Attach additional responsibilities or functions to an object dynamically or statically. Also known as Wrapper.

Where to use & benefits


A JScrollPane object can be used to decorate a JTextArea object or a JEditorPane object. A window can be decorated with different borders like BevelBorder, CompoundBorder, EtchedBorder TitledBorder etc. These border classes working as decorators are provided in Java API.

Decorator pattern can be used in a non-visual fashion. For example, BufferedInputStream, DataInputStream, and CheckedInputStream are decorating objects of FilterInputStream class. These decorators are standard Java API classes.

To illustrate a simple decorator pattern in non-visual manner, we design a class that prints a number. We create a decorator class that adds a text to the Number object to indicate that such number is a random number. Of course we can subclass the Number class to achieve the same goal. But the decorator pattern provides us an alternative way.

import java.util.Random;
class Number {
   public void print() {
       System.out.println(new Random().nextInt());

class Decorator {
    public Decorator() {
        System.out.print("Random number: ");//add a description to the number printed
        new Number().print();

class SubNumber extends Number{
    public SubNumber() {
       System.out.print("Random number: ");

class Test {
    public static void main(String[] args) {
        new Decorator();
        new SubNumber();

 C:\ Command Prompt
C:\> java Test
Random number: 145265744
Random number: 145265755

Recap: The Number class just produces a random number. We use Decorator and SubNumber classes to attach or add a description to the random number which is produced by Number class. This is how Decorator pattern works.

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