1. 构造函数
2. LinkedHashMap
3. from
4. fromEntries
5. fromIterable
6. fromIterables
7. identity
8. of
9. 属性
10. entries
11. hashCode
12. isEmpty
13. isNotEmpty
14. keys
15. length
16. runtimeType
17. values
18. 方法
19. addAll
20. addEntries
21. cast
22. clear
23. containsKey
24. containsValue
25. forEach
26. map
27. noSuchMethod
28. putIfAbsent
29. remove
30. removeWhere
31. toString
32. update
33. updateAll
34. 运算符
35. operator ==
36. operator []
37. operator []=