Mouse Click or Finger tap only on either game objects or UI objects

When facing the situation that we want the mouse click and finger tap can happened only on either game objects or UI items. Here is how:

using UnityEngine.EventSystems;

private void MouseInput() {
  if (Input.GetButtonDown("Fire1")) {

    if (!EventSystem.current.IsPointerOverGameObject()) {
      Debug.Log(Input.mousePosition);
      Vector3 pz = Camera.main.ScreenToWorldPoint(Input.mousePosition);
      pz.z = 0;

      planetSpawner.ReleasePlanet(pz.x);
    }
  }
}

EventSystem.current.IsPointerOverGameObject() determines whether the current click point in happened on an UI item or not.