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算法(第4版)
知识点
- Transaction类的设计
- Date类的纠错
题目
1.2.13 用我们对Date的实现作为模板实现Transaction类型
1.2.13 Using our implementation of Date as a model(page91),develop an implementation of Transaction.
题目
1.2.14 用我们对Date的实现作为模板实现Transaction的euqal()函数
1.2.14 Using our implementation of equals() in Date as a model(page103),develop implementations of equals() for Transaction.
分析
本人所有简书的算法文章详细分析已经移入小专栏：算法四习题详解，欢迎大家订阅
答案
public class Transaction {
private Date when;
private String who;
private double amount;
public Date when(){
return this.when;
}
public double amount(){
return this.amount;
}
public String who(){
return this.who;
}
public Transaction(String who,Date when,double amount){
this.who = who;
this.when = when;
this.amount = amount;
}
public String toString(){
return "" + this.who + " at " + this.when + " transaction " + this.amount;
}
public boolean equals(Object x){
if (this == x)return true;
if (x == null) return false;
if(this.getClass()!=x.getClass()) return false;
Transaction that = (Transaction) x;
if (!this.when.equals(that.when)) return false;
if (!this.who.equals(that.who)) return false;
if (this.amount != that.amount) return false;
return true;
}
public static void main(String[] args) throws Exception {
// TODO Auto-generated method stub
Date date=new Date(1996,12,5);
Transaction tran=new Transaction("Kyson",date,1000);
StdOut.println(tran.toString());
}
}
其中对于Date类有纠错部分如下
public class Date {
@SuppressWarnings("unused")
private final int year;
@SuppressWarnings("unused")
private final int month;
@SuppressWarnings("unused")
private final int day;
/**
* 纠错一：这里原来是写死的，现在不写死了，因为yearFirstTwo的意思是获取年份的前两位，在构造函数中再指定
*/
private final int yearFirstTwo;
private static final int DAYPERWEEK = 7;
public Date(int year, int month, int day) throws Exception {
if (year < 0 || month < 0 || day < 0) {
Exception exception = new Exception("年月日要大于0");
throw exception;
}
if (month > 12) {
Exception exception = new Exception("年份要小于等于12");
throw exception;
}
switch (month) {
case 3:
case 5:
case 7:
case 8:
case 10:
case 12:
case 1: {
if (day > 31) {
Exception exception = new Exception(month + "月小于31号");
throw exception;
}
}
break;
case 2: {
if (day > 29) {
Exception exception = new Exception(month + "月小于等于29号");
throw exception;
}
boolean leapYear = this.isLeapYear(year);
if (!leapYear) {
if (day > 28) {
Exception exception = new Exception(month + "月小于等于28号");
throw exception;
}
}
}
break;
case 4:
case 6:
case 9:
case 11: {
if (day > 30) {
Exception exception = new Exception(month + "月小于30号");
throw exception;
}
}
break;
default:
break;
}
this.day = day;
this.year = year;
this.month = month;
yearFirstTwo = year / 100;
}
/**
* 纠错二：判断闰年的方法单独写出来，以前只是单纯的取余4，现在单独写一个方法
*/
/**
* 判断是否为闰年
* 判断闰年的方法：闰年满足两个条件（满足一个即为闰年）
* 1、能被4整除但不能被100整除
* 2、能被400整除
* @param year
* @return
*/
private boolean isLeapYear(int year)
{
if(year%100!=0&&year%4==0)
return true;
else if(year%100==0&&year%400==0)
return true;
else
return false;
}
public String dayOfTheWeek(){
String resultWeek = "";
int tempMonth = this.month;
int tempYear = this.year;
int tempDay = this.day;
if (this.month == 1 || this.month == 2) {
tempMonth += 12;
tempYear --;
}
int y = tempYear - yearFirstTwo * 100;
int floor1 = (int) Math.floor(y/4);
int floor2 = (int) (yearFirstTwo / 4);
int floor3 = (int) Math.floor(26 * (tempMonth+1)/10);
int w = y + floor1 + floor2 -2 * yearFirstTwo + floor3 + tempDay - 1;
int key = w % DAYPERWEEK;
if (key <0) {
key = key + 7;
}
switch (key) {
case 0:
resultWeek = "星期日";
break;
case 1:
resultWeek = "星期一";
break;
case 2:
resultWeek = "星期二";
break;
case 3:
resultWeek = "星期三";
break;
case 4:
resultWeek = "星期四";
break;
case 5:
resultWeek = "星期五";
break;
case 6:
resultWeek = "星期六";
break;
default:
break;
}
return resultWeek;
}
public String toString(){
return ""+ month + "/" + day + "/" + year;
}
public boolean equals(Object that){
if (this == that) {
return true;
}
if (that == null) {
return false;
}
Date xDate = (Date)that;
if (this.year != xDate.year) return false;
if (this.month != xDate.month) return false;
if (this.day != xDate.day) return false;
return true;
}
public static void main(String[] args) throws Exception {
// TODO Auto-generated method stub
Date date = new Date(1996, 12, 5);
String week = date.dayOfTheWeek();
System.out.println( date + " is :" + week);
}
}
纠错一：这里原来是写死的，现在不写死了，因为yearFirstTwo的意思是获取年份的前两位，在构造函数中再指定
纠错二：判断闰年的方法单独写出来，以前只是单纯的取余4，现在单独写一个方法
代码索引
视频讲解
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