java.util package explained completely.

In java java.util package is available. It is not default package in Java which means that you have to write import statement to use the features available in this pakcgae.

‘java.util’ package contains many utility classes, legacy classes and mainly collections framework.

The classes which have been introduced since the first version of Java are called as legacy classes.

The classes which are introduced from Java2 to manage the collection of elements/objects are collectively known as collection framework in Java.

Collection framework in Java is very important set of classes that lets you implement various data structures in java, effectively and easily.

To store the group of elements of same type you can use arrays but arrays have following limitations:

ü  You need to define the type of objects at the time declaration of array.

ü  You need to specify the size of array at the time declaration of array which can not be changed later.

ü  Insertion and deletion of elements in the middle positions of the array is not possible.

ü  You can not manage and access the elements of array effectively and easily.

To solve these problems and to handle the elements more effectively and easily following legacy classes are used in java:

            i.            Vector: Vector is a legacy class used to store objects or collections of elements without any key value or name value. You can collect all the objects in vector directly.

          ii.            Stack: Stack is also legacy class and it is used to stored objects, like vectors only.

        iii.            Hashtable: Can be used to store the objects or collections of objects as key and its corresponding name value.

        iv.            Dictionary: Can be used to store the objects or collections of objects as key and its corresponding name value.

          v.            Properties: Can be used to store the objects or collections of objects as key and its corresponding name value.

        vi.            Enumeration: Enumeration is interface defined in java.util package. The main purpose of using enumeration interface is to access the data stored in legacy classes one by one.

These legacy classes or collection framework has following advantages over arrays:

ü  You need not define the size of collection of objects, at the time of declaration. These legacy classes or collection framework uses the concept of capacity, which ensures the dynamic management of memory. Default capacity will be 10, if you are not defining the capacity initially.

ü  You need not to specify the data type of elements for which you are using the legacy classes or collections.

ü  You can access the elements of legacy classes or collections framework one by one so modification is easily possible.