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Tuesday, February 13, 2018

[Java8] Stream APIs

I recently moved to Java 8 and found some interesting feature added with Java 8.



Stream APIs
We will go through Stream apis added with Java collections. Stream api have sequential and parallel operation. We can apply these operation for filer/map/reduce/collect/flatmap. This is certainly helpful applying bulk operation on Collection. Besides parallel execution comes very handy with multi-core systems.

Lets see by an example. Create a dummy collection


  List<Integer> iList = new ArrayList<Integer>();
  for(int i=0; i<100; i++) iList.add(i);
Sequential Stream:


Stream<Integer> sequentialStream = iList.stream();
 sequentialStream.filter( i -> (i%2 == 0) ).forEach(System.out.println);
Parallel Stream:


Stream<Integer> parallelStream = myList.parallelStream();
 parallelStream.filter(i -> (i % 2 != 0 )).forEach(System.out.println);

[Java 8] what's new - Foreach

I recently moved to Java 8 and found some interesting feature added with Java 8.
I have listed few of them:


1. forEach method - Apply on all
First we will go through forEach method.
Create a dummy collection

  List<Integer> iList = new ArrayList<Integer>();
  for(int i=0; i<100; i++) iList.add(i);
Without Foreach

  Iterator<Integer> itr = iList.iterator();
  while(itr.hasNext()){
   System.out.println("Value:"+itr.next());
  }

With Foreach

  iList.forEach(new Consumer<Integer>() {
   public void accept(Integer i) {
    System.out.println("Value::"+i);
   }

  });
You might see not much change in term of line of code. What important thing to note here clear separation between business and iteration. You can easily write your code 
As we apply operation on collection, we are prone to ConcurrentModificationException if we wrongly operate on iterator. Foreach help with that operation. 

Tuesday, August 5, 2014

[Java] Creating Immutable Class

what is immutable class. A class whose object can not be modified.

So we have to make sure we have stop all the mechanism which allows user to change the stage.

* Member Variable - Make them final so no one can change state.
* Class as Final - So derived class can not override the behavior.
* No Setter method - So its can not be changed later in case you missed to  initialize in constructor.


public Final class DataReceiver
{
final string port_id;
public DataReceiver( String port)
this.port_id = port;
}

public String getPortID()
{
return port_number;
}
}

Above class will be used as immutable now. :)

[PUZZLE] Measure 50% water in Cylindrical glass

We have filled a cylindrical glass with water. We have to measure that  glass have exactly 50% of water. We don't have any measuring instrument. 

Solution:

Two ways can be there.

First tilt the glass to the point water reaches to brim of glass. This same point other side water should be exactly at upper bottom. If this happens them you have water half measured.
If water is lower than upper bottom then its less than 50% and if more than upper bottom then more than 50% water is there.

Other way is to mark the current level of water on glass by placing a finger there. 
Cover glass head with you palm or disc and turn over the glass. If water still touches marked location only then its exact half.

[PUZZLE] ELEPHANT AND BANANA PUZZLE

A merchant has bough some 3000 banana from market and want to bring them to his home which is 1000 km far from Market. He have a elephant which can carry maximum of 1000/- banana at time. That could have been easy but this elephant is very shrewd and he charges 1 banana for every one kilometer he travel.

Now we have to maximise number of banana which should reach to home.

Solution:

At present we are at 0th km with 3000 banana and elephant.
Lets see if elephant have to shift all the 3000 banana and elephant by 1 km.

For 1 km shift:

Take first 1000 banana and drop at 1st km. 2 banana consumed. One banana each for to and fro.
Second  1000 banana and drop at 1st km. 2 banana consumed.
Third 1000 banana and reach at 1st km. 1 banana consumed.

So all in all total 5 banana will be consumed if we shift a kilometer.

But that's not all, our total banana number are also reducing so we may have to reduce the number of turns too. And this will happen once we have reduced the banana by 1000 number. That means to reduce the count of banana by 1000 for first move we have to shift base to 200 km. See 5 banana for 1 km ratio i.e. 1000 banana / 5 = 200 km.

So we are now at 200th KMs with 2000 banana and elephant.

Post 200 km, for every 1 km shift in base;

Take first 1000 banana and drop at 1st km. 2 banana consumed. One banana each for to and fro.
Third 1000 banana and reach at 1st km. 1 banana consumed.

So all in all total 3 banana will be consumed if we shift a kilometer post 200 kms. 

Now the second phase will be to reduce the 1000 banana. So we can move to 1000/3 = 333.3 km maximum in this phase. 

So we will be moved to (200 + 333.3) 533.3  km base with 1000 banana.

Now onward we need only 1 banana for every km shift as elephant can carry all the 1000 banana and need not to come back. 
So out of 1000 banana, elephant will consume (1000 - 533.3) more banana to reach home.  

And total saved banana will be (1000 -(1000 -533.3)) = 533.3 banana.