Rust for Java Programmers | Rust 面向 Java 程序员

Smart Pointers: Beyond Single Ownership
智能指针：超越单一所有权

What you’ll learn: When Box, Rc, Arc, RefCell, and Mutex are needed, and how they compare to Java’s always-reference-based object model.
本章将学习： 什么时候该用 Box、Rc、Arc、RefCell、Mutex，以及它们和 Java 那种“对象默认全靠引用”模型有什么区别。

Difficulty: 🔴 Advanced
难度： 🔴 高级

Java developers are used to object references everywhere. Rust starts from direct ownership and only adds pointer-like wrappers when they are actually needed.
Java 开发者习惯了对象到处都是引用。Rust 则是先从直接所有权开始，只有真的需要时才引入带指针味道的包装类型。

Common Smart Pointers
常见智能指针

The Key Difference from Java
和 Java 的关键差异

In Java, shared references are the default. In Rust, shared ownership is a deliberate choice with a specific type.
在 Java 里，共享引用是默认状态；在 Rust 里，共享所有权必须通过专门类型显式表达。

Guidance
使用建议

• use plain values and references first
  优先从普通值和引用开始。
• add Box when recursive or heap-allocated layout is needed
  递归结构或需要稳定堆布局时，再加 Box。
• add Rc or Arc only when multiple owners are truly required
  只有真的存在多个 owner 时，再上 Rc 或 Arc。
• pair Arc with Mutex only when shared mutable state is unavoidable
  只有共享可变状态躲不过去时，才把 Arc 和 Mutex 配一起。

These types are powerful, but they are also signals that the ownership model has become more complex.
这些类型很好用，但它们同时也是信号：代码里的所有权关系已经开始变复杂了。