Friday, May 10, 2013
The heapsort algorithm starts by using BUILD-MAX-HEAP to build a max-heap on the input array A[1 : : n ],where n=A:length. Since the maximum element of the array is stored at the root A[1] , we can put it into its correct final osition by exchanging it with A[n] . If we now discard node n from the heap - and we can do so by simply decrementing A:heap-size-- we observe that the children of the root remain max-heaps, but the new root element might violate the max-heap property. All we need to do to restore the max-heap property, however, is call MAX-HEAPIFY(A, 1), which leaves a max-heap in A[1 : : n -1] . The heapsort algorithm then repeats this process for the max-heap of size n- 1 down to a heap of size 2.
     The program written below has build_max_heap() to build the max-heap, max_heapify() to retain the max-heap property and heap_sort() for sorting. The most important thing of the code is that you can use this to sort anything. Just pass an array of any object which is comparable i.e. implements Comparable interface or any array of wrapper class objects like Integer, Float etc. This is only beacause we have done this using Java's generics feature to make this code generic and general and no need for different implementations.
Heapsort operation
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Java Source Code
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import java.util.Scanner;

/*This code can take in any array of Comparable i.e whose data can be compared and generates the sorted elements using heap sort*/
public class HeapSort<E extends Comparable<? super E>>{
    private int heap_size;
private E A[];

public HeapSort(E a[]){
  A=a;
}

private void build_max_heap(){  //building max-heap
   heap_size=A.length-1;
   for(int i=heap_size/2;i>=0;i--)
  max_heapify(i);
}

private void swap(int i,int j){
   E tmp=A[i];
A[i]=A[j];
A[j]=tmp;
}

private void max_heapify(int i){
   int l=2*i,r=2*i+1;  //left and right child
int largest;
   if(l<=heap_size && A[l].compareTo(A[i])>0)
  largest=l;
else largest=i;
if(r<=heap_size && A[r].compareTo(A[largest])>0)
  largest=r;
if(largest!=i){    //finding largest, swapping and then reheapify
  swap(i,largest);
  max_heapify(largest);
}
}

public E[] heap_sort(){
   build_max_heap();
for(int i=A.length-1;i>=0;i--){
  swap(0,i);  //swapping with first
  heap_size--;  //decreasing size
  max_heapify(0);  //reheapify
}

return A;
}

public static void main(String[] args)throws Exception{
Scanner sc=new Scanner(System.in);
System.out.print("Enter size : ");
int n=sc.nextInt();
Integer a[]=new Integer[n];
System.out.println("Enter elements to be sorted -->");
for(int i=0;i<n;i++)
  a[i]=sc.nextInt();
  
HeapSort<Integer> obj=new HeapSort<Integer>(a);
a=obj.heap_sort();
System.out.println("Sorted array -->");
for(int i=0;i<n;i++)
  System.out.print(a[i]+"  ");
    }
}
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Saturday, May 4, 2013
Today I will tell you how you can get the parameter values submitted by a client to a server using servlets. Here you will see different process of extracting the form parameters depending on your requirements. Here we will use getParameter() , getParameterValues() , getParameterNames() and getParameterMap() methods.
 getParameter() : This method returns only a single value associated with the parameter name. This is generally used when you have only one value for a parameter.
getParameterValues() : It returns an array of all values associated with a parameter name. This is used when you have multiple values for a parameter.
getParameterNames() : It returns an Enumeration<String> which are the different parameter names. Now you can use individual name and extract the values. This is used when you dont know the param names. But in reality you will always know them from beforehand.
getParameterMap() : It returns a Map of parameter names mapped to all values associated with each parameter. This is the most general case.
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Servlet Source Code
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import java.util.Map;
import java.util.Set;
import java.util.Iterator;
import java.util.Enumeration;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.annotation.WebServlet;

@WebServlet("/paramReader")
public class ParamReader extends HttpServlet{
   public void doGet(HttpServletRequest req,HttpServletResponse res){
        //used when one parameter has only one value
String fn=req.getParameter("fn");

//used when one parameter has more than one vakue
String str[]=req.getParameterValues("fn");  //getting all values

//used when parameter names are unknown
Enumeration<String> en=req.getParameterNames();  //getting all names
while(en.hasMoreElements())
          req.getParameter(en.nextElement());  //getting vakue
     
      //used to get whole map
Map<String,String[]> m=req.getParameterMap();
Set<String> s=m.keySet();  //key set means param names
Iterator<String> it=s.iterator();
while(it.hasNext())
          m.get(it.next());  //param values
   }
}
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I am a student of BTech Computer Science Engineering from RCCIIT,Kolkata. I am a crazy lover of Java and wants to settle as a Java developer. I have a seven years Java experience with an application developer experience for 2 years. Recently from March 2012 I am a registered S40 app developer for Nokia and has corrected an app of them. I am currently writing blogs to encourage and grow interest in all those who don't know or learning Java.