashMap returns only iterators | The returns are not only the iterators but also the enumeration. |
| Implementation | implements the Map interface by extending the AbstractMap class | Implement the Map interface by extending the Dictionary class. |
| Sync up | not internally synced | It’s synced internally |
Definition of HashMap
HashMap is the important data structure in the Collection Framework in Java. HashMap is not thread-safe it is not internally synchronized, so HashMap is not safe to use in multi-threaded applications. But you can make it safe for multi-threaded applications by synchronizing it externally using the Collections.synchronized() method. Implement the Map interface by extending the AbstractMap class. HashMap allows a maximum of one null key and any number of null values are also allowed. The iterators returned by HasMap are fast by nature. HashMap performance is good and thus it is fast compared to HashTable.
Definition of HashTable
HashTable is the important data structure in the Collection Framework in Java. HashTable is thread-safe and internally synchronized. Therefore, it is safe to use for multi-threaded applications. Implement the Map interface by extending the Dictionary class. It does not allow a single null key nor the null value. HashTable is a legacy class and is considered due to deprecation. The enumeration returned by HashTable is fail-safe in nature.
Differences in a nutshell
- HashTable is thread-safe while HashMap on the other hand is not thread-safe.
- HashTable is internally synchronized, while HashMap is not internally synchronized.
- Both HashMap and HashTable implement the Map interface, but they both extend different classes. HashMap implements Map interface by extending AbstractMap class while on the other hand HashTable implements Map interface by extending Dictionary class.
- HashMap allows a maximum of one null key and any number of null values are also allowed, while HashTable does not allow a single null key or the null value.
- To traverse the elements, HashMap returns only iterators while on the other hand, HashTable returns not only the iterators but also the enumeration.
- The iterators returned by HasMap are failsafe in nature, while the enumeration returned by HashTable is failsafe in nature.
- HashMap is faster than HashTable.
- HashTable is slow compared to HashMap.
- HashMap performance is good compared to HashTable as HashTable is internally synchronized.
- HashMap is preferred over HashTable, as HashTable is a legacy class and is considered to be deprecated.
- Since the beginning of the introduction of HashMap in JDK 1.2, it is a member of the Java Collection Framework, but before JDK 1.2, the HashTable is already there and by the JDK 1.2 it has been made to implement the Map interface and become a member of the Collection Framework.
