• A vector is an ordered sequence of objects.
• It can be of any length.
• Objects can be inserted anywhere in the sequence or appended to the end.
• Objects in the sequence can be replaced or modified.
• Objects in the can be of any type (they don't have to all be the same type).

• Java defines a Vector class in the package java.util.
• To use Vector in a source file, you must include at the top of a file:

  import java.util.*;
  

• Vector elements are labeled starting at 0.

• Vector() - construct an empty vector.
• size() - return the number of objects in the vector.
• elementAt(i) - return the object at place i in the vector.
• addElement(obj) - append the object obj to the end of the vector.
• setElementAt(obj, i) - replace the object at position i with obj.
• insertElementAt(obj, i) - insert object obj at position i and move everything over.
• removeElementAt(i) - remove the object at position i and shift everything over.

Vector apanel = new Vector(); 

Button abutton;
abutton = new Button("Water");
apanel.addElement(abutton);
abutton = new Button("Soda"):
apanel.addElement(abutton);

for (int i = 0; i < apanel.size(); i++) {
    Button b = (Button)apanel.elementAt(i); //get reference to the button
    b.PushButton();
}

• The elements in a vector are objects. If you want an element to be a primitive type (e.g. int) you have to use a wrapper class.
• The wrapper classes for primitive types are: Integer, Boolean, Character, and Double.
• When you use an element of a Vector for something, in general you have to type cast it.
• An exception to the type casting rule is printing with System.out.println because that method calls the object's toString.

public class ClassList {
   private Vector myNames;
   private int myCurrentEnrollment;
   private String myCourseTitle;

   public ClassList(String title) { 
      myName = new Vector();
      myCurrentEnrollment = 0;
      myCourseTitle = new String(title);
   }

   // accessors
   public int getEnrollment() {
      return myCurrentEnrollment;
   }

   public String getTitle() {
      return myCourseTitle;
   }
          
   public void printClassList() {
      System.out.println("\n The class list for " + myCourseTitle);
      for (int i = 0; i < myNames.size(); i++)
          System.out.println((String)myNames.elementAt(i));
   }

   // Modifiers
   public boolean addStudent (String name) {
      if (searchStudent(name) != -1)
         return false;
      int pos = findInsertionPosition(name);
      myNames.addElementAt(name, pos);
      myCurrentEnrollment++;
      return true;
   }

   public boolean dropStudent (String name) {
      int pos = searchStudent(name);
      if (pos == -1)
         return false;
      myNames.removeElementAt(pos);
      myCurrentEnrollment--;
      return true;
   }
         
   //private helpers
   private int searchStudent (String name) {
      int high = myNames.size();
      int low = 0;
      while (low <= high) {
         int mid = (low + high)/2;
         String temp = (String)myNames.elementAt(mid);
         if (temp.equals(name))
            return mid;
         else if (temp.compareTo(name) < 0)
            low = mid + 1;
         else
            high = mid - 1;
      }
      return -1;
   } 
         
   private int findInsertionPosition(String name) {
      if (myNames.size() == 0)  // class list is empty 
         return 0;
      for (int i = 0; i < myNames.size(); i++) {
          String temp = (String)myNames.elementAt(i); 
          if (temp.compareTo(name) > 0)
             return i;
      }
      return myNames.size();  // insert at the end 
   }
}