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实验5 Java类库和常用类（一）

一. 实验目的及实验环境

1理解类库的概念，掌握分析、应用类库中的类的方法。

2熟练掌握Math类的常用方法。熟悉Random类的常用方法。 3理解String类的特性，熟练掌握String类的常用方法。 4能用Date类创建对象，熟练掌握Date类的常用方法。

5熟练掌握SimpleDateFormat解析日期和设置日期输出格式。 6学会查阅Java API在线参考文档和离线文档的方法。

二. 实验内容

1 基本内容（实验前请及时熟悉如下相关内容）

1）练习使用Math类的常用方法。 2）应用String类编程练习。

3）编写程序应用Random类生成随机数。 4）练习使用Date类的常用方法。

5）查阅Java API在线参考文档和下载Java API离线文档。

示例1. 应用SimpleDateFormat类的程序示例如下,共同学们模仿参考。

import java.text.*; import java.util.Date;

public class FormatDateTime {

public static void main(String[] args) {

SimpleDateFormat myFmt = new SimpleDateFormat(\年MM月dd日 HH时mm分ss秒\);

SimpleDateFormat myFmt1 = new SimpleDateFormat(\); SimpleDateFormat myFmt2 = new SimpleDateFormat(\HH:mm:ss\);// 等价于now.toLocaleString()

SimpleDateFormat myFmt3 = new SimpleDateFormat(\年MM月dd日 HH时mm分ss秒 E \);

SimpleDateFormat myFmt4 = new SimpleDateFormat(\一年中的第 D 天 一年中第w个星期 一月中第W个星期 在一天中k时 z时区\); Date now = new Date();//当前时间

System.out.println(myFmt.format(now)); System.out.println(myFmt1.format(now)); System.out.println(myFmt2.format(now)); System.out.println(myFmt3.format(now)); System.out.println(myFmt4.format(now));

System.out.println(now.toGMTString());//The method toGMTString() from the type Date is deprecated.

System.out.println(now.toLocaleString()); System.out.println(now.toString()); } }

示例2. 应用GregorianCalendar类的程序示例如下,共同学们模仿参考。

import java.util.GregorianCalendar; import java.util.Date;

import java.text.DateFormat;

//public class DateExample5 { public class TestGregorian {

public static void main(String[] args) { DateFormat dateFormat =

DateFormat.getDateInstance(DateFormat.FULL); // Create our Gregorian Calendar.

GregorianCalendar cal = new GregorianCalendar(); // Set the date and time of our calendar // to the system′s date and time cal.setTime(new Date());

System.out.println(\ + dateFormat.format(cal.getTime()));

// Set the day of week to FRIDAY

cal.set(GregorianCalendar.DAY_OF_WEEK, GregorianCalendar.FRIDAY); System.out.println(\ + dateFormat.format(cal.getTime())); int friday13Counter = 0;

while (friday13Counter <= 10) {

// Go to the next Friday by adding 7 days. cal.add(GregorianCalendar.DAY_OF_MONTH, 7); // If the day of month is 13 we have // another Friday the 13th.

if (cal.get(GregorianCalendar.DAY_OF_MONTH) == 13) { friday13Counter++;

System.out.println(dateFormat.format(cal.getTime())); } } } }

2 综合实验：

2.1 (Y. Daniel Liang 英文版第10版P360：*9.3 或英文版八版P296：8.3*) (Using the Date class) Write a program that creates a Date object, sets its elapsed time to 10000, 100000, 10000000, 10000000, 100000000, 1000000000, 10000000000, 100000000000, and displays the date and time using the toString() method, respectively.

2.2(Y. Daniel Liang 英文版第10版P360：*9.4 或英文版八版P296：8.4*) (Using the Random class) Write a program that creates a Random object with seed 1000 and displays the first 50 random integers between 0 and 100 using the nextInt(100) method.

2.3 (Y. Daniel Liang 英文版第10版P361：*9.5 或英文版八版P296：8.5*) (Using the GregorianCalendar class) Java API has the GregorianCalendar class in the java.util package that can be used to obtain the year, month, and day of a date. The no-arg constructor constructs an instance for the current date, and the methods get(GregorianCalendar.YEAR), get(GregorianCalendar.MONTH), and

get(GregorianCalendar.DAY_OF_MONTH) return the year, month, and day. Write a program to perform two tasks:

■ Display the current year, month, and day.

■ The GregorianCalendar class has the setTimeInMillis(long), which can be used to set a specified elapsed time since January 1, 1970. Set the value to 1234567898765L and display the year, month, and day.

2.4(Y. Daniel Liang英文版第10版P284：**7.34 或英文版八版P337：9.11**) (Sorting characters in a string) Write a method that returns a sorted string using the following header:

public static String sort(String s)

For example, sort(\

Write a test program that prompts the user to enter a string and displays the sorted string.

2.5 (Y. Daniel Liang英文版八版P201：*5.50) (Count uppercase letters) Write a program that prompts the user to enter a string and displays the number of the uppercase letters in the string.

或

(Y. Daniel Liang英文版八版P338：9.15*) (Finding the number of uppercase letters in a string) Write a program that passes a string to the main method and displays the number of uppercase letters in a string.

2.6附加题（供学有余力同学选做，平时成绩有加分！）

(Y. Daniel Liang英文版第10版P238：**6.18 或英文版八版P336：9.3**) (Checking password) Some Websites impose certain rules for passwords. Write a method that checks whether a string is a valid password. Suppose the password rule is as follows: ■ A password must have at least eight characters. ■ A password consists of only letters and digits. ■ A password must contain at least two digits.