Case 1: data sorting in string
Requirement: there is a string: "91 27 46 38 50". Please write a program to realize it. The final output result is: "27 38 46 50 91"
Idea: 1. Define a string
2. Store the numeric data in the string into an array of int type
Get each numeric data in the string?
public String[] split(String regex)
Define an int array and store each element in the String [] array in the int array
public static int parseInt(String s)
3. Sort int array
4. Splice the elements in the sorted int array to get a string. Here, the splicing is implemented by StringBuilder
5. Output results
package test;
import java.util.Arrays;
public class Test48 {
public static void main(String[] args) {
// 1. Define a string
String s = "91 27 46 38 50";
// 2. Store the numeric data in the string into an array of int type
// Get each numeric data in the string?
// public String[] split(String regex)
// Define an int array and store each element in the String [] array in the int array
// public static int parseInt(String s)
String[] strArray = s.split(" ");
int[] arr = new int[strArray.length];
for (int i = 0; i<strArray.length; i++){
arr[i] = Integer.parseInt(strArray[i]);
}
// 3. Sort int array
Arrays.sort(arr);
// 4. Splice the elements in the sorted int array to get a string. Here, the splicing is implemented by StringBuilder
StringBuilder sb = new StringBuilder();
for (int i = 0; i<arr.length; i++){
if (i == arr.length-1){
sb.append(arr[i]);
}else{
sb.append(arr[i]).append(" ");
}
}
String result = sb.toString();
// 5. Output results
System.out.println("The result of sorting is:"+result);
}
}Case 2: Date tools
Requirement: define a date tool class (DeteUtils), which contains two methods: convert the date to a string in the specified format; Parse the string into a date in the specified format, and then define a test class (DateDemo) to test the methods of the date tool class
Idea: 1. Define date tool class (DateUtils)
2. Define a dateToString method to convert the date into a string in the specified format
Return value type: String
Parameters: date, date, String format
3. Define a method stringToDate, which is used to parse the string into a date in the specified format
Return value type: Date
Parameters: String s, String format
4. Define the test class DateDemo and call the methods in the date tool class
Date utility class (DateUtils)
package test.test49;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
/**
* 1.Define date tool class (DateUtils)
* Tool class construction methods are private and member methods are static
*/
public class DateUtils {
private DateUtils(){
}
/**
* 2.Define a dateToString method to convert the date into a string in the specified format
* Return value type: String
* Parameters: date, date, String format
*/
public static String dateToString(Date date,String format){
SimpleDateFormat sdf = new SimpleDateFormat(format);
String s = sdf.format(date);
return s;
}
/**
* 3.Define a method stringToDate, which is used to parse the string into a date in the specified format
* Return value type: Date
* Parameters: String s, String format
*/
public static Date stringToDate(String s,String format) throws ParseException {
SimpleDateFormat sdf = new SimpleDateFormat(format);
Date d = sdf.parse(s);
return d;
}
}Test class (DateDemo)
package test.test49;
import java.text.ParseException;
import java.util.Date;
// 4. Define the test class DateDemo and call the methods in the date tool class
public class DateDemo {
public static void main(String[] args) throws ParseException {
// Create date object
Date d = new Date();
String s1 = DateUtils.dateToString(d, "yyyy year MM month dd day HH:mm:ss");
System.out.println(s1);
String s2 = DateUtils.dateToString(d, "yyyy year MM month dd day");
System.out.println(s2);
String s3 = DateUtils.dateToString(d, "HH:mm:ss");
System.out.println(s3);
System.out.println("--------");
String s = "2021-11-09 15:05:15";
Date date = DateUtils.stringToDate(s, "yyyy-MM-dd HH:mm:ss");
System.out.println(date);
}
}Case 3: February day
Demand: get the number of days in February of any year
Idea: 1. Enter any year on the keyboard
2. Set year, month and day of calendar object
Year: from keyboard entry
Month: set to March, and the month starts from 0, so the set value is 2
Day: set to January
3. March 1 is pushed forward one day, which is the last day of February
4. Just get the output of this day
package test;
import java.util.Calendar;
import java.util.Scanner;
public class Test50 {
public static void main(String[] args) {
// 1. Enter any year on the keyboard
Scanner sc = new Scanner(System.in);
System.out.println("Please enter the year:");
int year = sc.nextInt();
// 2. Set year, month and day of calendar object
// Year: from keyboard entry
// Month: set to March, and the month starts from 0, so the set value is 2
// Day: set to January
Calendar c = Calendar.getInstance();
c.set(year,2,1);
// 3. March 1 is pushed forward one day, which is the last day of February
c.add(Calendar.DATE,-1);
// 4. Just get the output of this day
int date = c.get(Calendar.DATE);
System.out.println(year+"In February"+date+"day");
}
}