私は NetBeans を使用して、書籍を検索するための参照番号を使用して一種のライブラリ データベースをプログラミングしています。線形検索と二分検索の両方を使用して、参照番号がライブラリにあるかどうかを判断していますが、二分検索は真であるべきときに偽を返し続けます。これは私の全体的なコードがどのように見えるかです:
package u3a3_bookslist;
import java.util.*;
import java.io.*;
public class bookslist {
//Define the default variables to use in all other methods of the program
public static int index, numSearches;
public static void main(String[] args) {
//Define the ArrayList to store the values of 'BookList.txt'
ArrayList <String> books = new ArrayList <String>();
//Define the default values to use later in the code
BufferedReader br = null;
String referenceNumber;
//Use a try statement to analyze the entire 'BookList.txt' file and add
//each value on a new line into the arrayList 'books'
try {
br = new BufferedReader(new FileReader("BookList.txt"));
String word;
while ((word = br.readLine()) != null ){
books.add(word);
}
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
br.close();
} catch (IOException ex) {
ex.printStackTrace();
}
}
//Create a new Array called 'bookList' to store and convert all the values
//from the 'books' arrayList
String [] bookList = new String[books.size()];
books.toArray(bookList);
//Create a scanner input to ask the user to enter a reference number
Scanner input = new Scanner(System.in);
System.out.println("Enter the reference number of a book to determine"
+ " if it is in the library or not: ");
//Set the variable 'referenceNumber' to whatever value that the user inputted
//into the Scanner
referenceNumber = input.next();
//Obtain the boolean result of either true or false from the Binary and
//Linear search methods
Boolean resultLinear = linearSearch(bookList, referenceNumber);
Boolean resultBinary = binarySearch(bookList, 0, bookList.length-1, referenceNumber);
//Analyze each element that is contained in the 'bookList' Array
for (int i = 0; i < bookList.length; i++) {
//Determine if the value of 'i' is equal to the 'referenceNumber'
//converted into an int format
if (i == Integer.parseInt(referenceNumber)) {
//Determine if the 'i' index of the 'bookList' Array is equal
//to the user inputted reference number
if (bookList[i].equals(referenceNumber)) {
//If the previous statement were true, the 'index' variable
//was set to equal to current value for 'i'
index = i;
}
}
}
//Determine the message to display to the user depending on if the reference
//number was found in the Array using a Linear Search
if (resultLinear == true) {
System.out.println("Linear Search: Reference Number " + referenceNumber +
" was found in the library. The book with that number is: " + bookList[index+1]);
} else {
System.out.println("Linear Search: Reference Number " + referenceNumber
+ " not in the library. No book with that number.");
}
//Determine the message to display to the user depending on if the reference
//number was found in the Array using a Binary search
if (resultBinary != false) {
System.out.println("Binary Search: Reference Number " + referenceNumber +
" was found in the library. The book with that number is: " + bookList[index+1]);
} else {
System.out.println("Binary Search: Reference Number " + referenceNumber
+ " not in the library. No book with that number.");
}
}
//Execute a linear search to determine if the user inputted reference number
//is contained in the bookList Array
static public Boolean linearSearch(String[] A, String B) {
for (int k = 0; k < A.length; k++) {
if (A[k].equals(B)) {
return true;
}
}
return false;
}
//Execute a binary search to determine if the user inputted reference number
//is contained in the bookList Array
public static Boolean binarySearch(String[] A, int left, int right, String V) {
int middle;
numSearches ++;
if (left > right) {
return false;
}
middle = (left + right)/2;
int compare = V.compareTo(A[middle]);
if (compare == 0) {
return true;
}
if (compare < 0) {
return binarySearch(A, left, middle-1, V);
} else {
return binarySearch(A, middle + 1, right, V);
}
}
}
私が問題を抱えているプログラムの部分はこの部分です：
public static Boolean binarySearch(String[] A, int left, int right, String V) {
int middle;
numSearches ++;
if (left > right) {
return false;
}
middle = (left + right)/2;
int compare = V.compareTo(A[middle]);
if (compare == 0) {
return true;
}
if (compare < 0) {
return binarySearch(A, left, middle-1, V);
} else {
return binarySearch(A, middle + 1, right, V);
}
}
True であるはずのバイナリ検索がなぜ false を返すのか、私には理解できません。線形検索でも、true の場合は true を返します。