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© The scientific sentence. 2010

Vectors
Vectors              The colored, to comment.

I. Introduction


Vector of objects is a class in Java. Instead of arrays, 
the class vector has many predefined methods that we can use. 
Its number of elements vary dynamically, depending on adding 
or retreiving elements from a vector. This class resides in 
java.util class. We have then to import it. Now, let's 
consider a vector of Circles. As we have alrady defined 
this class in TestCircles class, we import the class Circles 
in the same package and use it.We have the class Circles in the 
same package.

Here, we built  new Circles, by calling the constroctor 
of the class Circles,  as follows:

Circles Circle1 = new Circles (1.25) ,
	Circle2 = new Circles (2) ,
	Circle3 = new Circles (3.5) ,
	Circle4 = new Circles (4) ;
First, we put them in a vector as follows:
Vector TheCircles = new Vector(); by building a vector with 
the name TheCircles.
Next, we use the Java methods predefined in the class Vector:

TheCircles.addElment (Circle1);
TheCircles.addElment (Circle2); 

TheCircles.size(); return 2.

TheCircles.setElementAt (Circle3,2); will memorize 
Circle3 in the third index.

 Circles  Circlex = (Circles) TheCircles.elementAt(1); 
will return the Circle Circlex which is in the second position. 
 If we do not cast as (Circles), the statement 
will return an object from the Java class Object.
 
 TheCircles.insertElementAt (Circle4, 2); 
will insert the circle Circle4 in the third index of the vector.
 
 final boolean removeElement (Object theObject); 
remove the first element of the vector.
 
 final void removeElementAt(int Rank); 
remove the element at the index Rank.
 
 final void removeAllElements(); 
will empty the vector.
 
 final int indexOf (Object TheObject); 
Return the index of the first occurence of the oject TheObject.
 
  final int lastIndexOf (Object TheObject); 
Return the index of the last occurence of the oject TheObject.
  
  final boolean contains (Object TheObject); 
Return true if the object is present in the Vector; false if not.



II. The related code


import java.util.*; //import java.util.Vector;
public class Vectors{

static void Display(Vector TheVector, String Words){
System.out.println(Words);
if (TheVector.size() == 0)System.out.println("The 
vector is empty.");
else {
	System.out.println ("\n\t The vector has " + 
TheVector.size()+ " elements.");
	for (int i =0; i <TheVector.size(); i++)
	((Circles) TheVector.elementAt(i)).Display 
("\n\t at the index "  + i); // Display method of the class Cirles
	System.out.println();
	}

}



public static void main (String[] args){

// 1. Vector TheCircles = new Vector ();
// Construction of the vector TheCircles
Vector TheCircles = new Vector();
// Construction of the vector TheCircles
System.out.println("\n\t The number of elements 
in the vector TheCircles at first, is: " + TheCircles.size());

Circles Circle1 = new Circles (1.25) ,
		Circle2 = new Circles (2) ,
		Circle3 = new Circles (3.5) ,
		Circle4 = new Circles (4) ;
	
TheCircles.addElement(Circle1);
TheCircles.addElement(Circle2); 
TheCircles.addElement(Circle3);
TheCircles.addElement(Circle4); 
System.out.println("\n\t After adding 4 cercles, \n\t the 
number of elements in the vector TheCircles is: " + TheCircles.size());

Circles Circle5 = new Circles (10);

TheCircles.insertElementAt(Circle5,4);
System.out.println("\n\t After inserting an element, \n\t 
the number of elements in the vector TheCircles is: " + TheCircles.size());

//2. Circles  Circlex = (Circles) TheCircles.elementAt(3);
// casing
Circles  Circlex = TheCircles.elementAt(3);
System.out.println("\n\t The index of the elemnt Circle4 
\n\t in the vector is: " + TheCircles.indexOf(Circle4));
 
Circles Circle6 = new Circles (100);
TheCircles.setElementAt(Circle6,0);
System.out.println("\n\t After setting Cercle6, \n\t 
the number of elements in the vector TheCircles is: " + TheCircles.size());
 
 
TheCircles.removeElementAt(2);
System.out.println("\n\t After removing the third element, 
\n\t the number of elemnts in the vector TheCircles is: " + TheCircles.size());
System.out.println();


TheCircles.removeElementAt(0);
Display (TheCircles, "\n\t After removing the first element, 
we have:");// This Display


TheCircles.removeElementAt(0);
//3. ((Circles) TheCircles.firstElement()).Display (", first 
element of the vector");//casting
( TheCircles.firstElement()).Display (", first element of the vector");
// Display of the Circles class


System.out.println();
TheCircles.removeAllElements();
System.out.println("\n\t After removing all the elements, \n\t 
the number in the vector TheCircles is: " + TheCircles.size());

}

}//end of the class Vectors


III. Remarques

In the main method, the program runs ( no errors, and the 
class is built) with the lines commented 1.,2.,3., but 
it gives warinig regarding addElement and insertElement. 
which shown by the command : javac -Xlint  (with -Xlint option). 
To eliminate the wornings add the brackets after Vector; that 
is Vector (here the vector uses the class Circles), 
and eliminate the casting.




IV. Execution


C:\Java>java Vectors

         The number of elements in the vector TheCircles at first, is: 0

         After adding 4 cercles,
         the number of elements in the vector TheCircles is: 4

         After inserting an element,
         the number of elements in the vector TheCircles is: 5

         The index of the elemnt Circle4
         in the vector is: 3

         After setting Cercle6,
         the number of elements in the vector TheCircles is: 5

         After removing the third element,
         the number of elemnts in the vector TheCircles is: 4


         After removing the first element, we have:

         The vector has 3 elements.

         The circle
         at the index 0 has the
         Surface = 12.566370614359172

         The circle
         at the index 1 has the
         Surface = 50.26548245743669

         The circle
         at the index 2 has the
         Surface = 314.1592653589793


         The circle, first element of the vector has the
         Surface = 50.26548245743669


         After removing all the elements,
         the number in the vector TheCircles is: 0

C:\Java>



  
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