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File I/O in Java
What are Streams?
Stream is an object that allows flow of data between your program and I/O devices or some files.
Stream is an object that allows flow of data between your program and I/O devices or some files.
- They also called ASCII files.
- Can be read by human.
- Can move from one computer to other.
- Can read or write to them using text editors.
- Can be read only by programs.
- In java, binary files can move from one type of computer to another.
- Must read or write to them using only by a program.
A. Reading From A text file:
The two main stream classes for reading from a text file:
a. Using Scanner
Ex:
Ex:
//Opening an inputStream and convert the file name to FileInputStream object
Scanner inputStream = new Scanner(new FileInputStream("marks.txt"));
int counter = 0;
while (inputStream.hasNextInt()) { //Returns true if there is next int in the file
int number = inputStream.nextInt(); //Scans the next token of the input as an int.
System.out.println(number);
}
inputStream.close();Output:
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3b. Using BufferedReader
Ex:
Ex:
//The program opens the text file
BufferedReader inputStream = new BufferedReader(new FileReader("quots.txt")); //FileReader to convert the file name to object
String i= inputStream.readLine();
while (i!=null){
System.out.println(i);
i= inputStream.readLine();
}Output:
123 hello
1 23d I am on console!BufferedReader class has no constructor takes a file name as it's argument (We need to convert the file name to object).readLine and read.read method reads a single character, and returns an int that corresponds to the character you read.(You need to cast that int to get the character), ex:
char next = (char)inputStram.read();readLine method returns null and read method returns -1.Unlike class Scanner, the class BufferedReader has no
constructor to deal with numbers. You have to read the numbers as a string then convert the string to a numeric type, ex:
Integer.parseInt(); Double.pareDouble();
If there are multiple numbers in a single line:
a. Read the line using
b. Use
readLine()b. Use
StringTokenizer to decompose the string into tokens.B. Writing to a text file:
The class
Ex:
The class
PrintWriter is the preferred class to write to a text file.Ex:
//Opening the file
PrintWriter outputStream = new PrintWriter(new FileOutputStream("shahed.txt")); //use FileOutputStream to convert the file name to object
//writing to the file
outputStream.print("this line written from a java program");
//close the connection
outputStream.close();Output:
this line written from a java programFile class.
PrintWriter class has no constructor takes a file name as it's argument (We need to convert the file name to object).flush()
close() include an invocation of flush().PrintWriter outputStreamToAppend = new PrintWriter(new FileOutputStream("shahed.txt", true));In this way the old content will remain and the new content will place after the old content.
PrintWriter class throw FileNotFoundException and it indicates that file can't be created.The
File classFile class constructor takes a string name (Abstract name) and checks the properties if that name, ex exists methods checks if name is exists, and isDirectory() tests if the name the name of a directory.
ex:
File file = new File ("Fruits.txt");
if (!file.canRead()){
System.out.println("The file can not be read!")
}setReadOnly()canWrite()delete()getName()getPath()length()
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