Class 32: Vectors (2)

Held: Wednesday, 26 October 2005

Summary: Today we revisit key issues of Vectors and check your understanding of the API.

Related Pages:

• EBoard.
• Sample vector code.
• API for java.util.Vector.

Notes:

• Assignment: Find (or replicate) our two recursive versions of exponentiation and extend the two to count the number of steps a call takes.
• Today's class will end at 11:30.
• Professor Walker will be observing class on Friday, Monday, and Tuesday.

Overview:

• Vectors, concluded.

Vectors, Revisited

• As many of you noted, vectors have both a size and a capacity.
  • The size reflects how many valid positions there are in the vector
  • That is, the valid indices are 0 to v.size()-1.
  • The capacity reflects the length of the underlying array.

• Remember that vectors are parameterized. Hence, when you declare vector variables and construct vectors, you need to include the type of the elements.
• That is, use

  Vector<String> stuff = new Vector<String>();
  

  rather than

  Vector stuff = new Vector();
  

• Java 1.5 includes a new control structure appropriate for vectors and other collections. This structure is called the "for each" or "extended for". It permits you to iterate through the values in the collection.
• The form is

  for (type name : collection) 
  {
    stuff-to-do
  }
  

• This code evaluates stuff-to-do once for each value in the collection, setting name to the current value before executing stuff-do-do.

• Vectors include many too many operations for adding values, including
  • add(E element)
  • add(int index, E element)
  • insertElementAt(E element, int index)
  • set(int index, E element)
  • setElementAt(E element, int index)
• What is the difference between these operations?
• Why do you think that the designers included so many similar operations?