What is data file in java

Data Streams

Data streams support binary I/O of primitive data type values ( boolean , char , byte , short , int , long , float , and double ) as well as String values. All data streams implement either the DataInput interface or the DataOutput interface. This section focuses on the most widely-used implementations of these interfaces, DataInputStream and DataOutputStream .

The DataStreams example demonstrates data streams by writing out a set of data records, and then reading them in again. Each record consists of three values related to an item on an invoice, as shown in the following table:

Order in record	Data type	Data description	Output Method	Input Method	Sample Value
1	double	Item price	DataOutputStream.writeDouble	DataInputStream.readDouble	19.99
2	int	Unit count	DataOutputStream.writeInt	DataInputStream.readInt	12
3	String	Item description	DataOutputStream.writeUTF	DataInputStream.readUTF	«Java T-Shirt»

Let’s examine crucial code in DataStreams . First, the program defines some constants containing the name of the data file and the data that will be written to it:

static final String dataFile = "invoicedata"; static final double[] prices = < 19.99, 9.99, 15.99, 3.99, 4.99 >; static final int[] units = < 12, 8, 13, 29, 50 >; static final String[] descs = < "Java T-shirt", "Java Mug", "Duke Juggling Dolls", "Java Pin", "Java Key Chain" >;

Then DataStreams opens an output stream. Since a DataOutputStream can only be created as a wrapper for an existing byte stream object, DataStreams provides a buffered file output byte stream.

out = new DataOutputStream(new BufferedOutputStream( new FileOutputStream(dataFile)));

DataStreams writes out the records and closes the output stream.

The writeUTF method writes out String values in a modified form of UTF-8. This is a variable-width character encoding that only needs a single byte for common Western characters.

Now DataStreams reads the data back in again. First it must provide an input stream, and variables to hold the input data. Like DataOutputStream , DataInputStream must be constructed as a wrapper for a byte stream.

in = new DataInputStream(new BufferedInputStream(new FileInputStream(dataFile))); double price; int unit; String desc; double total = 0.0;

Now DataStreams can read each record in the stream, reporting on the data it encounters.

try < while (true) < price = in.readDouble(); unit = in.readInt(); desc = in.readUTF(); System.out.format("You ordered %d" + " units of %s at $%.2f%n", unit, desc, price); total += unit * price; >> catch (EOFException e)

Notice that DataStreams detects an end-of-file condition by catching EOFException , instead of testing for an invalid return value. All implementations of DataInput methods use EOFException instead of return values.

Also notice that each specialized write in DataStreams is exactly matched by the corresponding specialized read . It is up to the programmer to make sure that output types and input types are matched in this way: The input stream consists of simple binary data, with nothing to indicate the type of individual values, or where they begin in the stream.

DataStreams uses one very bad programming technique: it uses floating point numbers to represent monetary values. In general, floating point is bad for precise values. It’s particularly bad for decimal fractions, because common values (such as 0.1 ) do not have a binary representation.

The correct type to use for currency values is java.math.BigDecimal . Unfortunately, BigDecimal is an object type, so it won’t work with data streams. However, BigDecimal will work with object streams, which are covered in the next section.

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You asked: What is data file in Java?

There are classes specifically meant for reading character streams such as Reader and Writer. Before an application can use a data file, it must open the file. A Java application opens a file by creating an object and associating a stream of bytes with that object.

How write data file in Java?

Java FileWriter Example

What does file () do in Java?

Java File class represents the files and directory pathnames in an abstract manner. This class is used for creation of files and directories, file searching, file deletion, etc. The File object represents the actual file/directory on the disk.

What is URL in Java?

The Java URL class represents an URL. URL is an acronym for Uniform Resource Locator. It points to a resource on the World Wide Web. … A URL contains many information: Protocol: In this case, http is the protocol.

What is the purpose of data files?

A data file is a computer file which stores data to be used by a computer application or system, including input and output data. A data file usually does not contain instructions or code to be executed (that is, a computer program). Most of the computer programs work with data files.

What are the types of data files?

Top 6 Types of Data Files Used in any Information System | MIS

• Data File Type # 1. Work File:
• Data File Type # 2. Master File:
• Data File Type # 3. Audit File:
• Data File Type # 4. Transaction File:
• Data File Type # 5. Back Up or Security File:
• Data File Type # 6. History Files:

Which is called the data file?

The term may refer to a computer file that contains any type of data, including a word processing document or spreadsheet. … An electronic file containing the work created with a computer program. The contents of a data file are information in text or graphic format.

How do you write data to a file?

To write data into a file using FileOutputStream class is shown in the following example. It also requires to create the object of the class with the filename to write data into a file. Here, the string content is converted into the byte array that is written into the file by using the write() method.

What is Randomaccessfile in Java?

This class is used for reading and writing to random access file. A random access file behaves like a large array of bytes. If end-of-file is reached before the desired number of byte has been read than EOFException is thrown. … It is a type of IOException.

How do I save a file in Java?

1. Create class CrunchifyReadWriteUtilityForFile.java.
2. Create private inner class CrunchifyCompany with two fields. …
3. Create object crunchify inside main method.
4. Convert object to Gson so it will be saved to file.
5. Use method crunchifyWriteToFile to save data to file in Java.

Is a file Java?

The isFile() function is a part of File class in Java. This function determines whether the is a file or Directory denoted by the abstract filename is File or not. The function returns true if the abstract file path is File else returns false.

Why do we require files to store data in Java?

This requirement is achieved using File storage on a permanent storage device like a disk drive, CD ROM, pen drive etc. Java provides a library of classes to access this permanently stored information on files called FileIO or java.io.

How do you use another file in Java?

1. Create a file called Include.java. In this file, add this: public class Include
2. Create another file, say, User.java. In this file, put: import java.io.*; public class User extends Include

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File Handling in Java

Hi guys, welcome back. In this module, I will be discussing file handling in Java Programming. After reading this module, you will get to know file handling operations in Java. Let’s know about Java file handling without any further delay.

File Handling in Java

File handling in Java is an essential part of any programming language. Using files, a program can store data on a storage device. To perform various actions on a file, such as reading, writing, and so on, file handling is required.

file handling in Java is defined as reading from a file and writing to a file. We can use the File class in Java to create a file object. The package java.io contains a File class to work and handle different formats of files. If you want to use the File class, you need to create an object of the File class and provide the name of the file or pathname. Using file class we can access metadata of files such as file name, file size, permissions, type of file, etc.

// importing all the classes of java.io import java.io.*; class FileHandle < public static void main(String[] arr) < // an object of File class is created. File f=new File("demo.txt"); >>

Note: You can give an absolute pathname if you are not in the current working directory.

You can also use import java.io.File instead of using import java.io.* to import the File class in Java. Now, let’s know about streams because Java uses Streams to perform input-output (I/O) operations on a file.

What is a Stream in Java?

A stream in Java is a sequence of data. It is also defined as a sequence of bytes. It can be used to represent either an input source or a destination. The source and destination can be disk files, arrays, text files, etc. The input stream reads or retrieves data from a source, whereas the output stream writes data to a destination. There are two types of streams:

Byte stream in Java Programming

Byte Stream is used to perform read and write operations with byte data. A byte stream file handling in Java process is defined as when the given input is executed using byte data. There are many classes provided related to byte streams but the most often used classes are FileInputStream and FileOutputStream.

import java.io.*; public class FileHandle < public static void main(String []arr) throws IOException< FileInputStream fin=new FileInputStream("source_file.txt"); FileOutputStream fout=new FileOutputStream("destination_file.txt"); int character; while((character=fin.read())!=-1) < System.out.print((char)character); // writing to destination file fout.write((char)character); >// closing source_file.txt fin.close(); // closing destination_file.txt fout.close(); > >

In the above example, we are reading data from the source file and writing data to a destination. -1 indicates the end of the file. So, reading from the source file will be stopped when -1 is encountered.

Character stream in Java Programming

Character Stream in Java programming is used to perform read and write operations with character data. The file-handling process with a character stream is the process of executing input data with characters. There are many character stream classes available, but the most commonly used classes include FileWriter and FileReader.

Now, let’s discuss some of the File class methods in Java Programming.

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