startActivityForResult(Intent intent, Int requestCode)
setResut(int resultCode, Intent intent)
onActivityResult(int requestCode, int resultCode, Intent intent)

Intent intent=new Intent();
intent.setClass(A.this, B.class);
Bundle bundle=new Bundle();
String str1="aaaaaa";
bundle.putString("str1", str1);
intent.putExtras(bundle);
startActivityForResult(intent, 0);//这里采用startActivityForResult来做跳转，此处的0为一个依据，可以写其他的值，但一定要>=0

protected void onActivityResult(int requestCode, int resultCode, Intent data) {
switch (resultCode) { //resultCode为回传的标记，我在B中回传的是RESULT_OK
  case RESULT_OK:
  Bundle b=data.getExtras(); //data为B中回传的Intent
  String str=b.getString("str1");//str即为回传的值
  break;
default:
  break;
  }
}

setResult(RESULT_OK, intent); //intent为A传来的带有Bundle的intent，当然也可以自己定义新的Bundle
finish();//此处一定要调用finish()方法

public final void setResult(int resultCode, Intent data) {
    synchronized (this) {
      mResultCode = resultCode;
      mResultData = data;
    }
  }

  public void finish() {
    if (mParent == null) {
      int resultCode;
      Intent resultData;
      synchronized (this) {
        resultCode = mResultCode;
        resultData = mResultData;
      }
      if (Config.LOGV) Log.v(TAG, "Finishing self: token=" + mToken);
      try {
        if (ActivityManagerNative.getDefault()
          .finishActivity(mToken, resultCode, resultData)) {
          mFinished = true;
        }
      } catch (RemoteException e) {
        // Empty
      }
    } else {
      mParent.finishFromChild(this);
    }
  }

@Override
  public void onBackPressed() {
    Log.i(TAG, "onBackPressed");
    setResult(Const.LIVE_OK);
    super.onBackPressed();
  }