Java collections

Differences between Arrays and Collections ?
Arrays Collections
1) Arrays are fixed in size. 1) Collections are growable in nature.
2) Memory point of view arrays are not recommended to use. 2) Memory point of view collections are highly recommended to use.
3) Performance point of view arrays are recommended to use. 3) Performance point of view collections are not recommended to use.
4) Arrays can hold only homogeneous data type elements. 4) Collections can hold both homogeneous and heterogeneous elements.
5) There is no underlying data structure for arrays and hence there is no readymade method support. 5) Every collection class is implemented based on some standard data structure and hence readymade method support is available.
6) Arrays can hold both primitives and object types. 6) Collections can hold only objects but not primitives.







Collection object:
An object is said to be collection object if it holds or stores a group of other objects.
Collection class:
A collection class is a class whose object can store group of other objects.
Ex:


Heap memory











The objects performed by s1,s2,s3 and s4 are stored multiple times there by wasting the memory with in the JVM.
To save the memory with in the jvm when the objects are stored in the collection object, the jvm stores the references of the objects with in the collection objects inside of storing the objects directly.

Heap memory












What is framework in java
o provides readymade architecture.
o represents set of classes and interface.
o is optional.


The collections are designed to store only objects that is the collections can not store primitive type values.
All the collection classes are available in “java.util” (utility) package.
All the collection interfaces and collection class and together as collection frame work.
All the collection classes are categorized into three groups’ i.e.