در مورد Java.IO

1. 1. The data transfer occurs in the format of streams in java. we can transfer the data in and out.
   2. The constructor of System class is defined as private; we can not create object of system class. In System class there are 3 static variables 1-in 2-out 3-error   
   • in: is the object of InputStream class.
   • out: is the object of PrintStream class.
   • err: is the object of PrintStream class.

چند نکته در مورد Collection- map در جاوا

1. map stores the data  (key, value) pair
2. map does not support duplicate key
3. key can not but value can be duplicate
4. map hs two implemented clases 1-hash map 2-hash table
   
   • hash map: this store the element in (key, value) pair and allows null values
   • hash map is not synchronized by default
   • Hash table: this doesn't allow any null value and it is synchronized by default

چند نکته در مورد Stack در جاوا

1. Stack is another class of list interface that does all the operations on the top of the collection.
2. stack supports LIFO operation. last in first operation.
3. stack support some methods to do this operations. those are:
   1-push: adds the element to the top of the stack.
   2-pop: deletes the the top most element from the stack.
   3-peek: returns data most elevate from the stack.

List در جاوا

• List is another interface present in java API for collection.
• list has of 4 different implemented classes {Array list, link list; stack and vector}
• list supports the duplicate values and stores the data in the same manner how we had provided.
• Array list support all feature of list. but store the data in Array format.
• Array list is not synchronized by nature.
• Array list w1 = new Array list (10) Array list increases the size by 50 % of it's initial size.
• Array list is not synchronized but vector is synchronized.
• vector is same as array list. but it is not synchronized by default. the size of the vector increases by double the initial size.
  

Itrator Interface در جاوا

• • Itrator is an interface that retrieve the data one after an other.
  • Itrator supports some methods.
  • hs.next() this method return true if the next element is present in the collection else return false.
  • next() method return the next element from the collection.
  • we have to create the object of itrator interface using the method Itrator. example: Itrator ir = ar.itrator();