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Streams and File I/O

Streams and File I/O. October 23, 2013. 10.1 AN OVERVIEW OF STREAMS AND FILE I/O . A stream is a flow of data. The data might be characters, numbers, or bytes consisting of binary digits. If the data flows into your program, the stream is called an input stream.

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Streams and File I/O

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  1. Streams and File I/O October 23, 2013

  2. 10.1 AN OVERVIEW OF STREAMS AND FILE I/O • A stream is a flow of data. • The data might be characters, numbers, or bytes consisting of binary digits. • If the data flows into your program, the stream is called an input stream. • If the data flows out of your program, the stream is called an output stream.

  3. Stream

  4. Stream • A stream is an object that either • Delivers data from program to a destination, such as a file or the screen • Takes data from a source, such as a file or the keyboard, and delivers the data to program

  5. Text Files and Binary Files • All the data in any file is stored as bits – that is a long sequence of 0s and 1s. • Text file – bits are interpreted as sequence of characters • Binary file – all other file • Java program can read both text and binary files

  6. Text File and a Binary File Containing the Same Values

  7. 10.2 TEXT-FILE I/O • Creating/Writing to a Text File • Appending to a Text File • Reading from a Text File

  8. Creating/Writing to a Text File • Stream variable – reference to stream • Class PrintWriter in java.io connects a file to an output stream • Overwrites file contents

  9. LISTING 10.1: Writing Output to a Text File (1/2)

  10. LISTING 10.1: Writing Output to a Text File (2/2)

  11. Writing Output to a Text File

  12. Appending to a Text File • Append – write at the end of the file • Old content of the file will remain • PrintWriter does not have appropriate constructor • We need class FileOutputStream from java.io

  13. Reading from a Text File • Scanner class • Constructor of Scanner does not take a String argument as filename • Constructor of Scanner accepts an instance of File class • File has a constructor to take a String argument as filename

  14. LISTING 10.2:Reading from a Text File (1/3)

  15. LISTING 10.2:Reading from a Text File (2/3)

  16. Reading from a Text File (3/3)

  17. Additional Methods in the Class Scanner

  18. 10.3 TECHNIQUES FOR ANY FILE:The Class File • The class File provides a way to represent file names in a general way. • A string “treasure.txt” is just a string to Java • Class File create an object which Java recognize as a name of a file.

  19. LISTING 10.3 Reading a File Name and Then the File (1/2)

  20. LISTING 10.3 Reading a File Name and Then the File (2/2)

  21. Reading a File Name and Then the File

  22. Using Path Names (1/3) • When file and the program are in the same directory – we specify only filename • If they are in different location – we have to specify path name instead of filename • Full path name – complete path name starting from the root directory • Relative path name – path to the file starting from the current working directory

  23. Using Path Names (2/3)

  24. Using Path Names (3/3) • Java program accepts • Unix format path name in Unix, Windows • Windows format path name in Unix, Windows

  25. Some Methods in the Class File

  26. Check a text file for reading

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