Error CS1519

Trying to create a collision wall, where I can enter through one side, but can't go through another one I'm Getting Error CS1519, I can fix it by adding a " ; ", on the end of this line > GameObject.GetComponent But it creates a new error, I'm really new to this, so explaining why the error is here, and how should I type the script, would be blessful.

using UnityEngine; using System.Collections;

public class CollisionWall : MonoBehaviour {

 GameObject.GetComponent<BoxCollider>

 // Update is called once per frame
     void update() {

     // Makes the Wall a non colision object.
     if (Input.GetKey (KeyCode.A)) {
         BoxCollider2D.enabled = false;
         Debug.Log("This is an Illusion");
         
     }



     else {
         BoxCollider2D.enabled = true;
         Debug.Log("This is a WALL");
     }

} }