Java第二次实验

1. 本章学习总结
本章学习了Java多方面知识：控制台输入推荐用Scanner.nextLine()避免问题，还涉及 IDE 操作与 String.split；身份证排序用Arrays.sort和String.subString，结构化编程且注意输入方法；需了解 StringBuilder 优于+拼接字符串；动态数组第一维预定义、第二维动态定；ArrayList有add等方法，可替代数组，可查JDK文档深入学习。
2. 书面作业
2.1 综合小测验

2.2 身份证排序

点击查看代码

import java.util.*;public class Main {public static void main(String[] args) {Scanner scanner = new Scanner(System.in);int n = Integer.parseInt(scanner.nextLine());List<String> idCards = new ArrayList<>();for (int i = 0; i < n; i++) {idCards.add(scanner.nextLine());}while (true) {String command = scanner.nextLine();if ("sort1".equals(command)) {sort1(idCards);} else if ("sort2".equals(command)) {sort2(idCards);} else {System.out.println("exit");break;}}scanner.close();}private static void sort1(List<String> idCards) {List<String> dateList = new ArrayList<>();for (String idCard : idCards) {if (idCard.length() >= 14) {String year = idCard.substring(6, 10);String month = idCard.substring(10, 12);String day = idCard.substring(12, 14);dateList.add(year + "-" + month + "-" + day);}}Collections.sort(dateList);for (String date : dateList) {System.out.println(date);}}private static void sort2(List<String> idCards) {List<IdCardWithDate> cardList = new ArrayList<>();for (String idCard : idCards) {if (idCard.length() >= 14) {String dateStr = idCard.substring(6, 14);cardList.add(new IdCardWithDate(idCard, dateStr));}}Collections.sort(cardList, new Comparator<IdCardWithDate>() {public int compare(IdCardWithDate o1, IdCardWithDate o2) {return o1.date.compareTo(o2.date);}});for (IdCardWithDate card : cardList) {System.out.println(card.idCard);}}static class IdCardWithDate {String idCard;String date;public IdCardWithDate(String idCard, String date) {this.idCard = idCard;this.date = date;}}
}

2.3 StringBuilder

点击查看代码

import java.util.Scanner;public class Main {public static void main(String[] args) {Scanner scanner = new Scanner(System.in);while (scanner.hasNextInt()) {int n = scanner.nextInt();int begin = scanner.nextInt();int end = scanner.nextInt();StringBuilder sb = new StringBuilder();for (int i = 0; i < n; i++) {sb.append(i);}String result = sb.substring(begin, end);System.out.println(result);}scanner.close();}
}

2.4 动态数组

点击查看代码

import java.util.Arrays;
import java.util.Scanner;public class Main {public static void main(String[] args) {Scanner scanner = new Scanner(System.in);while (scanner.hasNextInt()) {int n = scanner.nextInt();printMultiplicationTable(n);}scanner.close();}private static void printMultiplicationTable(int n) {String[][] multiplicationTable = new String[n][];for (int i = 1; i <= n; i++) {multiplicationTable[i-1] = new String[i];for (int j = 1; j <= i; j++) {multiplicationTable[i-1][j-1] = i + "*" + j + "=" + (i * j);}}for (int i = 1; i <= n; i++) {for (int j = 1; j <= i; j++) {String item = i + "*" + j + "=" + (i * j);if (j == 1) {System.out.print(item);} else {String prevItem = i + "*" + (j-1) + "=" + (i * (j-1));int totalWidth = 7;int spacesNeeded = totalWidth - prevItem.length();for (int k = 0; k < spacesNeeded; k++) {System.out.print(" ");}System.out.print(item);}}System.out.println();}System.out.println(Arrays.deepToString(multiplicationTable));}
}

**3. PTA实验总结及码云上代码提交记录**

这些实验让我对字符串操作、数组使用和性能优化有了更深入的认识，编程能力也得到了提升。