# Java IO: Byte & Char Arrays

Byte and char arrays are often used in Java to temporarily store data internally in an application. As such arrays are also a common source or destination of data. You may also prefer to load a file into an array, if you need to access the contents of that file a lot while the program is running. Of course you can access these arrays directly by indexing into them. But what if you have a component that is designed to read some specific data from an `InputStream` or `Reader` and not an array?

### Reading Arrays via InputStream or Reader

To make such a component read from the data from an array, you will have to wrap the byte or char array in an [`ByteArrayInputStream`](https://jenkov.com/tutorials/java-io/bytearrayinputstream.html) or [`CharArrayReader`](https://jenkov.com/tutorials/java-io/chararrayreader.html). This way the bytes or chars available in the array can be read through the wrapping stream or reader.

Here is a simple example:

```
byte[] bytes = new byte[1024];

//write data into byte array...

InputStream input = new ByteArrayInputStream(bytes);

//read first byte
int data = input.read();
while(data != -1) {
    //do something with data

    //read next byte
    data = input.read();
}
```

To do the same with a char array is pretty analogous to this example. Just wrap the char array in a `CharArrayReader` and you are good to go.

### Writing to Arrays via OutputStream or Writer

It is also possible to write data to an [`ByteArrayOutputStream`](https://jenkov.com/tutorials/java-io/bytearrayoutputstream.html) or [`CharArrayWriter`](https://jenkov.com/tutorials/java-io/chararraywriter.html). All you have to do is to create either a `ByteArrayOutputStream` or `CharArrayWriter`, and write your data to it, as you would to any other stream or writer. Once all the data is written to it, simply call the method `toByteArray()` or `toCharArray`, and all the data written is returned in array form.

Here is a simple example:

```
ByteArrayOutputStream output = new ByteArrayOutputStream();

output.write("This text is converted to bytes".getBytes("UTF-8"));

byte[] bytes = output.toByteArray();
```

To do the same with a char array is pretty analogous to this example. Just wrap the char array in a `CharArrayWriter` and you are good to go.