add solutions for hw7 (markup) and tests

java/markup/AbstractMarkup.java

@@ -0,0 +1,35 @@
+package markup;
+
+import java.util.List;
+
+public abstract class AbstractMarkup implements MarkupElement {
+    protected final List<MarkupElement> elements;
+
+    public AbstractMarkup(List<MarkupElement> elements) {
+        this.elements = elements;
+    }
+
+    protected void toMarkdown(StringBuilder sb, String delimiter) {
+        sb.append(delimiter);
+        for (MarkupElement element : elements) {
+            element.toMarkdown(sb);
+        }
+        sb.append(delimiter);
+    }
+
+    protected void toHtml(StringBuilder sb, String tag) {
+        sb.append("<").append(tag).append(">");
+        for (MarkupElement element : elements) {
+            element.toHtml(sb);
+        }
+        sb.append("</").append(tag).append(">");
+    }
+
+    protected void toTex(StringBuilder sb, String command) {
+        sb.append(command).append("{");
+        for (MarkupElement element : elements) {
+            element.toTex(sb);
+        }
+        sb.append("}");
+    }
+}