git本地仓库，分支切换的问题

在本地创建的git仓库，在分支1中修改某文件，不提交，切换到分支2，结果在分支2中也能看到分支1中的
修改，并且可以在分支2中提交该修改。。。
不明白为啥会这样，分支之间的修改，应该是互相不可见的才对吧。
其实在切换分支之前，提交一下其实也没什么，但这样的特性总让人感觉不爽。

从下面的文章中找到了一个解决方法，那就是在分支1中，切换之前先git stash一下，它会把你的修改隐藏
起来，这样切换分支时就不会有问题。在其他分支修改完之后，回来可以通过git stash list看到你的隐藏记录，
并且通过git stash apply stash@{0}这样的方式把修改拿回来。
    http://www.cppblog.com/deercoder/archive/2011/11/13/160007.html

感觉以上链接的博主。

下面是一个实验过程：
mt@Mars:~/aaa$ ls
file
mt@Mars:~/aaa$ cat file
This is a file.
##创建两个新的分支，test1和test2
mt@Mars:~/aaa$ git branch test1
mt@Mars:~/aaa$ git branch test2
mt@Mars:~/aaa$ git branch
* master
  test1
  test2
mt@Mars:~/aaa$ git checkout test1
Switched to branch 'test1'
#在分支1中修改文件
mt@Mars:~/aaa$ echo "Test1" >> file
mt@Mars:~/aaa$ cat file
This is a file.
Test1
mt@Mars:~/aaa$ git status
# On branch test1
# Changes not staged for commit:
#   (use "git add ..." to update what will be committed)
#   (use "git checkout -- ..." to discard changes in working directory)
#
#    modified:   file
#
no changes added to commit (use "git add" and/or "git commit -a")
#切换到test2分支
mt@Mars:~/aaa$ git checkout test2
M    file
Switched to branch 'test2'
#此时发现file也是被修改的状态！！！！！照我的理解，分支之间，这种修改应该是不可见的。
mt@Mars:~/aaa$ git status
# On branch test2
# Changes not staged for commit:
#   (use "git add ..." to update what will be committed)
#   (use "git checkout -- ..." to discard changes in working directory)
#
#    modified:   file
#
no changes added to commit (use "git add" and/or "git commit -a")
#在test2分支中直接提交修改，就把在test1中做的修改给提交了。。FT。。
mt@Mars:~/aaa$ git commit -a
[test2 2b0b04f] test222
 Committer: mt
Your name and email address were configured automatically based
on your username and hostname. Please check that they are accurate.
You can suppress this message by setting them explicitly:

    git config --global user.name "Your Name"
    git config --global user.email [e-mail]

After doing this, you may fix the identity used for this commit with:

    git commit --amend --reset-author

 1 file changed, 1 insertion(+)
mt@Mars:~/aaa$ cat file
This is a file.
Test1
#再切回test1
mt@Mars:~/aaa$ git checkout test1
Switched to branch 'test1'
#发现此时test1中的文件反而是没有修改之前的内容
mt@Mars:~/aaa$ cat file
This is a file.
mt@Mars:~/aaa$ git status
# On branch test1
nothing to commit (working directory clean)
mt@Mars:~/aaa$
#在test1中再次修改
mt@Mars:~/aaa$ echo "NewTTT" >> file
#使用stash隐藏修改
mt@Mars:~/aaa$ git stash
Saved working directory and index state WIP on test1: 9ff6019 file modify
HEAD is now at 9ff6019 file modify
#切到test2分支，不会察觉到文件被修改过
mt@Mars:~/aaa$ git checkout test2
Switched to branch 'test2'
mt@Mars:~/aaa$ cat file
This is a file.
Test1
mt@Mars:~/aaa$ git checkout test1
Switched to branch 'test1'
#回到test1，用stash查看栈中的内容
mt@Mars:~/aaa$ git stash list
stash@{0}: WIP on test1: 9ff6019 file modify
mt@Mars:~/aaa$ cat file
This is a file.
#找回隐藏的修改
mt@Mars:~/aaa$ git stash apply stash@{0}
# On branch test1
# Changes not staged for commit:
#   (use "git add ..." to update what will be committed)
#   (use "git checkout -- ..." to discard changes in working directory)
#
#    modified:   file
#
no changes added to commit (use "git add" and/or "git commit -a")
#看，文件恢复到了之前修改的状态
mt@Mars:~/aaa$ cat file
This is a file.
NewTTT
mt@Mars:~/aaa$ git status
# On branch test1
# Changes not staged for commit:
#   (use "git add ..." to update what will be committed)
#   (use "git checkout -- ..." to discard changes in working directory)
#
#    modified:   file
#
no changes added to commit (use "git add" and/or "git commit -a")
#在test1中提交它
mt@Mars:~/aaa$ git commit -a
[test1 e6448ad] Newtt.
 Committer: mt
Your name and email address were configured automatically based
on your username and hostname. Please check that they are accurate.
You can suppress this message by setting them explicitly:

    git config --global user.name "Your Name"
    git config --global user.email [e-mail]

After doing this, you may fix the identity used for this commit with:

    git commit --amend --reset-author

 1 file changed, 1 insertion(+)
mt@Mars:~/aaa$ git status
# On branch test1
nothing to commit (working directory clean)
mt@Mars:~/aaa$ cat file
This is a file.
NewTTT
mt@Mars:~/aaa$ git checkout test2
Switched to branch 'test2'
mt@Mars:~/aaa$ cat file
This is a file.
Test1