public static void showBar() { 
  try { 
     Process proc = Runtime.getRuntime().exec( 
       new String[] { "am", "startservice", "-n", 
         "com.android.systemui/.SystemUIService" }); 
     proc.waitFor(); 
   } catch (Exception e) { 
     e.printStackTrace(); 
   } 
 } 
 public static void closeBar(Context context) { 
   try { 
    // 需要root 权限 
     Build.VERSION_CODES vc = new Build.VERSION_CODES(); 
     Build.VERSION vr = new Build.VERSION(); 
     String ProcID = "79"; 
if (vr.SDK_INT >= vc.ICE_CREAM_SANDWICH) { 
       ProcID = "42"; // ICS AND NEWER 
    } 
   // 需要root 权限 
    Process proc = Runtime.getRuntime().exec( 
 new String[] { 
        "su", 
        "-c", 
        "service call activity " + ProcID 
          + " s16 com.android.systemui" }); // WAS 79 
    proc.waitFor(); 
   } catch (Exception ex) { 
     Toast.makeText(context, ex.getMessage(), Toast.LENGTH_LONG).show(); 
   } 
}

<activity android:name="Demo"
   android:label="@string/app_name"
   android:theme="@android:style/Theme.NoTitleBar.Fullscreen" >
 <intent-filter>
  <action android:name="android.intent.action.MAIN" />
  <category android:name="android.intent.category.LAUNCHER" />
 </intent-filter>
</activity>

getWindow().getDecorView().setSystemUiVisibility
 (View.SYSTEM_UI_FLAG_LOW_PROFILE); 

getWindow().getDecorView().setSystemUiVisibility
 (View.SYSTEM_UI_FLAG_HIDE_NAVIGATION);

# kill com.android.systemui
# service call activity 79 s16 com.android.systemui

Process proc = Runtime.getRuntime().exec(new String[]{"su","-c","service
 call activity 79 s16 com.android.systemui"});
proc.waitFor();
Process proc = Runtime.getRuntime().exec(new String[]{"am","startservice","-n","com.android.systemui/.SystemUIService"});
proc.waitFor();