Java I/O – built in I/O classes

Introducing Java I/O

Java I/O stands for Java Input/Output. In the previous chapters, we were actually using Java’s I/O system but without knowing much about it. Java’s I/O system is very elaborate and it is not possible to discuss each and every API Java provides. We will discuss the basic and important APIs here, and it is your responsibility to explore more as a Java developer.

Java I/O system contains many built-in classes. We can classify the Java I/O into two categories as shown below.

Text based
File based

Java performs I/O operations through streams. An I/O stream is an abstraction that produces or consumes information. A stream is directly linked to a physical device using Java I/O system. All streams behave in the same manner to whatever device it is connected to. The implementation of I/O streams is done in java.io package.

The Byte Stream Classes

Byte streams are defined by two main abstract classes InputStream and OutputStream. InputStream defines common classes that consume byte input from devices whereas OutputStream defines classes to write a byte to devices. There are so many classes derived from these two streams, but they all work in the same manner. If you learn one class then you can easily understand the remaining.

Below is the list of Byte stream classes.

Byte Stream Class	Meaning
BufferedInputStream	Buffered input stream
BufferedOutputStream	Buffered output stream
ByteArrayInputStream	Input stream that reads from a byte array
ByteArrayOutputStream	Output stream that writes to a byte array
DataInputStream	An input stream that contains methods for reading the Java standard data types
DataOutputStream	An output stream that contains methods for writing the Java standard data types
FileInputStream	Input stream that reads from a file
FileOutputStream	Output stream that writes to a file
FilterInputStream	Implements InputStream
FilterOutputStream	Implements OutputStream
InputStream	Abstract class that describes stream input
ObjectInputStream	Input stream for objects
ObjectOutputStream	Output stream for objects
OutputStream	Abstract class that describes stream output
PipedInputStream	Input pipe
PipedOutputStream	Output pipe
PrintStream	Output stream that contains print() and println()
PushbackInputStream	Input stream that allows bytes to be returned to the stream
SequenceInputStream	Input stream that is a combination of two or more input streams that will be read sequentially, one after the other

The Character Stream

Character streams consume character data. They have two main abstract classes: Reader and Writer. We use Reader for input and Writer for output.

Below are the list of character stream classes.

Character Stream Class	Meaning
BufferedReader	Buffered input character stream
BufferedWriter	Buffered output character stream
CharArrayReader	Input stream that reads from a character array
CharArrayWriter	Output stream that writes to a character array
FileReader	Input stream that reads from a file
FileWriter	Output stream that writes to a file
FilterReader	Filtered reader
FilterWriter	Filtered writer
InputStreamReader	Input stream that translates bytes to characters
LineNumberReader	Input stream that counts lines
OutputStreamWriter	Output stream that translates characters to bytes
PipedReader	Input pipe
PipedWriter	Output pipe
PrintWriter	Output stream that contains print() and println()
PushbackReader	Input stream that allows characters to be returned to the input stream
Reader	Abstract class that describes character stream input
StringReader	Input stream that reads from a string
StringWriter	Output stream that writes to a string
Writer	Abstract class that describes character stream output

You can learn more information about Java I/O from Oracle Java help site.

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