Class 42: Vectors

Held: Monday, 15 November 2004

Summary: Today we consider the standard Java class java.util.Vector. Vectors are the kitchen sinks of data structures: Vectors are much like expandable arrays, but they also provide a wide variety of other methods.

Related Pages:

• EBoard.
• Vector API.
• VectorTest.java.
• ExtendedVector.java.

Overview:

• Vector philosophy
• Vector methods
• Detour: Static methods
• Detour: Improving testing
• Vector applications

The Core Ideas of java.util.Vector

• java.util.Vector is one of the most useful (and generally used) utility classes in Java.
• From one perspective, Vectors are just expandable arrays.
  • You should know how to implement such things.
• Vectors make an interesting decision: You must explicitly set the size or add things at the end.
  • You can't just set something beyond the current end of the vector.
• Vectors also implement a host of other methods. (I call them the kitchen sink of data structures as a play on the phrase everything but the kitchen sink.)
  • Most involve things you'd like to do when using arrays to implement other data structures (inserting or removing something and having everything else shift, etc.)

Important Methods

• We'll test each method as we go.
• get, set, and setSize
• Variants of add
• remove
• Iterators
• Others

Testing

• Much of our testing involves reading output.
• How can we simplify the generation of that output? (E.g., when we repeat code?)
  • Write another method.
  • But that method is associated with the class, rather than individual objects
  • Hence, use static (for "class method")
• Rather than reading the output, we might check it automatically and only print a note when an error occurs.
• See the example for more details.