implement cap table builder and reader

runtime/src/main/java/org/capnproto/BuilderCapabilityTable.java

@@ -0,0 +1,34 @@
+package org.capnproto;
+
+import java.util.ArrayList;
+import java.util.List;
+
+class BuilderCapabilityTable implements CapTableBuilder {
+
+    private final List<ClientHook> table = new ArrayList<>();
+
+    BuilderCapabilityTable() {
+    }
+
+    @Override
+    public ClientHook extractCap(int index) {
+        return table.get(index);
+    }
+
+    @Override
+    public int injectCap(ClientHook cap) {
+        int index = table.size();
+        table.add(cap);
+        return index;
+    }
+
+    @Override
+    public void dropCap(int index) {
+        table.set(index, null);
+    }
+
+    @Override
+    public ClientHook[] getTable() {
+        return table.toArray(new ClientHook[0]);
+    }
+}

runtime/src/main/java/org/capnproto/ReaderCapabilityTable.java

@@ -0,0 +1,17 @@
+package org.capnproto;
+
+import java.util.List;
+
+class ReaderCapabilityTable implements CapTableReader {
+
+    final List<ClientHook> table;
+
+    ReaderCapabilityTable(List<ClientHook> table) {
+        this.table = table;
+    }
+
+    @Override
+    public ClientHook extractCap(int index) {
+        return index < table.size() ? table.get(index) : null;
+    }
+}