一…就….

The construction “一…就….”

“一…就….” ( “ as soon as …then….”) indicates that two motions or actions occur in quick succession. These two motions or actions can be performed by the same subject or by two different subjects. For example,

陈老师一进教师就开始上课。（same subject）
我一着急，就回答错了。（same subject）
北京一到五月，天气就热起来了。（two different subjects）
她一叫，我们就都出来了。（two different subjects）