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Methods
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Divide and conquer
Programmer-declared methods
Prepackaged methods – Java API
Software reusability
Debug-ability and maintainability
AKA functions or procedures
Java API
Application Programming Interface
java.sun.com/j2se/1.4.1/docs/api/index.html
• Reduces programming development time
• Avoids introducing programming errors
• Examples:
– Math class methods
– String class methods
– Integer class methods
Example:
Programmer defined method
Uses prepackaged Math class method
Import java.awt.Container;
Import javax.swing;
Public class PowerTest extends JApplet{
public void init ()
{
String s1 = JOptionPane.showInputDialog(“Enter the base value”);
String s2 = JOptionPane.showInputDialog(“Enter the exponent value”);
double base = Double.parseDouble (s1);
double exponent = Double.parseDouble (s2);
double power = computePower (base, exponent);
JTextArea outputArea = new JTextArea();
outputArea.setText (base + “ raised to the power of : “ + exponent + “ = “ + power);
Container container = getContentPane ();
container.add (outputArea);
}
public double computePower (double x, double y)
{
return Math.pow(x,y);
}//end computePower
}//end PowerTest
Recursion!
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P. 250 - 259
Calls itself directly or indirectly
Has a base case which ends recursion
Recursive calls result in simpler problems
which get closer to the base case
Each recursive call is added to the stack
Memory can become exhausted
Example of simple recursion:
Fibonacci sequence p. 253-258
0,1,1,2,3,5,8,13,21,…
public long fibonacci (long n)
{
// base case
if (n == 0 || n == 1)
return n;
//recursive call
else
return fibonacci (n–1) + fibonacci (n–2);
} //end fibonacci
Arrays!
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Data structure
Object
A list of elements of the same type
Elements referenced: subscript or index
Index starts with zero
Length field
For loops
Bubble Sort
p. 298
public void bubbleSort (int array[ ])
{
for (int pass = 1; pass < array.length; pass++) {
for (int element = 0; element < array.length -1; element++)
{
if (array [element] > array [element +1] )
swap (array, element, element + 1);
}//end inner for loop for comparisons
}//end outer for loop to control passes
}//end bubbleSort
Binary Search
p. 302-306
public int binarySearch (int array[ ], int key)
{
int low = 0;
int high = array.length – 1;
int middle;
while (low <= high)
{
middle = (low + high) / 2;
buildOuput (array, low, middle, high);
if (key == array [middle] )
return middle;
else if (key < array [middle] )
high = middle – 1;
else
low = middle + 1;
}//end while
return -1;
}//end binarySearch
Multidimensional Array Example
p. 312-313 – building output string for a twodimensional array
public void buildString ( )
{
output += “
“;
for (int counter = 0; counter < exams; counter++ )
output += “[“ + counter + “] “;
for (int row = 0; row < students; row++)
{
output += “\ngrades [“ + row + “] “;
for (int column = 0; column < exams; column++)
output += grades [row] [column] + “ “;
}//end outer for
}//end buildString
Summary
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Read over the chapters and these slides
Ask questions!
Practice!
Next step:
– Get in your teams
– Get your assignment
– See what you can do
“Review” Programming Assignment
Write an applet that prints a table that tells us the fate of
our $10,000 investment under various interest rate
scenarios (from 5% to 10% in increments of 0.50%) if we
keep the money for 5, 10, 15, 20, and 30 years. Note,
that if we keep the money for 30 years, that investment
grows to almost $200,000 at 10% interest!
Your solution should involve applets, methods, arrays,
repetition, and selection. All of our review topics!
Get started now in lab by working together to design your
test code and writing your psued-ocode (CALTAL). Work
with another person to brainstorm about a plan. Turn in
what you come up with at the end of today’s lab.
Now, on your own, finish! Due one week from today.