学习时间： 4-5小时
学习目标： 掌握Java的I/O操作、文件处理、字符串操作和日期时间处理
📋 详细学习清单
✅ 第一部分：输入输出流（I/O Stream）(90分钟)
1. 控制台输入输出
JavaScript (你熟悉的I/O)
javascript
// Node.js 控制台输入
const readline = require('readline');
const rl = readline.createInterface({
input: process.stdin,
output: process.stdout
});
// 异步输入
rl.question('请输入您的姓名: ', (name) => {
console.log(`你好, ${name}!`);
rl.close();
});
// 文件操作
const fs = require('fs');
// 读取文件
fs.readFile('data.txt', 'utf8', (err, data) => {
if (err) throw err;
console.log(data);
});
// 写入文件
fs.writeFile('output.txt', 'Hello World', (err) => {
if (err) throw err;
console.log('文件已保存');
});Java (今天学习的I/O)
java
// ConsoleIO.java
import java.util.Scanner;
import java.io.*;
public class ConsoleIO {
public static void main(String[] args) {
// 1. 控制台输入 - Scanner类
Scanner scanner = new Scanner(System.in);
System.out.print("请输入您的姓名: ");
String name = scanner.nextLine();
System.out.print("请输入您的年龄: ");
int age = scanner.nextInt();
System.out.print("请输入您的身高(米): ");
double height = scanner.nextDouble();
// 输出
System.out.println("=== 个人信息 ===");
System.out.printf("姓名: %s%n", name);
System.out.printf("年龄: %d岁%n", age);
System.out.printf("身高: %.2f米%n", height);
scanner.close();
}
}2. 文件输入输出详解
java
// FileIOExample.java
import java.io.*;
import java.nio.file.*;
import java.util.List;
public class FileIOExample {
public static void main(String[] args) {
// 1. 传统IO方式写入文件
writeFileTraditional();
// 2. NIO方式写入文件
writeFileNIO();
// 3. 读取文件内容
readFileContent();
// 4. 处理二进制文件
copyBinaryFile();
}
// 传统IO写入
public static void writeFileTraditional() {
try (FileWriter writer = new FileWriter("student_info.txt")) {
writer.write("学生信息列表\n");
writer.write("================\n");
writer.write("张三,20,计算机科学\n");
writer.write("李四,21,软件工程\n");
writer.write("王五,19,数据科学\n");
System.out.println("文件写入完成(传统IO)");
} catch (IOException e) {
System.err.println("文件写入失败: " + e.getMessage());
}
}
// NIO写入 (Java 7+)
public static void writeFileNIO() {
try {
String content = "这是使用NIO写入的内容\n" +
"支持更好的性能和功能\n" +
"推荐在新项目中使用";
Path path = Paths.get("nio_example.txt");
Files.write(path, content.getBytes());
System.out.println("文件写入完成(NIO)");
} catch (IOException e) {
System.err.println("NIO写入失败: " + e.getMessage());
}
}
// 读取文件
public static void readFileContent() {
System.out.println("\n=== 读取文件内容 ===");
// 方式1：逐行读取
try (BufferedReader reader = new BufferedReader(new FileReader("student_info.txt"))) {
String line;
int lineNumber = 1;
while ((line = reader.readLine()) != null) {
System.out.printf("%d: %s%n", lineNumber++, line);
}
} catch (IOException e) {
System.err.println("文件读取失败: " + e.getMessage());
}
// 方式2：NIO一次性读取所有行
try {
Path path = Paths.get("nio_example.txt");
List<String> lines = Files.readAllLines(path);
System.out.println("\n=== NIO读取结果 ===");
lines.forEach(System.out::println);
} catch (IOException e) {
System.err.println("NIO读取失败: " + e.getMessage());
}
}
// 复制二进制文件
public static void copyBinaryFile() {
try (FileInputStream fis = new FileInputStream("source.bin");
FileOutputStream fos = new FileOutputStream("copy.bin")) {
byte[] buffer = new byte[1024];
int bytesRead;
while ((bytesRead = fis.read(buffer)) != -1) {
fos.write(buffer, 0, bytesRead);
}
System.out.println("二进制文件复制完成");
} catch (IOException e) {
System.err.println("文件复制失败: " + e.getMessage());
}
}
}💡 实战练习1：学生成绩管理系统
java
// StudentGradeManager.java
import java.io.*;
import java.util.*;
public class StudentGradeManager {
private static final String FILE_NAME = "grades.txt";
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
while (true) {
showMenu();
int choice = scanner.nextInt();
scanner.nextLine(); // 消费换行符
switch (choice) {
case 1 -> addStudent(scanner);
case 2 -> showAllStudents();
case 3 -> searchStudent(scanner);
case 4 -> calculateAverage();
case 5 -> {
System.out.println("程序结束");
return;
}
default -> System.out.println("无效选择，请重新输入");
}
}
}
private static void showMenu() {
System.out.println("\n=== 学生成绩管理系统 ===");
System.out.println("1. 添加学生成绩");
System.out.println("2. 显示所有学生");
System.out.println("3. 查找学生");
System.out.println("4. 计算平均分");
System.out.println("5. 退出");
System.out.print("请选择操作: ");
}
private static void addStudent(Scanner scanner) {
System.out.print("学生姓名: ");
String name = scanner.nextLine();
System.out.print("数学成绩: ");
double math = scanner.nextDouble();
System.out.print("英语成绩: ");
double english = scanner.nextDouble();
System.out.print("Java成绩: ");
double java = scanner.nextDouble();
try (PrintWriter writer = new PrintWriter(new FileWriter(FILE_NAME, true))) {
writer.printf("%s,%.1f,%.1f,%.1f%n", name, math, english, java);
System.out.println("学生信息已保存");
} catch (IOException e) {
System.err.println("保存失败: " + e.getMessage());
}
}
private static void showAllStudents() {
System.out.println("\n=== 所有学生成绩 ===");
System.out.printf("%-10s %-8s %-8s %-8s %-8s%n",
"姓名", "数学", "英语", "Java", "总分");
System.out.println("".repeat(45));
try (BufferedReader reader = new BufferedReader(new FileReader(FILE_NAME))) {
String line;
while ((line = reader.readLine()) != null) {
String[] parts = line.split(",");
if (parts.length == 4) {
String name = parts[0];
double math = Double.parseDouble(parts[1]);
double english = Double.parseDouble(parts[2]);
double java = Double.parseDouble(parts[3]);
double total = math + english + java;
System.out.printf("%-10s %-8.1f %-8.1f %-8.1f %-8.1f%n",
name, math, english, java, total);
}
}
} catch (IOException e) {
System.err.println("读取失败: " + e.getMessage());
}
}
private static void searchStudent(Scanner scanner) {
System.out.print("输入要查找的学生姓名: ");
String searchName = scanner.nextLine();
boolean found = false;
try (BufferedReader reader = new BufferedReader(new FileReader(FILE_NAME))) {
String line;
while ((line = reader.readLine()) != null) {
String[] parts = line.split(",");
if (parts.length == 4 && parts[0].equals(searchName)) {
System.out.println("\n=== 找到学生信息 ===");
System.out.println("姓名: " + parts[0]);
System.out.println("数学: " + parts[1]);
System.out.println("英语: " + parts[2]);
System.out.println("Java: " + parts[3]);
double total = Double.parseDouble(parts[1]) +
Double.parseDouble(parts[2]) +
Double.parseDouble(parts[3]);
System.out.printf("总分: %.1f%n", total);
System.out.printf("平均分: %.1f%n", total / 3);
found = true;
break;
}
}
if (!found) {
System.out.println("未找到该学生");
}
} catch (IOException e) {
System.err.println("查找失败: " + e.getMessage());
}
}
private static void calculateAverage() {
double totalMath = 0, totalEnglish = 0, totalJava = 0;
int count = 0;
try (BufferedReader reader = new BufferedReader(new FileReader(FILE_NAME))) {
String line;
while ((line = reader.readLine()) != null) {
String[] parts = line.split(",");
if (parts.length == 4) {
totalMath += Double.parseDouble(parts[1]);
totalEnglish += Double.parseDouble(parts[2]);
totalJava += Double.parseDouble(parts[3]);
count++;
}
}
if (count > 0) {
System.out.println("\n=== 班级平均分 ===");
System.out.printf("数学平均分: %.1f%n", totalMath / count);
System.out.printf("英语平均分: %.1f%n", totalEnglish / count);
System.out.printf("Java平均分: %.1f%n", totalJava / count);
System.out.printf("总体平均分: %.1f%n",
(totalMath + totalEnglish + totalJava) / (count * 3));
} else {
System.out.println("暂无学生数据");
}
} catch (IOException e) {
System.err.println("计算失败: " + e.getMessage());
}
}
}✅ 第二部分：字符串深度处理 (80分钟)
1. String vs StringBuilder vs StringBuffer
JavaScript (你熟悉的字符串)
javascript
// JavaScript 字符串操作
let str = "Hello";
str += " World"; // 创建新字符串
str += "!"; // 再次创建新字符串
// 模板字符串
const name = "张三";
const age = 25;
const message = `你好，${name}，你今年${age}岁`;
// 字符串方法
const text = " Hello World ";
console.log(text.trim()); // "Hello World"
console.log(text.toUpperCase()); // " HELLO WORLD "
console.log(text.split(" ")); // ["", "", "Hello", "World", "", ""]Java (今天学习的字符串)
java
// StringComparison.java
public class StringComparison {
public static void main(String[] args) {
// 1. String - 不可变字符串
demonstrateString();
// 2. StringBuilder - 可变字符串(非线程安全)
demonstrateStringBuilder();
// 3. StringBuffer - 可变字符串(线程安全)
demonstrateStringBuffer();
// 4. 性能对比
performanceComparison();
}
public static void demonstrateString() {
System.out.println("=== String演示 ===");
String str1 = "Hello";
String str2 = " World";
String result = str1 + str2; // 创建新的String对象
System.out.println("原始字符串str1: " + str1); // "Hello" 不变
System.out.println("拼接结果: " + result); // "Hello World"
// 字符串常用方法
String text = " Java Programming ";
System.out.println("原始: '" + text + "'");
System.out.println("长度: " + text.length());
System.out.println("去除空格: '" + text.trim() + "'");
System.out.println("转大写: '" + text.toUpperCase() + "'");
System.out.println("转小写: '" + text.toLowerCase() + "'");
System.out.println("是否包含Java: " + text.contains("Java"));
System.out.println("替换Java为Python: " + text.replace("Java", "Python"));
// 字符串分割
String csv = "张三,25,北京,工程师";
String[] parts = csv.split(",");
System.out.println("分割结果:");
for (int i = 0; i < parts.length; i++) {
System.out.printf(" [%d]: %s%n", i, parts[i]);
}
}
public static void demonstrateStringBuilder() {
System.out.println("\n=== StringBuilder演示 ===");
StringBuilder sb = new StringBuilder();
sb.append("Hello");
sb.append(" ");
sb.append("World");
sb.append("!");
System.out.println("构建的字符串: " + sb.toString());
// StringBuilder常用方法
sb.insert(5, " Beautiful"); // 在索引5处插入
System.out.println("插入后: " + sb.toString());
sb.delete(5, 15); // 删除索引5-15的字符
System.out.println("删除后: " + sb.toString());
sb.reverse(); // 反转字符串
System.out.println("反转后: " + sb.toString());
sb.reverse(); // 再次反转回来
System.out.println("恢复后: " + sb.toString());
// 链式调用
StringBuilder chain = new StringBuilder()
.append("Java")
.append(" is")
.append(" awesome")
.append("!");
System.out.println("链式调用结果: " + chain.toString());
}
public static void demonstrateStringBuffer() {
System.out.println("\n=== StringBuffer演示 ===");
StringBuffer buffer = new StringBuffer("Initial");
buffer.append(" Text");
buffer.insert(7, " Modified");
System.out.println("StringBuffer结果: " + buffer.toString());
System.out.println("长度: " + buffer.length());
System.out.println("容量: " + buffer.capacity());
}
public static void performanceComparison() {
System.out.println("\n=== 性能对比 ===");
int iterations = 10000;
// String拼接性能测试
long startTime = System.currentTimeMillis();
String str = "";
for (int i = 0; i < iterations; i++) {
str += "a"; // 每次都创建新对象
}
long stringTime = System.currentTimeMillis() - startTime;
// StringBuilder性能测试
startTime = System.currentTimeMillis();
StringBuilder sb = new StringBuilder();
for (int i = 0; i < iterations; i++) {
sb.append("a"); // 在同一对象上操作
}
long sbTime = System.currentTimeMillis() - startTime;
System.out.printf("String拼接%d次耗时: %d毫秒%n", iterations, stringTime);
System.out.printf("StringBuilder拼接%d次耗时: %d毫秒%n", iterations, sbTime);
System.out.printf("StringBuilder比String快 %.1f 倍%n",
(double)stringTime / sbTime);
}
}2. 字符串格式化与正则表达式
java
// StringFormatAndRegex.java
import java.util.regex.*;
import java.text.DecimalFormat;
public class StringFormatAndRegex {
public static void main(String[] args) {
// 1. 字符串格式化
demonstrateStringFormat();
// 2. 正则表达式
demonstrateRegularExpressions();
// 3. 数字格式化
demonstrateNumberFormat();
}
public static void demonstrateStringFormat() {
System.out.println("=== 字符串格式化 ===");
String name = "张三";
int age = 25;
double salary = 12345.678;
// printf风格格式化
System.out.printf("姓名: %s, 年龄: %d, 薪资: %.2f%n", name, age, salary);
// String.format方法
String formatted = String.format("员工 %s 今年 %d 岁，月薪 ¥%.2f",
name, age, salary);
System.out.println(formatted);
// 其他格式化选项
System.out.printf("左对齐: %-10s|%n", name);
System.out.printf("右对齐: %10s|%n", name);
System.out.printf("补零: %08d%n", 123);
System.out.printf("科学记数法: %e%n", 123456.789);
System.out.printf("百分比: %.1f%%%n", 0.85 * 100);
}
public static void demonstrateRegularExpressions() {
System.out.println("\n=== 正则表达式 ===");
// 1. 基本匹配
String email = "[email protected]";
String emailPattern = "^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\\.[a-zA-Z]{2,}$";
boolean isValidEmail = Pattern.matches(emailPattern, email);
System.out.println("邮箱 " + email + " 有效性: " + isValidEmail);
// 2. 手机号验证
String[] phones = {"13812345678", "1381234567", "138123456789", "12812345678"};
String phonePattern = "^1[3-9]\\d{9}$";
System.out.println("\n手机号验证:");
for (String phone : phones) {
boolean isValid = Pattern.matches(phonePattern, phone);
System.out.printf("%s: %s%n", phone, isValid ? "有效" : "无效");
}
// 3. 查找和替换
String text = "今天是2023年12月25日，明天是2023年12月26日";
String datePattern = "(\\d{4})年(\\d{1,2})月(\\d{1,2})日";
Pattern pattern = Pattern.compile(datePattern);
Matcher matcher = pattern.matcher(text);
System.out.println("\n找到的日期:");
while (matcher.find()) {
System.out.printf("完整匹配: %s%n", matcher.group(0));
System.out.printf("年: %s, 月: %s, 日: %s%n",
matcher.group(1), matcher.group(2), matcher.group(3));
}
// 替换日期格式
String replaced = text.replaceAll(datePattern, "$1-$2-$3");
System.out.println("替换后: " + replaced);
// 4. 分割字符串
String data = "apple,banana;orange:grape|peach";
String[] fruits = data.split("[,;:|]"); // 多个分隔符
System.out.println("\n水果列表:");
for (String fruit : fruits) {
System.out.println("- " + fruit);
}
}
public static void demonstrateNumberFormat() {
System.out.println("\n=== 数字格式化 ===");
double number = 123456.789;
// DecimalFormat格式化
DecimalFormat df1 = new DecimalFormat("#,###.##");
System.out.println("千分位分隔: " + df1.format(number));
DecimalFormat df2 = new DecimalFormat("¥#,###.00");
System.out.println("货币格式: " + df2.format(number));
DecimalFormat df3 = new DecimalFormat("000000.000");
System.out.println("补零格式: " + df3.format(number));
// 百分比格式
DecimalFormat percent = new DecimalFormat("#.##%");
System.out.println("百分比: " + percent.format(0.856));
}
}💡 实战练习2：文本处理工具
java
// TextProcessor.java
import java.util.*;
import java.util.regex.*;
public class TextProcessor {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
System.out.println("=== 文本处理工具 ===");
System.out.print("请输入一段文本: ");
String text = scanner.nextLine();
// 1. 基本统计
analyzeText(text);
// 2. 单词频率统计
countWordFrequency(text);
// 3. 格式化处理
formatText(text);
// 4. 敏感词过滤
filterSensitiveWords(text);
scanner.close();
}
public static void analyzeText(String text) {
System.out.println("\n=== 文本统计 ===");
int totalChars = text.length();
int nonSpaceChars = text.replaceAll("\\s", "").length();
int words = text.trim().isEmpty() ? 0 : text.trim().split("\\s+").length;
int lines = text.split("\n").length;
int sentences = text.split("[.!?]+").length;
System.out.println("总字符数: " + totalChars);
System.out.println("非空字符数: " + nonSpaceChars);
System.out.println("单词数: " + words);
System.out.println("行数: " + lines);
System.out.println("句子数: " + sentences);
// 字符分布统计
Map<Character, Integer> charCount = new HashMap<>();
for (char c : text.toLowerCase().toCharArray()) {
if (Character.isLetter(c)) {
charCount.put(c, charCount.getOrDefault(c, 0) + 1);
}
}
System.out.println("\n字母频率 (前5位):");
charCount.entrySet().stream()
.sorted(Map.Entry.<Character, Integer>comparingByValue().reversed())
.limit(5)
.forEach(entry ->
System.out.printf("%c: %d次%n", entry.getKey(), entry.getValue()));
}
public static void countWordFrequency(String text) {
System.out.println("\n=== 单词频率 ===");
// 提取单词（去除标点符号）
String[] words = text.toLowerCase()
.replaceAll("[^a-zA-Z\\s\\u4e00-\\u9fa5]", "")
.split("\\s+");
Map<String, Integer> wordCount = new HashMap<>();
for (String word : words) {
if (!word.trim().isEmpty()) {
wordCount.put(word.trim(), wordCount.getOrDefault(word.trim(), 0) + 1);
}
}
System.out.println("单词频率统计 (前10位):");
wordCount.entrySet().stream()
.sorted(Map.Entry.<String, Integer>comparingByValue().reversed())
.limit(10)
.forEach(entry ->
System.out.printf("%-10s: %d次%n", entry.getKey(), entry.getValue()));
}
public static void formatText(String text) {
System.out.println("\n=== 文本格式化 ===");
// 1. 标准化空格
String normalized = text.replaceAll("\\s+", " ").trim();
System.out.println("标准化空格: " + normalized);
// 2. 首字母大写
String capitalized = Arrays.stream(normalized.split("\\s+"))
.map(word -> {
if (word.length() > 0) {
return Character.toUpperCase(word.charAt(0)) +
word.substring(1).toLowerCase();
}
return word;
})
.reduce("", (a, b) -> a.isEmpty() ? b : a + " " + b);
System.out.println("首字母大写: " + capitalized);
// 3. 驼峰命名
String camelCase = Arrays.stream(normalized.split("\\s+"))
.map(word -> Character.toUpperCase(word.charAt(0)) +
word.substring(1).toLowerCase())
.reduce("", String::concat);
System.out.println("驼峰命名: " + camelCase);
// 4. 下划线命名
String snakeCase = normalized.toLowerCase().replaceAll("\\s+", "_");
System.out.println("下划线命名: " + snakeCase);
}
public static void filterSensitiveWords(String text) {
System.out.println("\n=== 敏感词过滤 ===");
// 敏感词列表（示例）
String[] sensitiveWords = {"坏蛋", "笨蛋", "傻瓜"};
String filtered = text;
for (String word : sensitiveWords) {
if (filtered.contains(word)) {
String replacement = "*".repeat(word.length());
filtered = filtered.replace(word, replacement);
System.out.printf("发现敏感词: %s -> %s%n", word, replacement);
}
}
System.out.println("过滤后文本: " + filtered);
// 使用正则表达式批量替换
String regexFiltered = text.replaceAll("(?i)(坏蛋|笨蛋|傻瓜)", "***");
System.out.println("正则过滤结果: " + regexFiltered);
}
}✅ 第三部分：日期时间处理 (50分钟)
1. 新旧API对比
java
// DateTimeExample.java
import java.time.*;
import java.time.format.DateTimeFormatter;
import java.time.temporal.ChronoUnit;
import java.util.*;
public class DateTimeExample {
public static void main(String[] args) {
// 1. 新API使用 (Java 8+)
demonstrateNewDateTimeAPI();
// 2. 日期计算
demonstrateDateCalculations();
// 3. 日期格式化
demonstrateDateFormatting();
// 4. 时区处理
demonstrateTimeZones();
}
public static void demonstrateNewDateTimeAPI() {
System.out.println("=== Java 8+ 日期时间API ===");
// 获取当前日期时间
LocalDate today = LocalDate.now();
LocalTime now = LocalTime.now();
LocalDateTime dateTime = LocalDateTime.now();
Instant instant = Instant.now();
System.out.println("当前日期: " + today);
System.out.println("当前时间: " + now);
System.out.println("当前日期时间: " + dateTime);
System.out.println("时间戳: " + instant);
// 创建特定日期时间
LocalDate birthday = LocalDate.of(1995, 6, 15);
LocalTime meeting = LocalTime.of(14, 30, 0);
LocalDateTime appointment = LocalDateTime.of(2024, 1, 15, 10, 30);
System.out.println("生日: " + birthday);
System.out.println("会议时间: " + meeting);
System.out.println("预约时间: " + appointment);
// 解析字符串
LocalDate parsed1 = LocalDate.parse("2024-01-15");
LocalDateTime parsed2 = LocalDateTime.parse("2024-01-15T10:30:00");
System.out.println("解析日期: " + parsed1);
System.out.println("解析日期时间: " + parsed2);
}
public static void demonstrateDateCalculations() {
System.out.println("\n=== 日期计算 ===");
LocalDate today = LocalDate.now();
// 日期加减
LocalDate tomorrow = today.plusDays(1);
LocalDate nextWeek = today.plusWeeks(1);
LocalDate nextMonth = today.plusMonths(1);
LocalDate nextYear = today.plusYears(1);
System.out.println("今天: " + today);
System.out.println("明天: " + tomorrow);
System.out.println("下周: " + nextWeek);
System.out.println("下月: " + nextMonth);
System.out.println("明年: " + nextYear);
// 日期差计算
LocalDate startDate = LocalDate.of(2024, 1, 1);
LocalDate endDate = LocalDate.of(2024, 12, 31);
long daysBetween = ChronoUnit.DAYS.between(startDate, endDate);
long weeksBetween = ChronoUnit.WEEKS.between(startDate, endDate);
long monthsBetween = ChronoUnit.MONTHS.between(startDate, endDate);
System.out.printf("%s 到 %s:%n", startDate, endDate);
System.out.printf("相差 %d 天%n", daysBetween);
System.out.printf("相差 %d 周%n", weeksBetween);
System.out.printf("相差 %d 月%n", monthsBetween);
// 判断日期关系
LocalDate date1 = LocalDate.of(2024, 6, 15);
LocalDate date2 = LocalDate.of(2024, 6, 20);
System.out.printf("%s 在 %s 之前: %b%n", date1, date2, date1.isBefore(date2));
System.out.printf("%s 在 %s 之后: %b%n", date1, date2, date1.isAfter(date2));
System.out.printf("今年是闰年: %b%n", today.isLeapYear());
}
public static void demonstrateDateFormatting() {
System.out.println("\n=== 日期格式化 ===");
LocalDateTime now = LocalDateTime.now();
// 预定义格式
System.out.println("ISO格式: " + now.format(DateTimeFormatter.ISO_LOCAL_DATE_TIME));
// 自定义格式
DateTimeFormatter formatter1 = DateTimeFormatter.ofPattern("yyyy年MM月dd日 HH:mm:ss");
System.out.println("中文格式: " + now.format(formatter1));
DateTimeFormatter formatter2 = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
System.out.println("标准格式: " + now.format(formatter2));
DateTimeFormatter formatter3 = DateTimeFormatter.ofPattern("MM/dd/yyyy hh:mm a");
System.out.println("美式格式: " + now.format(formatter3));
// 只格式化日期或时间
DateTimeFormatter dateFormatter = DateTimeFormatter.ofPattern("yyyy年MM月dd日");
DateTimeFormatter timeFormatter = DateTimeFormatter.ofPattern("HH:mm:ss");
System.out.println("仅日期: " + now.format(dateFormatter));
System.out.println("仅时间: " + now.format(timeFormatter));
// 解析自定义格式
String dateString = "2024年1月15日 14:30:00";
LocalDateTime parsed = LocalDateTime.parse(dateString, formatter1);
System.out.println("解析结果: " + parsed);
}
public static void demonstrateTimeZones() {
System.out.println("\n=== 时区处理 ===");
// 当前时区时间
ZonedDateTime currentZone = ZonedDateTime.now();
System.out.println("当前时区: " + currentZone);
// 不同时区的相同时刻
ZonedDateTime beijing = ZonedDateTime.now(ZoneId.of("Asia/Shanghai"));
ZonedDateTime tokyo = ZonedDateTime.now(ZoneId.of("Asia/Tokyo"));
ZonedDateTime london = ZonedDateTime.now(ZoneId.of("Europe/London"));
ZonedDateTime newYork = ZonedDateTime.now(ZoneId.of("America/New_York"));
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("HH:mm:ss (zzz)");
System.out.println("北京时间: " + beijing.format(formatter));
System.out.println("东京时间: " + tokyo.format(formatter));
System.out.println("伦敦时间: " + london.format(formatter));
System.out.println("纽约时间: " + newYork.format(formatter));
// 时区转换
ZonedDateTime beijingMeeting = ZonedDateTime.of(
2024, 1, 15, 14, 0, 0, 0,
ZoneId.of("Asia/Shanghai")
);
ZonedDateTime newYorkTime = beijingMeeting.withZoneSameInstant(
ZoneId.of("America/New_York")
);
System.out.printf("北京时间 %s 对应纽约时间 %s%n",
beijingMeeting.format(formatter),
newYorkTime.format(formatter));
}
}📚 今日作业与练习
作业1：个人日记系统
创建一个简单的日记系统，要求：
- 用户可以写入日记（包含日期、心情、内容）
- 可以按日期查看历史日记
- 支持关键词搜索日记内容
- 日记保存到文件中
作业2：文本分析工具
编写程序分析一篇文章：
- 统计字数、句数、段落数
- 找出最常用的10个单词
- 检查文本中的邮箱地址和电话号码
- 生成文本摘要（截取前100个字符）
作业3：日程管理器
实现简单的日程管理功能：
- 添加日程（标题、时间、地点、描述）
- 查看今日/明日/本周日程
- 日程提醒（距离开始时间的倒计时）
- 支持日程的修改和删除
🎯 明日预告：第6天
学习内容：
- 多线程编程基础
- 线程同步与锁机制
- 线程池的使用
- 并发集合类
重点技能：
- 理解线程概念
- 掌握synchronized关键字
- 学会使用ExecutorService
- 避免常见的并发问题