関連ワード:  why do we need interface in java    why do we use interface in java    why do we use interface in java with example    why do we need functional interface in java    why do we need marker interface in java    why do we need functional interface in java 8    why do we need serializable interface in java    why do we use functional interface in java    why do we use runnable interface in java    why do we need static methods in interface java 8