再点一次退出最简单逻辑

<pre name="code" class="java">private int firstTime=0;public void onBackPressed() {          if ((System.currentTimeMillis() - firstTime) > 2000) {              Toast.makeText(MainActivity.this,"再点一次退出",0).show();              firstTime = System.currentTimeMillis();          } else {              finish();          }      }