Can't get plugin to work

I'm trying to make a super simple plugin that replaces cobblestone with stone when it's placed. I looked at some tutorials and I can't get the most bare bone thing to work.

Code:

package aqua.nocobble;

import org.bukkit.plugin.java.JavaPlugin;

class NoCobble extends JavaPlugin {

    public void onEnable(){
        System.out.println("NoCobble Enabled.");
    }

    public void onDisable(){
        System.out.println("NoCobble Disabled.");
    }
}

Gives me this error:

Code:

[SEVERE] Could not load 'plugins/NoCobble.jar' in folder 'plugins':
java.lang.NoSuchMethodException: aqua.nocobble.NoCobble.<init>()
        at java.lang.Class.getConstructor0(Class.java:2723)
        at java.lang.Class.getConstructor(Class.java:1674)
        at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.j                                                                                        ava:137)
        at org.bukkit.plugin.SimplePluginManager.loadPlugin(SimplePluginManager.                                                                                        java:160)
        at org.bukkit.plugin.SimplePluginManager.loadPlugins(SimplePluginManager                                                                                        .java:108)
        at org.bukkit.craftbukkit.CraftServer.loadPlugins(CraftServer.java:85)
        at net.minecraft.server.MinecraftServer.e(MinecraftServer.java:217)
        at net.minecraft.server.MinecraftServer.a(MinecraftServer.java:204)
        at net.minecraft.server.MinecraftServer.init(MinecraftServer.java:144)
        at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:259)
        at net.minecraft.server.ThreadServerApplication.run(SourceFile:394)

 

Your plugin.yml is incorrent, plugin path should be
aqua.nocobble.NoCobble.NoCobble