将初始对象添加到领域

public class User {
    private String id;
    private String name;
    private int age;

    private User(Builder builder) {
        this.id = builder.id;
        this.name = builder.name;
        this.age = builder.age;
    }

    public static class Builder {
        private String id;
        private String name;
        private int age;

        public Builder id(String id) {
            this.id = id;
            return this;
        }

        public Builder name(String name) {
            this.name = name;
            return this;
        }

        public Builder age(int age) {
            this.age = age;
            return this;
        }

        public User build() {
            return new User(this);
        }
    }
}

// 使用构建器创建用户对象
User user = new User.Builder()
    .id("123")
    .name("Alice")
    .age(30)
    .build();

public class Order {
    private String orderId;
    private List<OrderItem> items;

    // 其他属性和方法
}

public class OrderItem {
    private String itemId;
    private Product product;
    private int quantity;

    // 其他属性和方法
}

public class Product {
    private String productId;
    private String name;
    private double price;

    // 其他属性和方法
}