FILE I/O Starring: Scanner Co-Starring: useDelimiter

1. FILE I/O Starring: Scanner Co-Starring: useDelimiter

2. LECTURE: FILE I/O Objective: Learn how to process data files, one line at a time, one field at a time. Read from a file and Write to a file. Use Scanner and PrintWriter classes for file processing.

3. Resources: Lambert Fundamentals, 3rd Edition p.127-129 & 74-76 Java 1.5 Program Design p.266-271

4. Processing files is a central element in robust application development. We will learn the Java way of file processing and then learn how to use predefined classes ( Scanner and File ) to make file processing much simpler.

5. The sample project, File IO.java, has static functions that illustrate file processing using the following options: 1. read a file one line at a time 2. write a new file 3. read a file one word at a time

6. Initial Steps: Create an Instance of the File class that allows you to hold the information about the file you wish to process // Create an Instance of the File Class // java.io File file = new File("file.txt");

7. PUT THE TEXT FILE (.txt) IN THE PROJECT FOLDER !!! Create an Instance of the Scanner class that allows you to PROCESS the file This step also opens the file // Create an Instance of the Scanner Class and // ASSOCIATE it with the FILE // To read in the fields of the FILE // OPENS the FILE "file.txt" Scanner scanner = new Scanner(file); // Create an Instance of the PrintWriter Class to WRITE out // an FILE PrintWriter pw = new PrintWriter(file);

8. Read a file one line at a time: // read in a file one line at a time // 1. read a file one line at a time ---- //DEFAULT WHITESPACE DELIMITER while (scanner.hasNext()) { System.out.println(scanner.nextLine()); } scanner.close();

9. Read a file one word at a time: //USE the useDelimeter Method of the Scanner //class to determine what constitutes a new word scanner = new Scanner(file); scanner.useDelimiter(","); while (scanner.hasNext()) { System.out.println(scanner.next()); } scanner.close();

10. You can also read in data as a number or a character: System.out.println("xxx" + scanner.nextLine()); // String; uses new line as a delimiter System.out.println(scanner.next()); // String; uses //space as delimiter by default System.out.println(scanner.nextInt() + 1); // int System.out.println(scanner.nextDouble() * 2); // // double System.out.println(scanner.next().charAt(0)); // //nextChar()

11. Write out to a FILE: // 3. write a new file // Create an Instance of the PrintWriter Class to WRITE // out an FILE file = new File("fileout.txt"); PrintWriter pw = new PrintWriter(file); pw.println("NEW LINE FIRST IN OUT FILE"); pw.println("NEW LINE SECOND IN OUT FILE"); pw.println("20 40 56 45"); pw.print("34,"); pw.print("72,"); pw.close();

12. Projects: Process Numbers in a File Unique Name Merge Correct Answers Modify Student File Average Student Answers Create a Writer Class MyTutor AN ELECTRONIC QUIZ FOLLOWS