如何使用sed命令批量更改java包声明?

Previously, my java package declarations all start with 'zn' like "package zn.tree". Now after I changed the java folder path to remove 'zn' folder, I also want to change all java declarations to remove the prefix 'zn.' in a batch way. For example, I want change "package zn.tree" to "package tree". Previously, my java package declarations all st