用@Configuration注解該類，等價 與XML中配置beans；用@Bean標注方法等價于XML中配置bean。

@Configuration  
public class SpringConfig {  
  
    @Bean  
    public Piano piano(){  
        return new Piano();  
    }  
    @Bean(name = "counter")   
    public Counter counter(){  
        return  new Counter(12,"Shake it Off",piano());  
    }  
}