我已经下载了jdk 1.8.0_131
当我打开命令提示符并编写以下命令时 - java -version它给我输出
java version "1.8.0_131"
Java(TM) SE Runtime Environment (build 1.8.0_131-b11)
Java HotSpot(TM) 64-Bit Server VM (build 25.131-b11, mixed mode)
但是当我编写以下命令时：javac -version它给我输出
'javac' is not recognized as an internal or external command,
operable program or batch file.
我已将系统变量路径编辑为 - C：\ Progra~1 \ Java \ jdk1.8.0_131 \ bin;
当我执行以下命令时：“C：\ Program Files \ Java \ jdk1.8.0_131 \ bin \ javac”-version
它给了我输出：
javac 1.8.0_131
所以我知道我已经安装了正确的java版本
我还检查了上面的文件夹，并在那里找到了一个javac.exe。请帮忙。
编辑：
我终于解决了这个问题。我正在做的是编辑“Path”变量，当我不得不做一个名为“PATH”的新变量和以下细节时：
Variable name : PATH
Variable value : c:\Program Files\Java\jdk1.8.0_xx\bin;[Existing Entries...
答案 0 :(得分：1)
您是否尝试重新启动“cmd.exe”，因为将bin目录添加到PATH？
如果您确认您的PATH包含了java bin目录，并且您可以在该位置看到“javac.exe”二进制文件，那么所有这些都应该正确设置。
答案 1 :(得分：0)
在Windows中，您需要将require "db"
require "sqlite3"
module Project
Migrations = [] of Migration
class Migration
def initialize(@version : Int)
end
# Registers a callback that will be called when the `up`-method is called.
# The callback must return either `true` for a successful migration,
# or `false` for a failed migration. If an `up` migration has
# failed, the `down` migration will be called to restore the database
# back to its previous state.
# The callback will receive an instance of `DB::Database`
#
# Example:
#
# ```
# migration = Migration.new(1)
#
# migration.register_up |db| do
# # Advance migration
# end
#
# migration.register_down |db| do
# # Recede migration
# end
# ```
def register_up(&block : (DB::Database) -> Bool)
@up = block
end
# Registers a callback that will be called when the `down`-method is called.
# See the `register_up` method for more information
def register_down(&block : (DB::Database) -> Bool)
@down = block
end
# Advances DB to the next version
def up(conn : DB::Database)
result = @up.call(conn)
unless result
# Failed migration, rollback
@down.call(conn)
raise Exception.new(`Failed to migrate database to version: #{@version}. Rolling back.`)
end
end
# Recedes DB to the previous version
def down(conn : DB::Database)
result = @down.call(conn)
unless result
# Failed migration, rollback
@up.call(conn)
raise Exception.new(`Failed to migrate database to version: #{@version - 1}. Rolling back.`)
end
end
end
end
的路径添加到jdk_your_version/bin变量。将此行添加到PATH：
PATH保存。然后重新启动C:\Progra~1\Java\jdk1.8.0_131\bin;
，因为它不会自动更新open cmd的路径。然后您应该能够看到CMD正在运行：
javac