Component

using UnityEngine;

public class ComponentBasics : MonoBehaviour
{
  // Cache: fetch the component once, not every frame
  private Rigidbody _rb;
  private Collider  _col;
  private Renderer  _renderer;

  void Awake()
  {
      _rb       = GetComponent<Rigidbody>();
      _col      = GetComponent<Collider>();
      _renderer = GetComponent<Renderer>();
  }

  void Start()
  {
      // Null-check before use (safe)
      if (_rb != null) _rb.mass = 2f;

      _renderer.enabled = false; // hide the object
      _col.enabled      = false; // disable collisions
  }

  public void MakeInvincible()
  {
      // Disable the AI script (do not remove the component)
      EnemyAI ai = GetComponent<EnemyAI>();
      if (ai != null) ai.enabled = false;
  }
}

using UnityEngine;

// Interface: a contract for any component that can take damage
public interface IDamageable
{
  void TakeDamage(int amount);
}

// Health component: only manages HP, knows nothing about combat
public class Health : MonoBehaviour, IDamageable
{
  [SerializeField] private int maxHP = 100;
  private int _currentHP;

  void Awake() => _currentHP = maxHP;

  public void TakeDamage(int amount)
  {
      _currentHP -= amount;
      if (_currentHP <= 0) Destroy(gameObject);
  }
}

// Bullet component: deals damage without knowing Health exists
public class Bullet : MonoBehaviour
{
  [SerializeField] private int damage = 25;

  void OnCollisionEnter(Collision col)
  {
      // Ask: does this object implement IDamageable? → loose coupling
      col.gameObject.GetComponent<IDamageable>()?.TakeDamage(damage);
      Destroy(gameObject);
  }
}