Applied Programming/Files/Java

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files.java[edit]

/**
 * This program demonstrates file processing.
 * 
 * It creates a file, adds data to the file, displays the file, appends more data
 * to the file, displays the file, and then deletes the file.
 * 
 * It will not run if the file already exists.
 * 
 * Input:
 *     None
 * 
 * Output:
 *     A temporary file and file contents.
 * 
 * References:
 *     None
 */

import java.util.*;

/**
 * Runs main program logic.
 */
class Main
{
    public static void main(String[] args) 
    {
        String FILENAME = "~file.txt";
    
        if(fileExists(FILENAME))
        {
            System.out.println("File already exists.\n");
            System.exit(1)
        }

        createFile(FILENAME);
        readFile(FILENAME);
        appendFile(FILENAME);
        readFile(FILENAME);
        deleteFile(FILENAME);
    }
    
    /**
     * Creates filename and adds temperature data to the file.
     * 
     * @param filename
     * 
     * Catches IOException and terminates the program.
    */
    private static void createFile(String filename)
    {
        try
        {
            java.io.File file = new java.io.File(filename);
            java.io.BufferedWriter writer = 
                new java.io.BufferedWriter(new java.io.FileWriter(file));
            float c;
            float f;
            
            writer.write("C\tF\n");
            for(c = 0; c <= 50; c++)
            {
                f = c * 9 / 5 + 32;
                writer.write(c + "\t" + f + "\n");
            }
            writer.close();
        }
        catch(java.io.IOException e)
        {
            e.printStackTrace();
            System.exit(2);
        }
    }
    
    /**
     * Reads filename and displays each line.
     * 
     * @param filename
     * 
     * Catches IOException and terminates the program.
    */
    private static void readFile(String filename)
    {
        try
        {
            java.io.File file = new java.io.File(filename);
            java.io.BufferedReader reader = 
                new java.io.BufferedReader(new java.io.FileReader(file));
            String line;

            while(true)
            {
                line = reader.readLine();
                if (line == null)
                {
                    break;
                }
                System.out.println(line);
            }
            reader.close();
            System.out.println("");
        }
        catch(java.io.IOException e)
        {
            e.printStackTrace();
            System.exit(3);
        }
    }
    
    /**
     * Appends temperature data to filename.
     * 
     * @param filename
     * 
     * Catches IOException and terminates the program.
    */
    private static void appendFile(String filename)
    {
        try
        {
            java.io.File file = new java.io.File(filename);
            java.io.BufferedWriter writer = 
                new java.io.BufferedWriter(new java.io.FileWriter(file, true));
            float c;
            float f;
            
            for(c = 51; c <= 100; c++)
            {
                f = c * 9 / 5 + 32;
                writer.write(c + "\t" + f + "\n");
            }
            writer.close();
        }
        catch(java.io.IOException e)
        {
            e.printStackTrace();
            System.exit(4);
        }
    }
    
    /**
     * Deletes filename.
     * 
     * @param filename
    */
    private static void deleteFile(String filename)
    {
        java.io.File file;
        
        file = new java.io.File(filename);
        file.delete();        
    }
    
    /**
     * Determines whether or not filename exists.
     * 
     * @param filename
     * 
     * @return true or false
    */
    private static boolean fileExists(String filename)
    {
        java.io.File file;
        
        file = new java.io.File(filename);
        return file.exists();
    }
}

Try It[edit]

Copy and paste the code above into one of the following free online development environments or use your own Java compiler / interpreter / IDE.

See Also[edit]