Decorator Pattern in Java

package io.thecodeforge.java.patterns;

// Step 1: Define the component interface
interface TextProcessor {
    String process(String text);
}

// Step 2: Concrete component
class PlainTextProcessor implements TextProcessor {
    @Override
    public String process(String text) {
        return text;
    }
}

// Step 3: Abstract decorator — holds a reference to the wrapped component
abstract class TextProcessorDecorator implements TextProcessor {
    protected final TextProcessor wrapped;
    TextProcessorDecorator(TextProcessor wrapped) { this.wrapped = wrapped; }
}

// Step 4: Concrete decorators
class UpperCaseDecorator extends TextProcessorDecorator {
    UpperCaseDecorator(TextProcessor wrapped) { super(wrapped); }
    @Override public String process(String text) {
        return wrapped.process(text).toUpperCase(); // add before/after
    }
}

class TrimDecorator extends TextProcessorDecorator {
    TrimDecorator(TextProcessor wrapped) { super(wrapped); }
    @Override public String process(String text) {
        return wrapped.process(text.trim());  // modify input
    }
}

class PrefixDecorator extends TextProcessorDecorator {
    private final String prefix;
    PrefixDecorator(TextProcessor wrapped, String prefix) {
        super(wrapped);
        this.prefix = prefix;
    }
    @Override public String process(String text) {
        return prefix + wrapped.process(text);
    }
}

public class DecoratorDemo {
    public static void main(String[] args) {
        // Compose freely at runtime
        TextProcessor simple = new PlainTextProcessor();
        TextProcessor trimmed = new TrimDecorator(simple);
        TextProcessor upper   = new UpperCaseDecorator(trimmed);
        TextProcessor tagged  = new PrefixDecorator(upper, "[RESULT] ");

        System.out.println(tagged.process("  hello world  "));
        // [RESULT] HELLO WORLD
    }
}

package io.thecodeforge.java.patterns;

import java.io.*;
import java.util.zip.GZIPInputStream;

public class IODecorators {
    public static void main(String[] args) throws Exception {
        // Each wrapper adds behaviour without modifying the inner class:
        // FileReader: reads characters from a file
        // BufferedReader: adds buffering (reads in chunks, not char by char)
        // — both implement Reader

        try (BufferedReader reader = new BufferedReader(
                new FileReader("data.txt"))) {
            String line;
            while ((line = reader.readLine()) != null) {
                System.out.println(line);
            }
        }

        // Stack more decorators for more behaviour:
        // FileInputStream → GZIPInputStream → InputStreamReader → BufferedReader
        try (BufferedReader gzipReader = new BufferedReader(
                new InputStreamReader(
                    new GZIPInputStream(
                        new FileInputStream("data.gz"))))) {
            System.out.println(gzipReader.readLine());
        }
        // No class was modified — behaviour added by wrapping
    }
}