CSci 133, Occasional Lecture Notes

Binary Search function from class, March 4, 2005

// Main, Fig. 11.2, p. 554
public static int
search (int[] a, int first, int size, int target)
{
int middle;

if (size <= 0)
    return -1;
else
{
    middle = first + size/2;
    if (target == a[middle])
      return middle;
    else if (target < a[middle])
      // the target is less than a[middle],
      // so search before the middle
      return search(a, first, size/2, target);
    else
      // the target must be greater than a[middle],
      // so search after the middle
      return search(a, middle+1, (size-1)/2, target);
}
}

Notes from Start of Semester on Classes, Methods, and Testing

Application Programs vs. Software Components (reusable classes)

The user of an application program is generally an end user, a person who's using the program to solve their problem, and whose main concern is that the program
- does what it's supposed to do, and
- behaves predictably no matter what the input.
The user of a reusable class is not an end user but another programmer.
We document application programs with user manuals; we document classes with a list of methods, including preconditions and postconditions for each method.
cs1.Keyboard and java.lang.Math are software components.

Writing Your Own ADT Classes

Sets of reusable classes are the basis for all modern software development, regardless of language or operating system.
An Abstract Data Type (ADT) class provides the necessary support for a data structure: the ability to instantiate objects of the class, and a set of methods to manipulate the objects.
An object has state (a set of data values, sometimes called fields or attributes) and behavior (a set of methods). The methods act on the data values, which changes the state.
The data values are usually private, so that a calling program can't access them directly but must call methods.
The methods are usually public, so a calling program can use them. Sometimes there are also private methods; why would we want these?

Characteristics of Data Values and Methods

Public methods and data values are visible and available to any program that imports the class; private methods and data values are "invisible" outside the class itself and can be directly referred to only within the class.
A static method or data value is associated with the class; a non-static one is associated with each object. That is, each object has its own "copy" of the method or data value.
A value-returning method is one that returns a value to the calling program; a void method is one that does not return a value. At this time we'll consider both value-returning and void methods.