関連ワード:  why do we need java interface    why do we use java interfaces    why do we need static methods in interface java 8    why do we need functional interface in java    why do we need marker interface in java    why do we need default method in java 8 interfaces    why do we need functional interface in java 8    why do we need serializable interface in java    why do we need interface and abstract class in java    purpose of java interfaces