# Overview

1. 需要先定义一个.proto文件
2. 运行protoc命令，如protoc -I=$SRC_DIR --java_out=$DST_DIR \$SRC_DIR/addressbook.proto
3. 之后使用指定目录的.java文件

# 结论

• tag number最重要
• if tag number not change, but field name change, then output would using the new field name

For more described in tutorials,

• you must not change the tag numbers of any existing fields.
• you may delete optional or repeated fields.
• you may add new optional or repeated fields but you must use fresh tag numbers (i.e. tag numbers that were never used in this protocol buffer, not even by deleted fields).