Android 实现双击返回键退出App

public class MainActivity extends AppCompatActivity {

    private long lastClickTime = 0;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

    }

    @Override
    public void onBackPressed() {
//        super.onBackPressed();//一定要将改行删掉
        if (lastClickTime <= 0) {
            Toast.makeText(this, "再点击一下，退出应用", Toast.LENGTH_SHORT).show();
            lastClickTime = System.currentTimeMillis();
        } else {
            if ((System.currentTimeMillis() - lastClickTime) > 3000) {  //这里3000，表示两次点击的间隔时间
                Toast.makeText(this, "再点击一下，退出应用", Toast.LENGTH_SHORT).show();
                lastClickTime = System.currentTimeMillis();
            } else {
                System.exit(0);
            }

        }

    }
}