## 强制类型转换
Java 中所有的强转，都依赖于等于或者put赋值时，右边实际指向的类型 与 强转类型之间的继承关系，如果强转的类型间没有父子关系（null 是一切人的兄弟），就会出 ClassCastException
```java
Object i= null;
System.out.println((Integer) i);
Object i= "string";
System.out.println((Integer) i);
```
上面的不会抛空指针，只输出一个 null
下面的会抛 `java.lang.ClassCastException`
### 那么基础类型的父子关系是啥？
```mermaid
graph BT
A[byte] --> B[short]
B --> C[int]
C --> D[long]
D --> E[float]
E --> F[double]
G[char] --> C
G --> D
G --> E
G --> F
H[boolean] --> I[不参与数值转换]
style A fill:#f9f,stroke:#333,stroke-width:2px
style B fill:#fcc,stroke:#333,stroke-width:2px
style C fill:#cfc,stroke:#333,stroke-width:2px
style D fill:#ccf,stroke:#333,stroke-width:2px
style E fill:#fcf,stroke:#333,stroke-width:2px
style F fill:#cff,stroke:#333,stroke-width:2px
style G fill:#ffc,stroke:#333,stroke-width:2px
style H fill:#f99,stroke:#333,stroke-width:2px
style I fill:#ddd,stroke:#333,stroke-width:2px
```