add solutions for hw7 (markup) and tests

java/markup/ListItem.java

@@ -0,0 +1,26 @@
+package markup;
+
+import java.util.List;
+
+public class ListItem {
+    private final List<ListItemContent> elements;
+
+    public ListItem(List<ListItemContent> elements) {
+        this.elements = elements;
+    }
+
+    public void toHtml(StringBuilder sb) {
+        sb.append("<li>");
+        for (ListItemContent element : elements) {
+            element.toHtml(sb);
+        }
+        sb.append("</li>");
+    }
+
+    public void toTex(StringBuilder sb) {
+        sb.append("\\item ");
+        for (ListItemContent element : elements) {
+            element.toTex(sb);
+        }
+    }
+}