Visitor Pattern

VisitorPatternExample.java

import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class VisitorPatternExample {
	public static void main(String[] args) {
		List<String> list = new ArrayList<String>();
		//list.add("java");
		list.add("pdf");
		list.add("html");
		
		list.forEach(file -> {
			FileOperator head = new Head();
			FileUtil.fileIdentifier(file).doFileOperation(head);
		});
	}
}

//Visitable
interface ReadableFile {
	public String readNextLine();
	public void doFileOperation(FileOperator operator);
}

class PdfFile implements ReadableFile {

	PdfFile(String fileName) {
		// Create instance of File
	}

	public String readNextLine() {
		return "Reading line from a PDF";
	}

	@Override
	public void doFileOperation(FileOperator operator) {
		operator.processPdfFile(this);
	}

	public boolean isSecure() {
		return false;
	}
}

class HtmlFile implements ReadableFile {

	HtmlFile(String fileName) {
		// Create instance of File
	}

	public String readNextLine() {
		return "Reading line from a HTML";
	}
	
	@Override
	public void doFileOperation(FileOperator operator) {
		operator.processHtmlFile(this);
	}
}

interface FileOperator{
	public void processPdfFile(PdfFile file);
	public void processHtmlFile(HtmlFile file);
}

class Head implements FileOperator{
	
	public void operation(PdfFile file) {
		file.readNextLine();
	}

	@Override
	public void processPdfFile(PdfFile file) {
		if(file.isSecure()){
			System.out.println("Can't read secure file");
		}else{
			System.out.println(file.readNextLine());
		}
	}

	@Override
	public void processHtmlFile(HtmlFile file) {
		System.out.println(file.readNextLine());
	}


}

class FileUtil {
	public static ReadableFile fileIdentifier(String fileName) {
		if (fileName.toString().contains("pdf"))
			return new PdfFile(fileName);
		else if (fileName.toString().contains("html"))
			return new HtmlFile(fileName);
		return null;
	}

}