public class MyApplication extends Application {
   
   public String appVersion = "v1.0";
   
   //当前登录用户
   private User loginUser = new User();
   
   public User getLoginUser(){
   return loginUser;
   }
   
   public void userLogin(User user){
   loginUser.setUserId(user.getUserId());
   loginUser.setUserName(user.getUserName());
   }
   
   public void userLogout(){
   loginUser = new User();
   }
}
　　

public class MainActivity extends Activity {
 
 private MyApplication mApplication;
 
 @Override
 protected void onCreate(Bundle savedInstanceState) {
   super.onCreate(savedInstanceState);
   setContentView(R.layout.activity_main);
   // 获取整个应用的Application对象
   // 在不同的Activity中获取的对象是同一个
   mApplication = (MyApplication) getApplication();
 }
 
 /**
 * 一般只有在登录界面中设置登录用户信息，在其他的Activity中
 * 只要通过Application对象就可以获取登录用户信息
 */
 private void login(){
   User user = new User();
   user.setUserId(1);
   user.setUserName("Raysmond");
   // 将登录用户信息保存到Application对象中
   mApplication.userLogin(user);
 }
}