为什么使用ActivityManager就会报错误

为什么使用ActivityManager就会报异常
初学者，这个问题纠结一天了。。。

为什么我的代码里有这句就会报异常，注释掉以后就好了。

Java code

ActivityManager am = (ActivityManager)getSystemService(Context.ACTIVITY_SERVICE) ;

04-08 12:05:26.430: D/AndroidRuntime(324): Shutting down VM
04-08 12:05:26.440: W/dalvikvm(324): threadid=1: thread exiting with uncaught exception (group=0x4001d800)
04-08 12:05:26.450: E/AndroidRuntime(324): FATAL EXCEPTION: main
04-08 12:05:26.450: E/AndroidRuntime(324): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{zzx.Android/zzx.Android.Test}: java.lang.IllegalStateException: System services not available to Activities before onCreate()
04-08 12:05:26.450: E/AndroidRuntime(324): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2585)
04-08 12:05:26.450: E/AndroidRuntime(324): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
04-08 12:05:26.450: E/AndroidRuntime(324): at android.app.ActivityThread.access$2300(ActivityThread.java:125)
04-08 12:05:26.450: E/AndroidRuntime(324): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
04-08 12:05:26.450: E/AndroidRuntime(324): at android.os.Handler.dispatchMessage(Handler.java:99)
04-08 12:05:26.450: E/AndroidRuntime(324): at android.os.Looper.loop(Looper.java:123)
04-08 12:05:26.450: E/AndroidRuntime(324): at android.app.ActivityThread.main(ActivityThread.java:4627)
04-08 12:05:26.450: E/AndroidRuntime(324): at java.lang.reflect.Method.invokeNative(Native Method)
04-08 12:05:26.450: E/AndroidRuntime(324): at java.lang.reflect.Method.invoke(Method.java:521)
04-08 12:05:26.450: E/AndroidRuntime(324): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
04-08 12:05:26.450: E/AndroidRuntime(324): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
04-08 12:05:26.450: E/AndroidRuntime(324): at dalvik.system.NativeStart.main(Native Method)
04-08 12:05:26.450: E/AndroidRuntime(324): Caused by: java.lang.IllegalStateException: System services not available to Activities before onCreate()
04-08 12:05:26.450: E/AndroidRuntime(324): at android.app.Activity.getSystemService(Activity.java:3526)
04-08 12:05:26.450: E/AndroidRuntime(324): at zzx.Android.Test.<init>(Test.java:37)
04-08 12:05:26.450: E/AndroidRuntime(324): at java.lang.Class.newInstanceImpl(Native Method)
04-08 12:05:26.450: E/AndroidRuntime(324): at java.lang.Class.newInstance(Class.java:1429)
04-08 12:05:26.450: E/AndroidRuntime(324): at android.app.Instrumentation.newActivity(Instrumentation.java:1021)
04-08 12:05:26.450: E/AndroidRuntime(324): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2577)
04-08 12:05:26.450: E/AndroidRuntime(324): ... 11 more

[解决办法]
IllegalStateException: System services not available to Activities before onCreate()
根据报错，你这段代码放的位置不对，在程序create前是不允许调用的

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