Problem with Binary search method

[lenois]

here is the whole program

import java.io.*;
import javax.swing.JOptionPane;

public class SortingSearching
{
	public static void main (String[]args)throws IOException
	{
		String[]fileNames=new String [2];
		String[]inputData= new String[20];
		String[]sortedList;
		int ct;
		
		fileNames=getFileNames(fileNames);
		ct=readFile(fileNames,inputData);
		System.out.println(ct);
		sortedList=sortFile(inputData,ct);
		printToFile(sortedList,fileNames,ct);
		searchList(sortedList,ct);
				
				
		
	}
	/************************************************************************
	*Function getFileNames ||this function gets user inputed filenames and	*
	*stores them in a string array for later use.									*
	*Pre:fileNames array Post:returns the array with the filenames				*
	*************************************************************************/
	public static String[] getFileNames(String[]fileNames)
	{
		fileNames[0]=JOptionPane.showInputDialog("Please enter name of input File:");
		fileNames[1]=JOptionPane.showInputDialog("Please enter name of output File:");
		
		return fileNames;
	}
	/***************************************************************************
	*Function readFile ||This function reads the text in the user chosen		 	*
	*file and stores up to 20 in a string array.											*
	*Pre:fileNames, inputData arrays Post:returns up to 20 strings in inputData*
	****************************************************************************/
	public static int readFile(String[]fileNames,
											  String[]inputData)throws IOException
	{
		int i=0;
		boolean test=false;
		String holder;
		
		BufferedReader inFile = 
                     new BufferedReader( new FileReader(fileNames[0]+".txt"));
		
		while(test!=true)
		{
			holder=inFile.readLine();
			if (holder==null)
			{
				test=true;
			}else if(i==20)
			{
			 	test=true;
			}else
			{
				inputData[i]=holder;
				i++;
			}
			
		}
		inFile.close();	
		
		return i;
	}
	
	/************************************************************************
	*Function sortFile ||this function sorts the data aquired by readFile	*
	*and uses an improved bubble sort to sort them									*
	*Pre:inputData Array Post:returns a sorted array with the filenames				*
	*************************************************************************/
	public static String[] sortFile(String[] inputData,
											  int ct)
	{
		int lastPos;
		int index;
		String temp;
		
		
		for(lastPos=ct; lastPos>=0; lastPos--)
		{
			for(index=0;index<ct;index++)
			{
				if(inputData[index+1]!=null&&index<ct)
				{					
					if(inputData[index].compareTo(inputData[index+1])>0)
					{
						temp=inputData[index];
						inputData[index]=inputData[index+1];
						inputData[index+1]=temp;
					
					}
				}
			}
		}
	return inputData;
	}
	/************************************************************************
	*Function printToFile ||this function prints the sorted array to a file	*
	*																								*
	*Pre:SortedList array Post:none														*
	*************************************************************************/
	public static void printToFile(String[] sortedList,
											 String[] fileNames,
											 int ct)throws IOException
	{
		PrintWriter outFile=
						new PrintWriter(fileNames[1]+".txt");
		int index=0;
		
		for(index=0;index<ct;index++)
		{
			
			outFile.println(index+"  "+sortedList[index]);//prints the sorted array to a file
			
		}
		outFile.close();
	}
	/************************************************************************
	*Function searchList ||function Searches list for user inputted word		*
	*																								*
	*Pre:SortedList array Post:none														*
	*************************************************************************/
	public static void searchList(String[] sortedList,
											int ct)
	{
		String input;
		input=JOptionPane.showInputDialog("Please enter a word to search for, or stop to stop");
		
		
		
		while(!input.equalsIgnoreCase("stop"))
		{
			
			int first=0;
			int last=ct-1;
			int position=-1;
			boolean found=false;
			int middle;
			
			
			System.out.println(last);
			
			
			middle=(first=last)/2;
			
			while(!found&&first<last)
			{       middle=(first+last)/2;
				if(sortedList[middle].equalsIgnoreCase(input))
				{
					found=true;
					position=middle; 
				}else if(sortedList[middle].compareTo(input)>0)
				{
					first=middle+1;
				}else
				{
					last=middle-1;
				}
			}
			JOptionPane.showMessageDialog(null,input+" found at position "+position); 
			input=JOptionPane.showInputDialog("Please enter a word to search for, or stop to stop");	
		}
	}
}

The last Method is the one that is not working. It is a simple binary search, but no matter whether the input is there or not, it returns -1. No errors are reported.

[lenois]

Never mind I fixed it, i had a simple typo.

but any comment on the code itself would be useful. Whether it is readable, are there too many loops, and other ways to improve it.

[Ronin]

Hi lenois,

if(inputData[index+1]!=null&&index<ct)

The above comment is enclosed in a for loop which already checks if index is smaller than ct. The last part of the above code on line 88 is redundant.

Regards.

[lenois]

import java.io.*;
import javax.swing.JOptionPane;

public class SortingSearching
{
	public static void main (String[]args)throws IOException
	{
		String[]fileNames=new String [2];
		String[]inputData= new String[20];
		String[]sortedList;
		int ct;
		
		fileNames=getFileNames(fileNames);
		ct=readFile(fileNames,inputData);
		sortedList=sortFile(inputData,ct);
		printToFile(sortedList,fileNames,ct);
		searchList(sortedList,ct);
				
				
		
	}
	/************************************************************************
	*Function getFileNames ||this function gets user inputed filenames and	*
	*stores them in a string array for later use.									*
	*Pre:fileNames array Post:returns the array with the filenames				*
	*************************************************************************/
	public static String[] getFileNames(String[]fileNames)
	{
		fileNames[0]=JOptionPane.showInputDialog("Please enter name of input File:");
		fileNames[1]=JOptionPane.showInputDialog("Please enter name of output File:");
		
		return fileNames;
	}
	/***************************************************************************
	*Function readFile ||This function reads the text in the user chosen		 	*
	*file and stores up to 20 in a string array.											*
	*Pre:fileNames, inputData arrays Post:returns up to 20 strings in inputData*
	****************************************************************************/
	public static int readFile(String[]fileNames,
											  String[]inputData)throws IOException
	{
		int i=0;
		boolean test=false;
		String holder;
		
		BufferedReader inFile = 
                     new BufferedReader( new FileReader(fileNames[0]+".txt"));
		
		while(test!=true)
		{
			holder=inFile.readLine();
			if (holder==null)
			{
				test=true;
			}else if(i==20)
			{
			 	test=true;
			}else
			{
				inputData[i]=holder;
				i++;
			}
			
		}
		inFile.close();	
		
		return i;
	}
	
	/************************************************************************
	*Function sortFile ||this function sorts the data aquired by readFile	*
	*and uses an improved bubble sort to sort them									*
	*Pre:inputData Array Post:returns a sorted array with the filenames				*
	*************************************************************************/
	public static String[] sortFile(String[] inputData,
											  int ct)
	{
		int lastPos;
		int index;
		String temp;
		
		
		for(lastPos=ct; lastPos>=0; lastPos--)
		{
			for(index=0;index<ct;index++)
			{
								
				if(index+1!=20&&inputData[index+1]!=null&&inputData[index].compareTo(inputData[index+1])>0)
				{
					temp=inputData[index];
					inputData[index]=inputData[index+1];
					inputData[index+1]=temp;
					
				}
				
			}
		}
	return inputData;
	}
	/************************************************************************
	*Function printToFile ||this function prints the sorted array to a file	*
	*																								*
	*Pre:SortedList array Post:none														*
	*************************************************************************/
	public static void printToFile(String[] sortedList,
											 String[] fileNames,
											 int ct)throws IOException
	{
		PrintWriter outFile=
						new PrintWriter(fileNames[1]+".txt");
		int index=0;
		
		for(index=0;index<ct;index++)
		{
			
			outFile.println(index+"  "+sortedList[index]);//prints the sorted array to a file
			
		}
		outFile.close();
	}
	/************************************************************************
	*Function searchList ||function Searches list for user inputted word		*
	*																								*
	*Pre:SortedList array Post:none														*
	*************************************************************************/
	public static void searchList(String[] sortedList,
											int ct)
	{
		String input;
		input=JOptionPane.showInputDialog("Please enter a word to search for, or stop to stop");
		
		
		
		while(!input.equalsIgnoreCase("stop"))
		{
			
			int first=0;
			int last=ct;
			int position=-1;
			boolean found=false;
			int middle;
			
			
			middle=(first+last)/2;
			
			while(!found&&first<last)
			{
				middle=(first+last)/2;
				if(sortedList[middle].equalsIgnoreCase(input))
				{
					found=true;
					position=middle; 
				}else if(sortedList[middle].compareToIgnoreCase(input)>0)
				{
					last=middle-1;
				}else
				{
					first=middle+1;
				}
			}
			JOptionPane.showMessageDialog(null,input+" found at position "+position); 
			input=JOptionPane.showInputDialog("Please enter a word to search for, or stop to stop");	
		}
	}
}

here is my code as it stands now, I was doing some final test and noticed that it can't seem to find object in position 0 every other array location works fine, but if I look for the string in 0 it returns -1 which means not found, any ideas?

[lenois]

tested middle, and the problem seems to be that middle never gets below 1
nevermind, it works if i set last to middle, although I imagine there is a better way to do it.