Java中的接口可以多继承

接口是常量值和方法定义的集合。接口是一种特殊的抽象类。

java类是单继承的。classB Extends classA

java接口可以多继承。Interface3 Extends Interface0, Interface1, interface……

以下是spring ApplicationContext 接口的代码，同时继承了多个接口

public interface ApplicationContext extends EnvironmentCapable, ListableBeanFactory, HierarchicalBeanFactory,
        MessageSource, ApplicationEventPublisher, ResourcePatternResolver { 
    /**
     * Return the unique id of this application context.
     * @return the unique id of the context, or {@code null} if none
     */
    String getId(); 
    /**
     * Return a name for the deployed application that this context belongs to.
     * @return a name for the deployed application, or the empty String by default
     */
    String getApplicationName(); 
    /**
     * Return a friendly name for this context.
     * @return a display name for this context (never {@code null})
     */
    String getDisplayName(); 
    /**
     * Return the timestamp when this context was first loaded.
     * @return the timestamp (ms) when this context was first loaded
     */
    long getStartupDate(); 
    /**
     * Return the parent context, or {@code null} if there is no parent
     * and this is the root of the context hierarchy.
     * @return the parent context, or {@code null} if there is no parent
     */
    ApplicationContext getParent(); 
    /**
     * Expose AutowireCapableBeanFactory functionality for this context.
     * <p>This is not typically used by application code, except for the purpose of
     * initializing bean instances that live outside of the application context,
     * applying the Spring bean lifecycle (fully or partly) to them.
     * <p>Alternatively, the internal BeanFactory exposed by the
     * {@link ConfigurableApplicationContext} interface offers access to the
     * {@link AutowireCapableBeanFactory} interface too. The present method mainly
     * serves as a convenient, specific facility on the ApplicationContext interface.
     * <p><b>NOTE: As of 4.2, this method will consistently throw IllegalStateException
     * after the application context has been closed.</b> In current Spring Framework
     * versions, only refreshable application contexts behave that way; as of 4.2,
     * all application context implementations will be required to comply.
     * @return the AutowireCapableBeanFactory for this context
     * @throws IllegalStateException if the context does not support the
     * {@link AutowireCapableBeanFactory} interface, or does not hold an
     * autowire-capable bean factory yet (e.g. if {@code refresh()} has
     * never been called), or if the context has been closed already
     * @see ConfigurableApplicationContext#refresh()
     * @see ConfigurableApplicationContext#getBeanFactory()
     */
    AutowireCapableBeanFactory getAutowireCapableBeanFactory() throws IllegalStateException; 
}

不允许类多重继承的主要原因是，如果A同时继承B和C，而B和C同时有一个D方法，A如何决定该继承那一个呢?

但接口不存在这样的问题，接口全都是抽象方法继承谁都无所谓，所以接口可以继承多个接口。

注意：

1.一个类如果实现了一个接口，则要实现该接口的所有方法。

2.方法的名字、返回类型、参数必须与接口中完全一致。如果方法的返回类型不是void，则方法体必须至少有一条return语句。

3.因为接口的方法默认是public类型的，所以在实现的时候一定要用public来修饰(否则默认为protected类型，缩小了方法的使用范围)。

以上就是极悦小编介绍的"Java中的接口可以多继承"，希望对大家有帮助，如有疑问，请在线咨询，有专业老师随时为您服务。