简要回答网友的问题：

when 的用法包含着while，就是说when 的用法多于while。

1. 当谓语动词表达延续的动作时，用when和while均可：

When I was walking through the forest, a bear came out. =

While I was walking through the forest, a bear came out. 

2. 当谓语动词表达的动作是瞬间的不延续，或者突然发生时，只能用when，不可用while：

When I arrived at the station, the train had left.

When John came in Tom was sleeping.

Tom was sleeping when John came in. （网友的句子，与本句用法相同。when 表示“突然发生”，这时when 只可放在主句后，也有人认为when 是并列连词，引导并列分句）

notice 跟come in 一样，也是“瞬间动词”，不可与while 连用。