for why we use FilterOutputStream in java

for why we use FilterOutputStream in java , pls explain wt a simple programme
and some material get knowledege abt that
thanks in advance

The FilterOutputStream class is the superclass of all of the output stream classes that filter output. Each of the subclasses of FilterOutputStream works by wrapping an existing output stream, called the underlying output stream, and providing additional functionality. The methods of FilterOutputStream simply override the methods of OutputStream with versions that call the corresponding methods of the underlying stream.

FilterOutputStream cannot be instantiated directly; it must be subclassed. An instance of one of the subclasses of FilterOutputStream is constructed with another OutputStream object. The methods of a subclass of FilterOutputStream should override some methods in order to extend their behavior or provide some sort of filtering.
public class java.io.FilterOutputStream extends java.io.OutputStream {
// Variables
protected OutputStream out;
// Constructors
public FilterOutputStream(OutputStream out);
// Instance Methods
public void close();
public void flush();
public void write(int b);
public void write(byte[] b);
public void write(byte[] b, int off, int len);
}