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package net.coderodde.html.view;
/**
 * This abstract class defines the API for logical HTML view components, that 
 * may consist of other view components;
 * 
 * @author Rodion "rodde" Efremov
 * @version 1.6 (Mar 18, 2016)
 */
public abstract class HtmlViewComponent {
 @Override
 public abstract String toString();
}

HtmlViewContainer.java

package net.coderodde.html.view;
import java.util.ArrayList;
import java.util.List;
import java.util.Objects;
/**
 * This class defines the API for HTML elements that may contain other HTML
 * elements.
 * 
 * @author Rodion "rodde" Efremov
 * @version 1.6 (Mar 18, 2016)
 */
public abstract class HtmlViewContainer extends HtmlViewComponent {
 protected final List<HtmlViewComponent> components = new ArrayList<>();
 public void addHtmlViewComponent(HtmlViewComponent component) {
 Objects.requireNonNull(component, "The input component is null.");
 components.add(component);
 }
 public boolean containsHtmlViewComponent(HtmlViewComponent component) {
 Objects.requireNonNull(component, "The input component is null.");
 return components.contains(component);
 }
 public void removeHtmlViewComponent(HtmlViewComponent component) {
 Objects.requireNonNull(component, "The input component is null.");
 components.remove(component);
 }
 @Override
 public abstract String toString();
}

HtmlPage.java

package net.coderodde.html.view;
/**
 * This class is the top-level container of view components.
 * 
 * @author Rodion "rodde" Efremov
 * @version 1.6 (Mar 18, 2016)
 */
public class HtmlPage extends HtmlViewContainer {
 private final String title;
 public HtmlPage(String title) {
 this.title = title != null ? title : "";
 }
 @Override
 public String toString() {
 StringBuilder sb = new StringBuilder().append("<!DOCTYPE html>\n")
 .append("<html>\n")
 .append("<head>\n")
 .append("<title>")
 .append(title)
 .append("</title>\n")
 .append("</head>\n")
 .append("<body>\n");
 components.stream().forEach((component) -> {
 sb.append(component.toString());
 });
 return sb.append("</body>\n")
 .append("</html>").toString();
 }
}

DivComponent.java

package net.coderodde.html.view.support;
import net.coderodde.html.view.HtmlViewContainer;
/**
 * This class implements a {@code div} component.
 * 
 * @author Rodion "rodde" Efremov
 * @version 1.6 (Mar 18, 2016)
 */
public class DivComponent extends HtmlViewContainer {
 @Override
 public String toString() {
 StringBuilder sb = new StringBuilder("<div>\n");
 components.stream().forEach((component) -> {
 sb.append(component.toString());
 });
 return sb.append("</div>\n").toString();
 }
}

TableComponent.java

package net.coderodde.html.view.support;
import java.util.ArrayList;
import java.util.List;
import net.coderodde.html.view.HtmlViewComponent;
/**
 * This class represents the table component.
 * 
 * @author Rodion "rodde" Efremov
 * @version 1.6 (Mar 18, 2016)
 */
public class TableComponent extends HtmlViewComponent {
 private final int columns;
 public TableComponent(int columns) {
 checkColumnNumber(columns);
 this.columns = columns;
 }
 private final List<List<? extends HtmlViewComponent>> table = new ArrayList<>();
 public void addRow(List<HtmlViewComponent> row) {
 while (row.size() > columns) {
 row.remove(row.size() - 1);
 }
 table.add(row);
 }
 private void checkColumnNumber(int columns) {
 if (columns <= 0) {
 throw new IllegalArgumentException(
 "The number of columns must be a positive integer. " +
 "Received " + columns);
 }
 }
 @Override
 public String toString() {
 StringBuilder sb = new StringBuilder().append("<table>\n");
 for (List<? extends HtmlViewComponent> row : table) {
 sb.append("<tr>");
 for (HtmlViewComponent cell : row) {
 sb.append("<td>");
 sb.append(cell.toString());
 sb.append("</td>");
 }
 for (int i = row.size(); i < columns; ++i) {
 sb.append("<td></td>");
 }
 sb.append("</tr>\n");
 }
 return sb.append("</table>\n").toString();
 }
}

TextComponent.java

package net.coderodde.html.view.support;
import net.coderodde.html.view.HtmlViewComponent;
/**
 * This class represents a simple text.
 * 
 * @author Rodion "rodde" Efremov
 * @version 1.6 (Mar 18, 2016)
 */
public class TextComponent extends HtmlViewComponent {
 private String text; 
 public TextComponent() {
 this("");
 }
 public TextComponent(String text) {
 setText(text);
 }
 public void setText(String text) {
 this.text = text != null ? text : "";
 }
 public String getText() {
 return text;
 }
 @Override
 public String toString() {
 return text;
 }
}

Demo.java

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import net.coderodde.html.view.HtmlPage;
import net.coderodde.html.view.HtmlViewComponent;
import net.coderodde.html.view.support.DivComponent;
import net.coderodde.html.view.support.TableComponent;
import net.coderodde.html.view.support.TextComponent;
public class Demo {
 public static void main(String[] args) {
 HtmlPage page = new HtmlPage("FUNKEEH PAGE");
 DivComponent div1 = new DivComponent();
 DivComponent div2 = new DivComponent();
 div1.addHtmlViewComponent(new TextComponent("Hey yo!\n"));
 TableComponent table = new TableComponent(3);
 // Arrays.asList is immutable, so copy to a mutable array list.
 List<HtmlViewComponent> row1 = new ArrayList<>(
 Arrays.asList(new TextComponent("Row 1, column 1"),
 new TextComponent("Row 1, column 2"),
 new TextComponent("Row 1, column 3"),
 new TextComponent("FAIL")));
 List<HtmlViewComponent> row2 = new ArrayList<>(
 Arrays.asList(new TextComponent("Row 2, column 1"),
 new TextComponent("Row 2, column 2")));
 table.addRow(row1);
 table.addRow(row2);
 div2.addHtmlViewComponent(table);
 div2.addHtmlViewComponent(new TextComponent("Bye, bye!\n"));
 page.addHtmlViewComponent(div1);
 page.addHtmlViewComponent(div2);
 System.out.println(page);
 }
}

I don't think it is of any use, but I want to hear comments on the hierarchy aspect. Please, tell me anything that comes to mind.

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