Super simple start

src/main/java/net/minecraft/commands/builder/CommandBuilder.java

@@ -0,0 +1,28 @@
+package net.minecraft.commands.builder;
+
+public abstract class CommandBuilder {
+    private boolean finished;
+    private Runnable commandExecutor;
+
+    public void finish() {
+        if (finished) {
+            throw new IllegalStateException("Cannot finish() multiple times!");
+        }
+        if (commandExecutor == null) {
+            throw new IllegalStateException("Cannot finish() without a command executor!");
+        }
+        onFinish();
+        finished = true;
+    }
+
+    protected abstract void onFinish();
+
+    public CommandBuilder executes(Runnable runnable) {
+        this.commandExecutor = runnable;
+        return this;
+    }
+
+    public Runnable getCommandExecutor() {
+        return commandExecutor;
+    }
+}