Differences: HashTable Vs HashMap

HashTable Vs HashMap

• Hashtable is synchronized and thread-safe.HashMap is asynchronized and faster.
• HashMap implements Map interface.By using the Map interface it can switched between TreeMap &HashMap.
• HashMap permits the null values as key or value but Hashtable does not.
• HashMap does not guaranteed to store the values in a constant order over a period of time.
• Synchronization can be achieved by the HashMap by using java.util.collections.synchronizedMap(yourHashMap).This feature is added in JDK1.5.
  

When to go What?

• Is your operation is multithreaded ?: HashTable(less than jdk1.5).
• Is the datatype of key is Integer ? : HashTable has better performance if the data type of the key is Integer.
  

Difference between Arraylist Vs Vector

Arraylist Vs Vector

• Vector is synchronous but arraylist is asynchronous.

• Vector & Hashtables are introduced in JDK1.0 but Araaylist & HashMaps are introduced in JDK1.2.
• vector is comparatively slow with Arrraylist.
  

When to use what?

• If your data is accessed by multiple threads then go for Vector.
• If your list is a local variable then go for Arraylist blindly.
• If your data is accessed by a single thread then go for Arraylist.