Intent intent= new Intent(Intent.ACTION_MAIN); 
intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK); //如果是服务里调用，必须加入new task标识 
intent.addCategory(Intent.CATEGORY_HOME); 
startActivity(intent); 

Intent intent = new Intent(Intent.ACTION_MAIN,null); 
ntent.addCategory(Intent.CATEGORY_HOME); 
startActivity(intent); 

AudioManager mAudioManager = (AudioManager) getSystemService(Context.AUDIO_SERVICE); 
mAudioManager.adjustStreamVolume(AudioManager.STREAM_MUSIC, AudioManager.ADJUST_LOWER, 
    AudioManager.FX_FOCUS_NAVIGATION_UP); 
mAudioManager.adjustStreamVolume(AudioManager.STREAM_MUSIC, AudioManager.ADJUST_LOWER, 
    AudioManager.FX_FOCUS_NAVIGATION_UP);