/ Design Patterns / Structural patterns / Decorator

Decorator Design Pattern in Java

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

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

class Core implements LCD {
    BufferedReader in = new BufferedReader(new InputStreamReader(System.in));

    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]);
    }
}

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);
    }
}

class Scramble extends Decorator {
    public Scramble(LCD inner) {
        super(inner);
    }

    public void write( String[] s ) {
        super.write(s);
        System.out.println("encrypt:");
        StringBuilder sb = new StringBuilder(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) {
        StringBuilder sb = new StringBuilder(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 class DecoratorDemo extends Decorator {
    BufferedReader in = new BufferedReader(new InputStreamReader(System.in));

    public DecoratorDemo(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);
    }

    public static void main(String[] args) {
        LCD stream = new DecoratorDemo(new Scramble(new Core()));
        String[] str = {""};
        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

Java Decorator in Java Decorator in Java Decorator in Java Decorator in Java
C++ Decorator in C++: Before and after Decorator in C++ Decorator in C++: Encoding and decoding layers of header/packet/trailer
PHP Decorator in PHP
Delphi Decorator in Delphi
Python Decorator in Python