Chapter 3 Vector Class

Agenda Design and Implementation of Vector class – add, get, set remove, copy, equals, ensureCapacity Hangman using Vector class Word Frequency L-system Installing bailey.jar in BlueJ and Eclipse

Bailey’s Vector Interface (similar to java.util.Vector)

Rest of interface

Creating a list

Adding values to a list

Removing an item

Adding at a given location

Demo Programs

Implementation

Algorithm Development size() is easy (return elementCount;) What about delete(2) ?? – Before, list= ABCCDEFGHIJKL – After, list= ABCDEFGHIJKL – Some kind of shifting required for loop – If we try to guess it, we’ll most likely fail – Is there a method to developing a correct alg.? 11

Algorithm Method 1.Start with a specific function call – With specific data & arguments, i.e. set up list with ABCDEFG list.remove(3); 2. Draw a picture of data structure – Before and after function is called – Required for any assistance from instructor!! 3.Write out statements without any loop 4.Generalize into loop that works for all args 5.Add assert to prevent bad calls 12

Before and after remove(3)

Non-looping Specific Solution For our particular case, index (letter to erase) is 3 Statements to solve our example case: elementData[3] = elementData[4]; elementData[4] = elementData[5]; elementData[5] = elementData[6];  why is this the last copy? Then elementData[6] = null; // free the memory elementCount--; // we are now one shorter 14

Formulate the General Soln We can now see that – 3 in the first statement is really index. – 6 in the last statement is size of the list - 1 Therefore we can derive: public void delete(int index) { for (int k=index; k < elementCount-1; k++) elementData[k] = elementData[k+1]; elementData[elementCount-1]=null; elementCount--; } And check desired statements are produced by for loop 15

Importing bailey.jar Eclipse: Copy bailey.jar into your workspace folder Then, To configure build classpath, in Eclipse Project Properties Window, click Java Build Path in the left panel, and in the right panel choose Libraries tab. There are more classpath-related elements in Eclipse: JARs, External JARS, Variables, Libraries, Class Folders, and other Projects. Click Add External JARs (not Add JARS) if you want to add a jar file to classpath, and click Add Class Folders if you want to add a directory or folder to classpath. BlueJ: copy bailey.jar into the C:/BlueJ/lib/userlib folder

Inheritance from Eck Access modifiers such as public and private are used to control access to members of a class. There is one more access modifier, protected, that comes into the picture when subclasses are taken into consideration. When protected is applied as an access modifier to a method or member variable in a class, that member can be used in subclasses -- direct or indirect -- of the class in which it is defined, but it cannot be used in non-subclasses. (There is one exception: A protected member can also be accessed by any class in the same package as the class that contains the protected member. Recall that using no access modifier makes a member accessible to classes in the same package, and nowhere else. Using the protected modifier is strictly more liberal than using no modifier at all: It allows access from classes in the same package and from subclasses that are not in the same package.)

Super() from Eck Obviously, there has to be some fix for this, and there is. It involves the special variable, super. As the very first statement in a constructor, you can use super to call a constructor from the superclass. The notation for this is a bit ugly and misleading, and it can only be used in this one particular circumstance: It looks like you are calling super as a subroutine (even though super is not a subroutine and you can't call constructors the same way you call other subroutines anyway). As an example, assume that the PairOfDice class has a constructor that takes two integers as parameters. Consider a subclass: public class GraphicalDice extends PairOfDice { public GraphicalDice() { // Constructor for this class. super(3,4); // Call the constructor from the // PairOfDice class, with parameters 3, 4. initializeGraphics(); // Do some initialization specific // to the GraphicalDice class. }.. // More constructors, methods, variables.... } The statement "super(3,4);" calls the constructor from the superclass. This call must be the first line of the constructor in the subclass. Note that if you don't explicitly call a constructor from the superclass in this way, then the default constructor from the superclass, the one with no parameters, will be called automatically.