public interface SingletonBeanRegistry {    /**     * Register the given existing object as singleton in the bean registry,     * under the given bean name.     * <p>The given instance is supposed to be fully initialized; the registry     * will not perform any initialization callbacks (in particular, it won‘t     * call InitializingBean‘s {@code afterPropertiesSet} method).     * The given instance will not receive any destruction callbacks     * (like DisposableBean‘s {@code destroy} method) either.     * <p>When running within a full BeanFactory: <b>Register a bean definition     * instead of an existing instance if your bean is supposed to receive     * initialization and/or destruction callbacks.</b>     * <p>Typically invoked during registry configuration, but can also be used     * for runtime registration of singletons. As a consequence, a registry     * implementation should synchronize singleton access; it will have to do     * this anyway if it supports a BeanFactory‘s lazy initialization of singletons.     * @param beanName the name of the bean     * @param singletonObject the existing singleton object     * @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet     * @see org.springframework.beans.factory.DisposableBean#destroy     * @see org.springframework.beans.factory.support.BeanDefinitionRegistry#registerBeanDefinition     */    void registerSingleton(String beanName, Object singletonObject);    /**     * Return the (raw) singleton object registered under the given name.     * <p>Only checks already instantiated singletons; does not return an Object     * for singleton bean definitions which have not been instantiated yet.     * <p>The main purpose of this method is to access manually registered singletons     * (see {@link #registerSingleton}). Can also be used to access a singleton     * defined by a bean definition that already been created, in a raw fashion.     * <p><b>NOTE:</b> This lookup method is not aware of FactoryBean prefixes or aliases.     * You need to resolve the canonical bean name first before obtaining the singleton instance.     * @param beanName the name of the bean to look for     * @return the registered singleton object, or {@code null} if none found     * @see ConfigurableListableBeanFactory#getBeanDefinition     */    Object getSingleton(String beanName);    /**     * Check if this registry contains a singleton instance with the given name.     * <p>Only checks already instantiated singletons; does not return {@code true}     * for singleton bean definitions which have not been instantiated yet.     * <p>The main purpose of this method is to check manually registered singletons     * (see {@link #registerSingleton}). Can also be used to check whether a     * singleton defined by a bean definition has already been created.     * <p>To check whether a bean factory contains a bean definition with a given name,     * use ListableBeanFactory‘s {@code containsBeanDefinition}. Calling both     * {@code containsBeanDefinition} and {@code containsSingleton} answers     * whether a specific bean factory contains a local bean instance with the given name.     * <p>Use BeanFactory‘s {@code containsBean} for general checks whether the     * factory knows about a bean with a given name (whether manually registered singleton     * instance or created by bean definition), also checking ancestor factories.     * <p><b>NOTE:</b> This lookup method is not aware of FactoryBean prefixes or aliases.     * You need to resolve the canonical bean name first before checking the singleton status.     * @param beanName the name of the bean to look for     * @return if this bean factory contains a singleton instance with the given name     * @see #registerSingleton     * @see org.springframework.beans.factory.ListableBeanFactory#containsBeanDefinition     * @see org.springframework.beans.factory.BeanFactory#containsBean     */    boolean containsSingleton(String beanName);    /**     * Return the names of singleton beans registered in this registry.     * <p>Only checks already instantiated singletons; does not return names     * for singleton bean definitions which have not been instantiated yet.     * <p>The main purpose of this method is to check manually registered singletons     * (see {@link #registerSingleton}). Can also be used to check which singletons     * defined by a bean definition have already been created.     * @return the list of names as a String array (never {@code null})     * @see #registerSingleton     * @see org.springframework.beans.factory.support.BeanDefinitionRegistry#getBeanDefinitionNames     * @see org.springframework.beans.factory.ListableBeanFactory#getBeanDefinitionNames     */    String[] getSingletonNames();    /**     * Return the number of singleton beans registered in this registry.     * <p>Only checks already instantiated singletons; does not count     * singleton bean definitions which have not been instantiated yet.     * <p>The main purpose of this method is to check manually registered singletons     * (see {@link #registerSingleton}). Can also be used to count the number of     * singletons defined by a bean definition that have already been created.     * @return the number of singleton beans     * @see #registerSingleton     * @see org.springframework.beans.factory.support.BeanDefinitionRegistry#getBeanDefinitionCount     * @see org.springframework.beans.factory.ListableBeanFactory#getBeanDefinitionCount     */    int getSingletonCount();}