Vectors

[chili5]

Vectors in Java

A Vector is a container that expands in size as new data is added. The Vector container cannot hold primitive variables. In can only hold objects. Therefore, if you wish to include a primitive data type in a vector you must use it's wrapper class.

Table 1.1 Primitive Wrapper Classes



By using the new operator with any of the wrapper classes, you can add a primitive variable to the vector.

For example:

Integer nPrime = new Integer(5);
Boolean bPrime = new Boolean(false);

Making a Vector

You must first import the java.util.Vector class.


Constructors

The Vector class contains four constructors:

Vector();
Vector(Collection coData);
Vector(int nSize);
Vector(int nSize, int nCapacity);

If you use the first constructor, an empty vector is created with a default size of 10, and it's capacity increment is zero.
The second Vector constructor takes a Collection and populates the vector with the elements in the collection.
The third Vector constructor takes a single integer that specifies the beginning size of the constructor.
The forth constructor takes a integer specifiy the beginning size of the constructor and a second integer that specifies the increment.

Adding to a Vector

First create a Vector object. We will populate this vector with information about 3 people. This will include the following data:

1. Name (String)
2. Age (Integer)
3. Gender (Boolean - true represents male and false represents female)
4. Middle Initial (Character)


The data we want to add to the vector is this:

Table 1.2 Example data


Since we can only have objects added to our vector, we need to create a String object, an Integer object, a Boolean object, and a Character object. I am going to pass the four objects to a method that illustrates how to return a Vector.

public class VectorTest {

    public static void main(String[] args) {
        Vector vPerson = new Vector(); // a vector that has a size of 10

        String sName;
        Integer nAge;
        Boolean bGender;
        Character cInitial;
        
        sName = "James"; // notice that there isn't a new String("James") line here. This isn't required, as Java has created a short form for assigning Strings. However I could have done sName = new String("James");
        nAge = new Integer(16);
        bGender = new Boolean(true);
        cInitial = new Character('G');
        
        vPerson = addElements(vPerson, sName, nAge, bGender, cInitial);
        
        
        sName = "Harry";
        nAge = new Integer(25000);
        bGender = new Boolean(false);
        cInitial = new Character('R');
        
        vPerson = addElements(vPerson, sName, nAge, bGender, cInitial);
        
        sName = "Flipper";
        nAge = new Integer(97400);
        bGender = new Boolean(true);
        cInitial = new Character('A');
        
        vPerson = addElements(vPerson, sName, nAge, bGender, cInitial);
    }
    
    public static Vector addElements(Vector vPerson, String sName, Integer nAge, Boolean bGender, Character cInitial) {
        vPerson.add(sName);
        vPerson.add(nAge);
        vPerson.add(bGender);
        vPerson.add(cInitial);
        
        return vPerson;
    }
    
}

The .add() method of the vector adds the specified element to the next space available in the Vector. I pass to a method the Vector, and the four elements that I wish to add to the Vector. The method adds the four elements to the vector, and returns the modified Vector.

Now to output the results, I create a List iterator and four temporary primitive variables to hold the results.

Like so:

ListIterator iterator = vPerson.listIterator();
String sTempName;
int nTempAge;
boolean bTempGender;
char cTempInitial;

 while (iterator.hasNext()) {
            sTempName = iterator.next().toString();
            nTempAge = Integer.parseInt(iterator.next().toString());
            bTempGender = (Boolean)iterator.next();
            cTempInitial = (iterator.next().toString().charAt(0));
            System.out.print(sTempName + " " + cTempInitial + " is " + nTempAge + " years old,");
            if (bTempGender) {
                System.out.print(" and is a male.");
            } else {
                System.out.print(" and is a female.");
            }
            System.out.println();
        }

The iterator returns an Object, which I then convert to a String and using the wrapper class converting into back into the primitive data type.

This code produces this output:

James G is 16 years old, and is a male.
Harry R is 25000 years old, and is a female.
Flipper A is 97400 years old, and is a male.

I've just covered adding elements to the Vector but you can remove elements from the Vector.

Please note, that this is just an example. In an ideal situation, you would create a Person class. In which you could add Person objects to the Vector.

Hope this was helpful!

Enjoy,
James

External resources:

Java: Vectors
Vector (Java 2 Platform SE v1.4.2)

[Jordan]

Very nice tutorial, chili5! +rep

[Turk4n]

Very interesting !

[WingedPanther]

Nice. I've always found Java's insistence on wrapper classes to access primitives annoying, though.

[Xav]

James CC

Did you change your surname?

[chili5]

lol that was a typo.

@winged - Do you know why sun decided we have to use wrappers and not primitives? I find wrappers annoying also.

[Xav]

Sure it was.

[WingedPanther]

Java views classes as being a different type of data than primitives. This is different from C++'s perspective that classes and primitives should be equivalent. I think it's about Java's desire to be pure OOP, but still having to support primitives.

[mendim.]

Nice Tutorial , +rep .!

[Egz0N]

Nice Job .. +rep