[learning notes] Lombok's @builder annotation

First of all, I need to understand Builder Pattern ：

Define a User class ：

public class User {
    

  private String firstName;
  private String lastName;

  User(String firstName, String lastName) {
    
    this.firstName = firstName;
    this.lastName = lastName;
  }

  public static Builder builder() {
    
      return new Builder();
  }

  public static class Builder {
    

    String firstName;
    String lastName;

    Builder firstName(String value) {
    
        this.firstName = value;
        return this;
    }

    Builder lastName(String value) {
    
        this.lastName = value;
        return this;
    }

    public User build() {
    
        return new User(firstName, lastName);
    }
  }
}

Can be called in a chain way User Property of ：

User user = User.builder()
      .firstName("san")
      .lastName("zhang")
      .build();

The reason why it can be called in a chain is because User.Builder Class firstName() and lastName() Method returns all of Builder object .

and @Builder The use of annotations can greatly simplify the code ：

@Builder
public class User {
    
    private String firstName;
   private String lastName;
}

When used, it is the same as before ：

User user = User.Build()
      .firstName("san")
      .lastName("zhang")
      .build();