table of Contents
Fourth, the connection between the two
1. Concept
Value type: store the value directly, store its value on the stack
Application type: store a reference to its value, store an address on the stack, store a value on the heap
Two, data type
3. Comparison of the two
|
|
Value type |
Reference type |
| source |
Inherited from System.ValueType |
Inherited from System.Object |
| use |
Represents actual data |
Represents a pointer or reference to data stored in the memory heap |
| Data storage location |
Stored in the memory stack |
Stored in the heap of memory, and only the address of the object in the heap is stored in the memory unit |
| Variable storage type |
Store the actual data directly |
The address where the data is stored, that is, the reference of the object |
| Save location |
The variable directly saves the value of the variable in the stack |
Variables store the address of the actual data in the stack, and store the actual data in the heap |
| Inheritance |
Sealed, can not be used as any other type of base class, single inheritance or multiple inheritance interface |
Generally inherited |
| variable |
Can not be Null, the value type will be automatically initialized to a value of 0 |
By default, it is created as a Null value, which means that it points to the reference address of any managed heap. Operations on a reference type with a value of Null will throw a NullReferenceException exception |
Fourth, the connection between the two
Value types and reference types can be converted to each other, that is, boxing and unboxing operations:
Boxing occurs when a value type is converted to a reference type, and a data item (copy) is automatically copied from the stack to the heap.
int i = 8;
object o = i; // 装箱 // 首先在堆中开辟出一片区域，再将 i 的一个副本放在该区域中。
// 所有引用都必须引用堆上的对象
Unboxing occurs when a reference type is converted to a value type, and a data item (copy) is automatically copied from the heap to the stack.
int i = 8;
object o = i; // 装箱
i = (int)o; // 拆箱 // 此处使用强制类型转换（cast）supplement:
Managed heap: It is the basis of automatic memory management in CLR (Common Language Database). When a new process is initialized, a contiguous area of address space is reserved for the process at runtime. This reserved address space is called the managed heap.