関連ワード:  why we need abstract class in java    why we need abstract class in java 8    why we use abstract class in java instead of interface    why we use abstract class in java with example    why we need constructor in abstract class in java    why do we use abstract class in java    why we use abstract class and interface in java    why we use interface over abstract class in java    why we create abstract class in java    why do we need interface when we have abstract class in java