Java IO reader and writer

Java IO's

Reader

and

Writer

work much like the

InputStream

and

OutputStream

with the exception that

Reader

and

Writer

are character based. They are intended for reading and writing text. The

InputStream

and

OutputStream

were byte based, remember?

Reader

The

Reader

is the baseclass of all

Reader

's in the Java IO API. Subclasses include a

BufferedReader

,

PushbackReader

etc.

Here is a simple example:

Reader reader = new FileReader();

int data = reader.read();
while(data != -1){
char dataChar = (char) data;
data = reader.read();
}

Notice, that while an

InputStream

returns one byte at a time, meaning a value between -128 and 127, the

Reader

returns a

char

at a time, meaning a value between 0 and 65535. This does not necessarily mean that the

Reader

reads two bytes at a time from the source it is connected to. It may read one or more bytes at a time, depending on the encoding of the text being read.

A

Reader

can be combined with an

InputStream

. If you have an

InputStream

and want to read characters from it, you can wrap it in an

InputStreamReader

. Pass the

InputStream

to the constructor of the

InputStreamReader

like this:

Reader reader = new InputStreamReader(inputStream);

In the constructor you can also specify what character set to use to decode the text etc. More on that in the text on

InputStreamReader

.

Writer

The

Writer

class is the baseclass of all

Writer

's in the Java IO API. Subclasses include

BufferedWriter

and

PrintWriter

among others.

Here is a simple example:

Writer writer = new FileWriter("c:\\data\\file-output.txt");

writer.write("Hello World Writer");
writer.close();

A

Writer

can be combined with an

OutputStream

just like

Readers

and

InputStream

's. Wrap the

OutputStream

in an

OutputStreamWriter

and all characters written to the

Writer

are passed on to the

OutputStream

. Here is how that looks:

Writer writer = new OutputStreamWriter(outputStream);

Combining Readers and Writers

Just like with streams,

Reader

's and

Writer

's can be combined into chains to achieve more interesting IO. It works just like combining the

Reader

with

InputStream

's or the

Writer

with

OutputStream

's. For instance, you can achieve buffering by wrapping a

Reader

in a

BufferedReader

, or a

Writer

in a

BufferedWriter

. Here are two such examples:

Reader reader = new BufferedReader(new FileReader(...));

Writer writer = new BufferedWriter(new FileWriter(...)