From c0ff930024f2ff955b220a6c451d96b25bd21afc Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E6=A0=91=E8=90=8C=E8=8A=BD?= <3205788256@qq.com>
Date: Mon, 22 Sep 2025 21:36:32 +0800
Subject: [PATCH] =?UTF-8?q?9=E6=9C=8822=E6=97=A5=E5=AD=A6=E4=B9=A0?=
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Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
---
src/main/java/smy/javastudy/Main.java | 71 ++++++++---
.../java/smy/javastudy/TestNumberClass.java | 27 ----
.../java/smy/javastudy/aiwrite/MathUtils.java | 24 ++++
.../{ => aiwrite}/NumberAndMathDemo.java | 4 +-
.../smy/javastudy/classes/CharacterClass.java | 48 +++++++
.../java/smy/javastudy/classes/MathClass.java | 59 +++++++++
.../smy/javastudy/classes/NumberClass.java | 65 ++++++++++
.../javastudy/classes/StringBufferClass.java | 49 ++++++++
.../smy/javastudy/classes/StringClass.java | 117 ++++++++++++++++++
9 files changed, 421 insertions(+), 43 deletions(-)
delete mode 100644 src/main/java/smy/javastudy/TestNumberClass.java
create mode 100644 src/main/java/smy/javastudy/aiwrite/MathUtils.java
rename src/main/java/smy/javastudy/{ => aiwrite}/NumberAndMathDemo.java (98%)
create mode 100644 src/main/java/smy/javastudy/classes/CharacterClass.java
create mode 100644 src/main/java/smy/javastudy/classes/MathClass.java
create mode 100644 src/main/java/smy/javastudy/classes/NumberClass.java
create mode 100644 src/main/java/smy/javastudy/classes/StringBufferClass.java
create mode 100644 src/main/java/smy/javastudy/classes/StringClass.java
diff --git a/src/main/java/smy/javastudy/Main.java b/src/main/java/smy/javastudy/Main.java
index 0c6d5df..1bc1db8 100644
--- a/src/main/java/smy/javastudy/Main.java
+++ b/src/main/java/smy/javastudy/Main.java
@@ -1,6 +1,8 @@
package smy.javastudy;
+import smy.javastudy.aiwrite.NumberAndMathDemo;
+import smy.javastudy.classes.*;
public class Main {
final double PI = 3.14159;
@@ -10,23 +12,64 @@ public class Main {
//项目唯一主函数
public static void main(String[] args) {
- //TIP 当文本光标位于高亮显示的文本处时按
- // 查看 IntelliJ IDEA 建议如何修正。
- System.out.printf("Hello and welcome!\n");
- Main main = new Main();
- main.testHuHangTao();
+ //测试本地方法
+ if(false){
+ System.out.printf("Hello and welcome!\n");
+ Main main = new Main();
+ main.testHuHangTao();
+ }
- JavaBasicDataType dataType = new JavaBasicDataType();
- dataType.ShowDataTypesInfo();
- GrammarPractice grammarPractice = new GrammarPractice();
- grammarPractice.Exchange("刘道熙");
- grammarPractice.Exchange("唐伟");
- grammarPractice.Exchange("树萌芽");
+ //测试基本数据类型
+ if(false){
+ JavaBasicDataType dataType = new JavaBasicDataType();
+ dataType.ShowDataTypesInfo();
+ }
+
+
+ //测试基本语法
+ if(false){
+ GrammarPractice grammarPractice = new GrammarPractice();
+ grammarPractice.Exchange("刘道熙");
+ grammarPractice.Exchange("唐伟");
+ grammarPractice.Exchange("树萌芽");
+
+ }
+
+
+ //ai写的Number类和Math类的用法
+ if(false){
+ NumberAndMathDemo demo = new NumberAndMathDemo();
+ demo.numberClassUsage();
+ demo.mathClassUsage();
+ }
+
+ //测试Number类和Math类用法
+ if (false){
+ MathClass mathClass = new MathClass();
+ mathClass.MathClass();
+ NumberClass numberClass = new NumberClass();
+ numberClass.NumberClass();
+ }
+
+ //测试Charactor类用法
+ if(false){
+ CharacterClass characterClass = new CharacterClass();
+ characterClass.CharacterClass();
+ }
+
+ //测试String类用法
+ if(false){
+ StringClass stringClass = new StringClass();
+ stringClass.StringClass();
+ }
+
+ //测试StringBuffer
+ if (true){
+ StringBufferClass stringBufferClass = new StringBufferClass();
+ stringBufferClass.StringBufferClass();
+ }
- NumberAndMathDemo demo = new NumberAndMathDemo();
- demo.numberClassUsage();
- demo.mathClassUsage();
}
public void testHuHangTao(){
diff --git a/src/main/java/smy/javastudy/TestNumberClass.java b/src/main/java/smy/javastudy/TestNumberClass.java
deleted file mode 100644
index 8f7ed66..0000000
--- a/src/main/java/smy/javastudy/TestNumberClass.java
+++ /dev/null
@@ -1,27 +0,0 @@
-package smy.javastudy;
-import java.lang.Number;
-
-public class TestNumberClass {
-
- //基本类型转换
- public void typeConversion(){
- Number num1 = 1234.56;
- System.out.println(num1);
- System.out.println(num1.getClass());
- System.out.println(num1.intValue());
- System.out.println(num1.longValue());
- System.out.println(num1.doubleValue());
- System.out.println(num1.floatValue());
- System.out.println(num1.byteValue());
- }
-
- //数值比较
- public void compareNum(){
- Integer x = 10;
- Double y = 10.0;
- System.out.println(x.doubleValue()==y.doubleValue());
- }
-
- //处理大数
- //public
-}
diff --git a/src/main/java/smy/javastudy/aiwrite/MathUtils.java b/src/main/java/smy/javastudy/aiwrite/MathUtils.java
new file mode 100644
index 0000000..9bb07a1
--- /dev/null
+++ b/src/main/java/smy/javastudy/aiwrite/MathUtils.java
@@ -0,0 +1,24 @@
+package smy.javastudy.aiwrite;
+
+public class MathUtils {
+
+ // 使用泛型方法，支持所有Number子类（Integer, Long, Float, Double等）
+ public static double log(T base, U value) {
+ // 将泛型参数转换为double进行计算
+ double baseDouble = base.doubleValue();
+ double valueDouble = value.doubleValue();
+
+ // 参数校验
+ if (baseDouble <= 0 || baseDouble == 1) {
+ throw new IllegalArgumentException("底数必须是正数且不等于1");
+ }
+ if (valueDouble <= 0) {
+ throw new IllegalArgumentException("对数值必须是正数");
+ }
+
+ // 计算并返回结果
+ return Math.log(valueDouble) / Math.log(baseDouble);
+ }
+
+}
+
diff --git a/src/main/java/smy/javastudy/NumberAndMathDemo.java b/src/main/java/smy/javastudy/aiwrite/NumberAndMathDemo.java
similarity index 98%
rename from src/main/java/smy/javastudy/NumberAndMathDemo.java
rename to src/main/java/smy/javastudy/aiwrite/NumberAndMathDemo.java
index fd4f4a1..4853859 100644
--- a/src/main/java/smy/javastudy/NumberAndMathDemo.java
+++ b/src/main/java/smy/javastudy/aiwrite/NumberAndMathDemo.java
@@ -1,4 +1,4 @@
-package smy.javastudy;
+package smy.javastudy.aiwrite;
import java.math.BigDecimal;
import java.math.BigInteger;
@@ -84,6 +84,6 @@ public class NumberAndMathDemo {
// 获取一个范围内的随机整数，例如 [1, 10]
int randomInt = (int) (Math.random() * 10) + 1;
System.out.println("一个 1 到 10 之间的随机整数: " + randomInt);
- System.out.println("\n=========================Math类的用法=========================");
+ System.out.println("\n=========================Math类的用法=========================\n");
}
}
diff --git a/src/main/java/smy/javastudy/classes/CharacterClass.java b/src/main/java/smy/javastudy/classes/CharacterClass.java
new file mode 100644
index 0000000..e45dba4
--- /dev/null
+++ b/src/main/java/smy/javastudy/classes/CharacterClass.java
@@ -0,0 +1,48 @@
+package smy.javastudy.classes;
+
+public class CharacterClass {
+ public void CharacterClass() {
+ System.out.println("\n=========================Character类的用法=========================");
+ char ch1 = 'a';
+ char ch2 = '1';
+ char ch3 = ' ';
+ char ch4 = '\n';
+ char ch5 = '中';
+
+ // 判断字符类型
+ System.out.println(ch1 + " 是字母吗? " + Character.isLetter(ch1));
+ System.out.println(ch2 + " 是数字吗? " + Character.isDigit(ch2));
+ System.out.println(ch3 + " 是空白吗? " + Character.isWhitespace(ch3));
+ System.out.println(ch4 + " 是空白吗? " + Character.isWhitespace(ch4));
+ System.out.println(ch5 + " 是汉字吗? " + Character.isIdeographic(ch5));
+
+ // 字符转换
+ System.out.println(ch1 + " 转为大写: " + Character.toUpperCase(ch1));
+ System.out.println(Character.toUpperCase('A') + " 转为小写: " + Character.toLowerCase('A'));
+ System.out.println("9 转为数字: " + Character.getNumericValue('9'));
+ System.out.println("A 转为数字: " + Character.getNumericValue('A')); // A对应10
+
+ // 获取字符信息
+ System.out.println("Unicode 码点 of '" + ch5 + "': " + (int) ch5);
+ System.out.println("字符 '" + ch1 + "' 的类别: " + Character.getType(ch1)); // 0-控制字符，1-大写字母，2-小写字母，9-数字等
+
+ // 判断字符是否为特定类型
+ System.out.println('A' + " 是大写字母吗? " + Character.isUpperCase('A'));
+ System.out.println('a' + " 是小写字母吗? " + Character.isLowerCase('a'));
+
+ // 其他有用的方法
+ System.out.println("空字符 '\\0' 的 Unicode 码点: " + (int) '\0');
+ System.out.println("回车符 '\\r' 的 Unicode 码点: " + (int) '\r');
+ System.out.println("制表符 '\\t' 的 Unicode 码点: " + (int) '\t');
+
+ //测试转义字符
+ System.out.println("/t 效果为: Hello\tWorld!");//制表符
+ System.out.println("/n 效果为: Hello\nWorld!");//换行符
+ System.out.println("/r 效果为: Hello\rWorld!");//回车符
+ System.out.println("/' 效果为: It\'s a nice day!");//单引号
+ System.out.println("/" + " 效果为: He said, \"" + "Hello!\"");//双引号
+ System.out.println("/ 效果为: This is a backslash: \\");//反斜杠
+ System.out.println("访问\"菜鸟教程!\"");
+ System.out.println("=========================Character类的用法=========================\n");
+ }
+}
diff --git a/src/main/java/smy/javastudy/classes/MathClass.java b/src/main/java/smy/javastudy/classes/MathClass.java
new file mode 100644
index 0000000..0cee682
--- /dev/null
+++ b/src/main/java/smy/javastudy/classes/MathClass.java
@@ -0,0 +1,59 @@
+package smy.javastudy.classes;
+
+import smy.javastudy.aiwrite.MathUtils;
+
+//数学类的简单举例
+public class MathClass {
+
+ public void MathClass() {
+ System.out.println("\n=========================Math类的用法=========================");
+ double x = 45.6;
+ double y = -78.9;
+ double angle = 45.0;
+
+ // 基本算术方法
+ System.out.println(y + " 的绝对值是: " + Math.abs(y));
+ System.out.println(x + " 的向上取整是: " + Math.ceil(x)); // 向上取整
+ System.out.println(x + " 的向下取整是: " + Math.floor(x)); // 向下取整
+ System.out.println(x + " 的四舍五入是: " + Math.round(x)); // 四舍五入到最近的整数
+ System.out.println(x + " 和 " + y + " 的最大值是: " + Math.max(x, y));
+ System.out.println(x + " 和 " + y + " 的最小值是: " + Math.min(x, y));
+
+ // 指数和对数函数
+ System.out.println("e^2 是: " + Math.exp(2));
+ System.out.println("10 的自然对数是: " + Math.log(10));//ln10
+ System.out.println("100 的以10为底的对数是: " + Math.log10(100));//lg100
+ System.out.println("1000 的以2为底的对数是: " + (Math.log(1000)/Math.log(2)));//以2为底的对数可以用换底公式计算
+ System.out.println("10000 的以5为底的对数是: " + (MathUtils.log(10000,5)));//
+ System.out.println("2^3 是: " + Math.pow(2, 3));
+ System.out.println("16 的平方根是: " + Math.sqrt(16));
+
+ // 三角函数
+ double radians = Math.toRadians(angle);
+ System.out.println(angle + " 度的正弦值是: " + Math.sin(radians));
+ System.out.println(angle + " 度的余弦值是: " + Math.cos(radians));
+ System.out.println(angle + " 度的正切值是: " + Math.tan(radians));
+ System.out.println("将 " + radians + " 弧度转换为度: " + Math.toDegrees(radians));
+ System.out.println("1的反正切值: " + Math.atan(1));//反正切值
+
+ // 随机数生成
+ // Math.random() 返回一个大于等于 0.0 且小于 1.0 的 double 值 [0,1)
+ System.out.println("一个随机数: " + Math.random());
+ // 获取一个范围内的随机整数，例如 [1, 10]
+ int randomInt = (int) (Math.random() * 10) + 1;
+ System.out.println("一个 1 到 10 之间的随机整数: " + randomInt);
+
+ // 其他有用的方法
+ System.out.println("符号函数:"+Math.signum(-23.45));//返回数字的符号，负数返回-1.0，正数返回1.0，零返回0.0 → -1.0
+ System.out.println("平方和开根:"+Math.hypot(3,4));//计算sqrt(3²+5²) → 5.0
+ System.out.println("返回余数"+Math.IEEEremainder(10,3));//返回10除以3的余数，结果可能为负数 → 1.0
+ System.out.println("指数运算:"+Math.getExponent(256.0));//返回256的指数部分 → 8
+ System.out.println("2的3次方:"+Math.scalb(2,3));//返回2乘以2的3次方 → 16.0
+ System.out.println("转换成字符串: " + Math.random());//返回"java.lang.Math"
+ System.out.println("字串符解析成整数数值:"+Integer.parseInt("123123123"));//返回123123123
+ System.out.println("字串符解析成浮点数值:"+Double.parseDouble("123.123123"));//返回123.123123;
+ System.out.println("=========================Math类的用法=========================\n");
+
+ }
+
+}
diff --git a/src/main/java/smy/javastudy/classes/NumberClass.java b/src/main/java/smy/javastudy/classes/NumberClass.java
new file mode 100644
index 0000000..a74b847
--- /dev/null
+++ b/src/main/java/smy/javastudy/classes/NumberClass.java
@@ -0,0 +1,65 @@
+package smy.javastudy.classes;
+import java.lang.Number;
+import java.math.BigDecimal;
+import java.math.BigInteger;
+import java.text.NumberFormat;
+
+public class NumberClass {
+
+ //基本类型转换
+ public void NumberClass(){
+ System.out.println("\n=========================Number类的用法=========================");
+ Number num1 = 1234.56;
+ System.out.println(num1);
+ System.out.println(num1.getClass());
+ System.out.println(num1.intValue());
+ System.out.println(num1.longValue());
+ System.out.println(num1.doubleValue());
+ System.out.println(num1.floatValue());
+ System.out.println(num1.byteValue());
+
+
+ //数值比较
+ Integer x = 10;
+ Double y = 10.0;
+ System.out.println(x.doubleValue()==y.doubleValue());
+
+ //大数用法
+ BigInteger bigInt1 = new BigInteger("123122222222222222222222231231231231231");
+ BigInteger bigInt2 = new BigInteger("9876543210987654321098765432109876543210");
+ BigInteger resInt1 = bigInt1.add(bigInt2); //相加 注意：BigInteger 和 BigDecimal 的加减乘除不能用 + - * / 这些运算符
+ BigInteger resInt2 = bigInt1.multiply(bigInt2);//相乘
+ BigInteger resInt3 = bigInt1.subtract(bigInt2);//相减
+ BigInteger resInt4 = bigInt1.divide(bigInt2);//相除
+ System.out.println("大整数相加"+resInt1);
+ System.out.println("大整数相乘"+resInt2);
+ System.out.println("大整数想减"+resInt3);
+ System.out.println("大整数相除"+resInt4);
+
+ BigDecimal bigDec1 = new BigDecimal("1293123.123123123123123123123");
+ BigDecimal bigDec2 = new BigDecimal("98765.4321098765432109876543210");
+ BigDecimal resDec1 = bigDec1.add(bigDec2);
+ BigDecimal resDec2 = bigDec1.multiply(bigDec2);
+ BigDecimal resDec3 = bigDec1.subtract(bigDec2);
+ BigDecimal resDec4 = bigDec1.divide(bigDec2, 10, BigDecimal.ROUND_HALF_UP); // 指定小数位数和舍入模式，避免异常
+ System.out.println("大浮点数相加"+resDec1);
+ System.out.println("大浮点数相乘"+resDec2);
+ System.out.println("大浮点数相减"+resDec3);
+ System.out.println("大浮点数相除"+resDec4);
+
+ // compareTo() 方法 (来自 Comparable 接口, 由 Number 的子类实现)
+ Integer int1 = 100;
+ Integer int2 = 200;
+ System.out.println("比较 100 和 200: " + int1.compareTo(int2)); // 如果小于则为-1，如果等于则为0，如果大于则为1
+
+ // equals() 方法
+ Double double1 = 123.45;
+ Double double2 = 123.45;
+ System.out.println("用 equals() 比较 123.45 和 123.45: " + double1.equals(double2));
+
+ NumberFormat nf = NumberFormat.getInstance();
+ nf.setMaximumFractionDigits(3); // 设置小数点后最多3位
+ System.out.println("格式化后:"+nf.format(131321311.1231312));
+ System.out.println("=========================Number类的用法=========================");
+ }
+}
diff --git a/src/main/java/smy/javastudy/classes/StringBufferClass.java b/src/main/java/smy/javastudy/classes/StringBufferClass.java
new file mode 100644
index 0000000..56b744c
--- /dev/null
+++ b/src/main/java/smy/javastudy/classes/StringBufferClass.java
@@ -0,0 +1,49 @@
+package smy.javastudy.classes;
+
+public class StringBufferClass {
+
+ public void StringBufferClass() {
+ System.out.println("\n=====================StringBufferClass==========================");
+ // 初始对象，后续操作不会修改此对象
+ StringBuffer original = new StringBuffer("Hello World");
+ System.out.println("初始字符串: " + original);
+
+ // 1. 追加操作 - 基于原对象创建副本后操作
+ StringBuffer appended = new StringBuffer(original); // 复制原对象
+ appended.append(" appended text.");
+ System.out.println("追加字符串: " + appended);
+
+ // 2. 插入操作 - 基于原对象创建副本后操作
+ StringBuffer inserted = new StringBuffer(original); // 复制原对象
+ inserted.insert(0, "Start-");
+ System.out.println("插入字符串: " + inserted);
+
+ // 3. 替换操作 - 基于原对象创建副本后操作
+ StringBuffer replaced = new StringBuffer(original); // 复制原对象
+ replaced.replace(1, 3, "replaced");
+ System.out.println("替换字符串: " + replaced);
+
+ // 4. 反转操作 - 基于原对象创建副本后操作
+ StringBuffer reversed = new StringBuffer(original); // 复制原对象
+ reversed.reverse();
+ System.out.println("反转字符串: " + reversed);
+
+ // 5. 删除操作 - 基于原对象创建副本后操作
+ StringBuffer deleted = new StringBuffer(original); // 复制原对象
+ deleted.delete(0, deleted.length() - 1);
+ System.out.println("删除字符串: " + deleted);
+
+ // 6. 获取长度
+ int length = original.length();
+ System.out.println("原始字符串长度: " + length);
+
+ //获取容量
+ int capacity = original.capacity();
+ System.out.println("原始字符串容量: " + capacity);
+
+ System.out.println("=====================StringBufferClass==========================\n");
+
+
+
+ }
+}
diff --git a/src/main/java/smy/javastudy/classes/StringClass.java b/src/main/java/smy/javastudy/classes/StringClass.java
new file mode 100644
index 0000000..8748d2f
--- /dev/null
+++ b/src/main/java/smy/javastudy/classes/StringClass.java
@@ -0,0 +1,117 @@
+package smy.javastudy.classes;
+
+import java.nio.charset.StandardCharsets;
+import java.util.Arrays;
+import java.util.Locale;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+public class StringClass {
+
+ //注意:String 类是不可改变的，所以你一旦创建了 String 对象，那它的值就无法改变了（详看笔记部分解析）。
+ //如果需要对字符串做很多修改，那么应该选择使用 StringBuffer & StringBuilder 类。
+
+ public void StringClass() {
+ System.out.println("\n=========================String类的用法=========================");
+
+ // 1. 创建与不可变性（immutable）
+ String str = "Hello, World!"; // 字面量（驻留在字符串池）
+ // 显式创建一个在堆上的新字符串对象（与字面量不同的引用），用于演示引用相等 vs 值相等
+ String newObj = new StringBuilder(str).toString(); // 新对象（堆），用于演示引用不相等
+ System.out.println("str == newObj ? " + (str == newObj) + " // intentional: compare references"); // false（引用不同）
+ System.out.println("str.equals(newObj) ? " + str.equals(newObj)); // true（内容相同）
+
+ // 2. 基本常用方法
+ System.out.println("字符串: " + str);
+ System.out.println("长度: " + str.length());
+ System.out.println("索引7的字符: " + str.charAt(7));// 索引从0开始 输出w 空格也算
+ System.out.println("子串(7,12): " + str.substring(7, 12)); // 包含7，不包含12
+ System.out.println("连接: " + str.concat(" Let's learn Java."));
+ System.out.println("是否包含 'World' : " + str.contains("World"));
+ System.out.println("第一次出现 'o' 的索引: " + str.indexOf('o')); // 找不到返回 -1
+ System.out.println("最后出现 'o' 的索引: " + str.lastIndexOf('o'));
+ System.out.println("替换 (World->Java): " + str.replace("World", "Java"));
+ System.out.println("大写: " + str.toUpperCase(Locale.ENGLISH));
+ System.out.println("小写: " + str.toLowerCase(Locale.ENGLISH));
+
+
+ // 3. 去空白与比较
+ String padded = " Leading and trailing spaces ";
+ System.out.println("原始: '" + padded + "'");
+ System.out.println("trim() -> '" + padded.trim() + "'"); // Java 8 起可用
+ // Java 11+: strip(), isBlank(), repeat() 等更强大，若使用低版本请注释
+ System.out.println("strip() -> '" + padded.strip() + "'");
+
+ String s1 = "Hello";
+ String s2 = "hello";
+ System.out.println("equals 忽略大小写: " + s1.equalsIgnoreCase(s2));
+ System.out.println("compareTo (字典序): " + s1.compareTo(s2)); // 区分大小写
+
+ // 4. split / join / format
+ String str2 = "Java Programming";
+ System.out.println("分割字符串（空格）:");
+ String[] parts = str2.split(" ");
+ System.out.println(Arrays.toString(parts));
+ System.out.println("join 示例: " + String.join(" | ", parts));
+
+ int number = 42;
+ double pi = 3.14159;
+ String formatted = String.format("Number: %d, Pi: %.2f", number, pi);
+ System.out.println("格式化: " + formatted);
+
+ // 5. 正则与 replaceAll / matches
+ String mixed = "abc123xyz456";
+ System.out.println("matches digits only? " + "12345".matches("\\d+")); // true
+ Pattern p = Pattern.compile("\\d+");
+ Matcher m = p.matcher(mixed);
+ System.out.print("正则查找数字: ");
+ while (m.find()) {
+ System.out.print(m.group() + " ");
+ }
+ System.out.println();
+ System.out.println("regex replace (digits->#): " + mixed.replaceAll("\\d", "#"));
+
+ // 6. split 的 limit 使用与注意事项
+ String csv = "a,b,c,d";
+ System.out.println("split limit=2: " + Arrays.toString(csv.split(",", 2))); // [a, b,c,d]
+ System.out.println("split limit=0 (默认): " + Arrays.toString(csv.split(",")));
+
+ // 7. 性能提示：大量拼接用 StringBuilder
+ StringBuilder sb = new StringBuilder(64);
+ for (int i = 0; i < 5; i++) {
+ sb.append(i).append('-');
+ }
+ String built = sb.toString();
+ System.out.println("使用 StringBuilder 拼接: " + built);
+
+ // 8. 字符编码与字节转换（注意编码）
+ String chinese = "你好，世界";
+ byte[] utf8 = chinese.getBytes(StandardCharsets.UTF_8);
+ String fromUtf8 = new String(utf8, StandardCharsets.UTF_8);
+ System.out.println("原始: " + chinese + " | bytes length(UTF-8): " + utf8.length + " | 还原: " + fromUtf8);
+
+ // 9. 与基本类型互转
+ String intStr = "123";
+ int parsed = Integer.parseInt(intStr);
+ System.out.println("解析数字: " + parsed + " (类型 int)");
+ // 演示把基本类型变成字符串的常见方式：Integer.toString 或 String.valueOf
+ System.out.println("Integer.toString(parsed) -> " + Integer.toString(parsed));
+
+ // 10. 小心常见错误与边界
+ // substring 越界会抛出 IndexOutOfBoundsException
+ // indexOf 返回 -1 要先判断再用
+ String maybe = "abc";
+ int idx = maybe.indexOf('x');
+ System.out.println("indexOf 'x' -> " + idx + " (如果 -1 就表示没找到)");
+
+ // 11. 文本块（text block）示例（Java 13+），若你的 JDK 版本低，请注释掉下面部分
+ // String multiLine = """
+ // This is a multi-line
+ // string example.
+ // It preserves line breaks and spaces.
+ // """;
+ // System.out.println("多行文本块示例: " + multiLine);
+
+ System.out.println("=========================String类的用法=========================");
+ }
+}