Any differences between the three dependency injection methods?

Question

Is the third most common bean injection method? Any differences between the two?

• Bean Entering constructor parameters:

   public class Checkout {
      private final ShoppingCart cart;
  
      @Inject
      public Checkout(ShoppingCart cart) {
        this.cart = cart;
      }
  }
  

• Inserting an initializer method parameter:

  public class Checkout {
  
     private ShoppingCart cart;
  
     @Inject
     void setShoppingCart(ShoppingCart cart) {
        this.cart = cart;
     }
  }
  

• Field Insertion:

  public class Checkout {
     private @Inject ShoppingCart cart;
  }
  

Answer 1

An opinion based answer, but it seems that injection through the constructor is best for the following reasons.

• You can perform a null constructor check, which can lead to incorrect error handling elsewhere in your class.
• You can more easily inject mocks into your class for testing.
• You cannot forget to indicate the dependency.
• This is not like magic.

Answer 2

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