public abstract class Date5 { public abstract boolean isValid(int year,int month,int day); public abstract Date5 daysAfter(int days); public abstract int between(Date5 d2); } 声明一个类,继承Date5,并实现其中的方法
public class test extends Date5{ public boolean isValid(int year,int month,int day){} public Date5 daysAfter(int days){} public int between(Date5 d2){} }