Byte Array Output Stream in Java - ByteArrayOutputStream

ByteArrayOutputStream is an implementation of an output stream that uses a byte array as the destination. ByteArrayOutputStream has two constructors, shown here:

ByteArrayOutputStream( )
ByteArrayOutputStream(int numBytes)

In the first form, a buffer of 32 bytes is created. In the second, a buffer is created with a size equal to that specified by numBytes. The buffer is held in the protected buf field of ByteArrayOutputStream. The buffer size will be increased automatically, if needed. The number of bytes held by the buffer is contained in the protected count field of ByteArrayOutputStream.

The following example demonstrates ByteArrayOutputStream:

// Demonstrate ByteArrayOutputStream.
import java.io.*;
class ByteArrayOutputStreamDemo {
public static void main(String args[]) throws IOException {
ByteArrayOutputStream f = new ByteArrayOutputStream();
String s = "This should end up in the array";
byte buf[] = s.getBytes();
f.write(buf);
System.out.println("Buffer as a string");
System.out.println(f.toString());
System.out.println("Into array");
byte b[] = f.toByteArray();
for (int i=0; i<b.length; i++) {
System.out.print((char) b[i]);
}
System.out.println("\\nTo an OutputStream()");
OutputStream f2 = new FileOutputStream("test.txt");
f.writeTo(f2);
f2.close();
System.out.println("Doing a reset");
f.reset();
for (int i=0; i<3; i++)
f.write('X');
System.out.println(f.toString());
}
}

When you run the program, you will create the following output. Notice how after the call to reset(), the three X's end up at the beginning.

Buffer as a string
This should end up in the array
Into array
This should end up in the array
To an OutputStream()
Doing a reset
XXX

This example uses the writeTo() convenience method to write the contents of f to test.txt. Examining the contents of the test.txt file created in the preceding example shows the result we expected:

This should end up in the array