1. CIS 234: More File Input & Output Dr. Ralph D. Westfall May, 2007

2. Formatted File Data when do we need to know how many bytes are in different variable types? file data is a stream of bytes, which can be in different formats, including char (2 bytes per character in Unicode) non-character data e.g., int (4 bytes), double (8 bytes), boolean (1 byte)

3. Formatted File Data - 2 Java has classes for handling different types of (non-character) formatted data DataInputStream for reading DataOutputStream for writing can create members of these classes by passing File[Input or Output]Stream objects to the constructors also known as "chaining"

4. Formatted File Data - 3 creating output and input streams DataOutputStream out; // declare object out = new DataOutputStream (new FileOutputStream("myfile.txt")); // 2nd object created as argument to 1st DataInputStream inputs; inputs = new DataInputStream (new FileInputStream("myfile.txt"))

5. Writing Formatted Data out.writeChar('c'); //writes char c as int //A = 65, a = 97, etc. out.writeChars(str); // uses size of String //writes String characters as ints out.writeUTF(str); //writes String str // 1 st 2 bytes = length of String

6. Writing Formatted Data - 2 out.write(7); //writes an int (4 bytes) out.writeDouble(1.0); //double (8 bytes) out.writeLong(796342L); //long (8 bytes) out.writeBoolean(true);//boolean (1 byte) // usually write variables, not literals // why is number of bytes important?

7. Reading Formatted Data inputs.readChar(); //reads a char as int //no readChars method //why not? (see below) String name = inputs.readUTF(); //reads length of String, and then reads //that number of characters into a String

8. Reading Formatted Data - 2 byte w[] = new byte[1]; //array of bytes w=inputs.read(); // reads 1 byte int x=inputs.readInt(); // reads 4 bytes double y=inputs.readDouble(); // reads 8 bytes boolean z=inputs.readBoolean(); // reads 1 byte

9. Sequential vs. Random Access sequential access means read or write from start of file, one byte at a time random access means starting anywhere in file at start, at end, or anywhere in between random access also known as direct access makes it possible to change part of data without writing the whole file again

10. Random Access Java works with streams rather than records, so access is based on bytes rather than records if each "record" has an identifiable number of bytes, can handle as records RandomAccessFile class can be either r (read only) or rw (read and write) based on argument when opened

11. Random Access - 2 use seek() method to go to location where need to read or write int c; RandomAccessFile inFile = new RandomAccessFile("datafile.txt", "r"); // read only inFile.seek(5);// count starts at 0 c = inFile.readChar(); // reads 6 th char

12. Review How many bytes are in a file for each character? int? double? You also need to know the ____ to read diverse types of data from a file. what doe Java provide to help write programs that read or write data?

13. Review - 2 what does sequential access mean? give an example of sequential access? what does random access mean? what is the advantage of random access?