エラーの意味が分かりません

前提・実現したいこと

eclipseを使ってアプリ開発をしています。
エミュレーター(？)で実行しようとしたら、unfortunately ～ stopped と出てきて実行できません

発生している問題・エラーメッセージ

Logのところに出ていたエラーです。

FATAL EXCEPTION: main
Process: com.example.memoapp, PID: 1765
ava.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.memoapp/com.example.memoapp.MainActivity}:
java.lang.ClassNotFoundException: Didn't find class"com.example.memoapp.MainActivity" on path: DexPathList[[zip file "/data/app/com.example.memoapp-2/base.apk"],nativeLibraryDirectories=[/vendor/lib, /system/lib]]
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2209)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access$800(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
Caused by: java.lang.ClassNotFoundException: Didn't find class"com.example.memoapp.MainActivity" on path: DexPathList[[zip file "/data/app/com.example.memoapp-2/base.apk"],nativeLibraryDirectories=[/vendor/lib, /system/lib]]
at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:56)
at java.lang.ClassLoader.loadClass(ClassLoader.java:511)
at java.lang.ClassLoader.loadClass(ClassLoader.java:469)
at android.app.Instrumentation.newActivity(Instrumentation.java:1065)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2199)
... 10 more
Suppressed: java.lang.ClassNotFoundException: com.example.memoapp.MainActivity
at java.lang.Class.classForName(Native Method)
at java.lang.BootClassLoader.findClass(ClassLoader.java:781)
at java.lang.BootClassLoader.loadClass(ClassLoader.java:841)
at java.lang.ClassLoader.loadClass(ClassLoader.java:504)
... 13
Caused by: java.lang.NoClassDefFoundError: Class not found using the boot
class loader; no stack available