/ Design Patterns / Structural patterns / Decorator

Decorator Design Pattern in Java

Decorator - authenticate, input, encrypt, authenticate, decrypt, output

import java.io.*;

public class DecoratorStream {
  static BufferedReader in = new BufferedReader(new InputStreamReader(System.in));

  interface LCD {
    void write( String[] s );
    void read(  String[] s );
  }

  static class Core implements LCD {
    public void write( String[] s ) {
      System.out.print( "INPUT:    " );
      try {
        s[0] = in.readLine();
      } catch (IOException ex) { ex.printStackTrace(); }
    }
    public void read( String[] s ) {
      System.out.println( "Output:   " + s[0] );
  } }

  static class Decorator implements LCD {
    private LCD inner;
    public Decorator( LCD i ) { inner = i; }
    public void write( String[] s ) { inner.write( s ); }
    public void read(  String[] s ) { inner.read(  s ); }
  }

  static class Authenticate extends Decorator {
    public Authenticate( LCD inner ) { super( inner ); }
    public void write(  String[] s ) {
      System.out.print( "PASSWORD: " );
      try {
        in.readLine();
      } catch (IOException ex) { ex.printStackTrace(); }
      super.write( s );
    }
    public void read( String[] s ) {
      System.out.print( "PASSWORD: " );
      try {
        in.readLine();
      } catch (IOException ex) { ex.printStackTrace(); }
      super.read( s );
  } }

  static class Scramble extends Decorator {
    public Scramble( LCD inner ) { super( inner ); }
    public void write( String[] s ) {
      super.write( s );
      System.out.println( "encrypt:" );
      StringBuffer sb = new StringBuffer( s[0] );
      for (int i=0; i < sb.length(); i++)
        sb.setCharAt( i, (char) (sb.charAt( i ) - 5) );
      s[0] = sb.toString();
    }
    public void read( String[] s ) {
      StringBuffer sb = new StringBuffer( s[0] );
      for (int i=0; i < sb.length(); i++)
        sb.setCharAt( i, (char) (sb.charAt( i ) + 5) );
      s[0] = sb.toString();
      System.out.println( "decrypt:" );
      super.read( s );
  } }

  public static void main( String[] args ) {
    LCD stream = new Authenticate( new Scramble( new Core() ) );
    String[] str = { new String() };
    stream.write( str );
    System.out.println( "main:     " + str[0] );
    stream.read( str );
} }

Output

PASSWORD: secret
INPUT:    the quick brown fox
encrypt:
main:     oc`xlpd^fe]mjrizajs
PASSWORD: secret
decrypt:
Output:   the quick brown fox

Code examples

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