What is difference between HashMap and Hashtable classs


  1. Synchronization & Thread Safe - All methods in Hashtable are synchronized and thread safe whereas methods in HashMap are not synchronized and it is not thread safe.
    HashMap is more faster than Hashtable because its methods are not synchronized.
  2. Null Key & Null Value - HashMap allows one null key and any number of null values whereas null key and null value is not allowed in Hashtable. Hashtable's put method will throw NullPointerException if null is used as key or value
  3. Iterating the values - HashMap uses Iterator to iterate over the values whereas Hashtable uses Enumerator.
  4. Super class & Lagacy - Hashtable is subclass of Dictionary class which is now obsolete in JDK1.7. HashMap is sub class of AbstractMap
    Note :- It is better of externally synchronize a HashMap or Using concurrentMap implementation. (i.e. ConcurrentHashMap)

Comments

Post a Comment

Popular posts from this blog

Data types and Literals in Java

Image
Data types Data types category:   Data types summary: Literals A constant value which can be assigned to variable is called "Literal". Integral Literals All possible value of Integral data type(byte, short, int and long) are called Integral Literals. Default Value: By default every Integral literal is int type. When you assign a value in long data byte and that value is more than 2147483647(Maximum value for int) then compiler will give you error. Ex: long a = 3000000000; Error: The literal 3000000000 of type int is out of range  Even though we have used long data type and value is also within range of long but still compiler gives error because every integral literal is int type. We can resolve this error by specifying long type explicitly. We can specify long type by suffixing l or L . Ex: long a = 3000000000L; Number System: Integral Literal can be represented as Decimal, Octal and Hexadecimal number systems. Let's
Read more

How to define Auxiliary Constructor in case class in Scala

We have seen case class previously. We had discussed what is case class, how to create object of case class, list of boilerplate code generated for case class. If you don't know case class, I recommend to understand case class first. Let us revise case class declaration. case class Person(id:Int, name: String) Person class is declared with primary constructor where id and name are parameter. So good so far. The constructor which is not primary constructor, other than primary constructors and overloaded to primary constructor are called auxiliary constructor. How will you declare Auxiliary(other overloaded) constructors. What is syntax of creating auxiliary constructor. Please note that constructors in case class are not really constructor. Actually these are apply methods on companion object. Auxiliary constructor in case class are different than regular class. We can add auxiliary constructors in case class by adding apply() methods in companion object of case class
Read more

equals() method of Object class in Java

Image
When you compare two object references using == operator, it evaluate to true only when both references refer to same object. public class Person { private Integer id; private String name; public Person(Integer id, String name) { this.id = id; this.name = name; } public static void main(String[] args) { Person p1 = new Person(1, "Prithvi"); Person p2 = p1; Person p3= new Person(1, "Prithvi"); System.out.println(p1==p2); System.out.println(p1==p3); } } Output: true false We have created 3 references of Person class. Object references p1 and p2 both refer to same object so comparison evaluate to true. Comparison of p1 and p3 evaluate to false, even though p3 has same contents as p1 but refer to different object so comparison returns false. Below image explains this - Objects p3 and p1 are meaningfully equal. We must have some way to see their content are same or not. But the question is, How will you compare two different object
Read more