本书主要通过代码案例帮助读者学习Java基础部分的相关知识，大部分内容都是以代码的形式呈现的，讲解部分也融入了代码注释中。通过阅读本书，读者可以更轻松、高效地掌握Java语言的语法结构与编程思维。本书首先介绍了Java语言中的基础语法结构，比如常量、变量、流程控制、数组、方法（函数）、面向对象、封装、继承、多态、抽象、接口、异常等，还介绍了日常开发中常见的一些工具类的相关使用方法。每个知识点都配备了相应的实操案例，包括具体的使用场景。本书内容以实操案例为主，对以实操为出发点的读者会更加友好。笔者（老邪）认为，可以通过搜索引擎轻松了解的知识，比如Java语言的概念、理论、历史、定义等相关内容，没有必要在本书中占用过多的篇幅。并且笔者认为，一切没有实操结果支撑的概念、理论都过于抽象，一些专业技术名词更加难以理解。所以在本书中，笔者整理了近百个实操案例，帮助读者快速地上手Java。

王冰，笔名为IT老邪，T教培行业从业十余年，累计授课时长超过两万小时，从业期间经手学员数以万计授课内容涵盖、C/C++ 语言、嵌入式开发、JavaWeb全栈开发、Web前端开发、PHP全栈开发、以及 Python 等主流开发语言。曾获得高校毕业生就业协会颁发的双师型导师认证，也曾任多个高校的牌品专业课讲师。抖音自媒体平台中粉丝量十余万。

目　　录
第 1 章　小肆的第一个 Java 程序...........................................................1
1.1 Java 开发工具 ..................................................................................................... 1
1.1.1　编码工具 ....................................................................................1
1.1.2 IDE 集成开发工具 ....................................................................1
1.2　环境搭建 ............................................................................................................. 2
1.2.1 JVM、JRE、JDK 介绍 .............................................................2
1.2.2 JDK 的下载与安装 ....................................................................2
1.2.3 IntelliJ IDEA 的安装与使用 .....................................................5
第 2 章　常量与变量.......................................................................... 11
2.1　常量 ................................................................................................................... 11
2.2　数据类型的分类 ............................................................................................... 12
2.2.1　基本数据类型 ..........................................................................13
2.2.2　引用数据类型 ..........................................................................13
2.3　变量 ................................................................................................................... 14
2.3.1　变量的定义 ..............................................................................14
2.3.2　变量的输出 ..............................................................................15
2.3.3　使用变量的注意事项 ..............................................................17
X　|　码解Java：让初学者读懂代码的入门书
2.3.4　数据类型转换 ..........................................................................17
2.4　本章思考 ........................................................................................................... 19
第 3 章　运算符 ................................................................................ 21
3.1　运算符的分类 ................................................................................................... 21
3.1.1　算术运算符 ..............................................................................21
3.1.2　逻辑运算符 ..............................................................................22
3.1.3　关系运算符 ..............................................................................23
3.1.4　三元运算符 ..............................................................................24
3.1.5　位运算符（了解） ..................................................................24
3.1.6　赋值运算符 ..............................................................................26
3.1.7　自增 / 自减运算符 ...................................................................27
3.2　思考 ................................................................................................................... 28
3.3　运算符优先级 ................................................................................................... 28
第 4 章　流程控制之判断结构............................................................. 29
4.1　程序运行流程（顺序） ................................................................................... 29
4.2　程序运行流程（可控） ................................................................................... 29
4.3 if 判断 ................................................................................................................ 30
4.3.1 if 的单独使用 ...........................................................................30
4.3.2 if 与 else 的配合使用 ..............................................................32
4.3.3 else if 的使用 ...........................................................................33
4.4.4 if 的嵌套使用 ...........................................................................38
4.4　思考 ................................................................................................................... 38
4.4.1　判断奇数 / 偶数 .......................................................................39
4.4.2　判断平闰年 ..............................................................................39
第 5 章　流程控制之分支 ................................................................... 40
5.1　标准语法 ........................................................................................................... 40
5.2　语法规则 ........................................................................................................... 41
5.3　案例 ................................................................................................................... 42
目　　录　　|　XI
5.3.1　成绩等级划分 ..........................................................................42
5.3.2　使用键盘进行输入 ..................................................................43
5.3.3　计算器的基本功能 ..................................................................44
5.3.4　用户输入一个年份和月份，输出其对应的天数 ..................45
5.3.5　恺撒日期 ..................................................................................46
第 6 章　流程控制之循环 ................................................................... 49
6.1　循环的种类及标准写法 ................................................................................... 49
6.1.1 while 循环 ................................................................................49
6.1.2 do while 循环 ...........................................................................50
6.1.3 for 循环 ....................................................................................51
6.2 break 和 continue ............................................................................................... 52
6.2.1 break 的用法 ............................................................................52
6.2.2 continue 的用法 .......................................................................54
6.3　案例 ................................................................................................................... 55
6.3.1　输出 1-10 ..................................................................................55
6.3.2　输出 1 ～ 100 累加和 ..............................................................55
6.3.3　输出 1 ～ 100 的偶数和 ..........................................................56
6.3.4　输出所有水仙花数 ..................................................................56
6.3.5　输出 9 行 9 列星号组成的矩形 ..............................................57
6.3.6　输出 9 行星号组成的直角三角形 ..........................................57
6.3.7　九九乘法表 ..............................................................................58
6.3.8　输出 7 行 * 号组成的等腰三角形 ..........................................59
6.3.9　输出 1000 以内的素数 ............................................................60
第 7 章　数组 ................................................................................... 61
7.1　数组的概念 ....................................................................................................... 61
7.2　数组的使用 ....................................................................................................... 61
7.2.1　数组的定义 ..............................................................................61
7.2.2　数组的初始化 ..........................................................................62
7.2.3　数组成员的访问 ......................................................................62
XII　|　码解Java：让初学者读懂代码的入门书
7.2.4　数组的特性 ..............................................................................62
7.3　案例 ................................................................................................................... 63
7.3.1　数组的遍历 ..............................................................................63
7.3.2　求最值 ......................................................................................63
7.3.3　查找数组中指定元素的所在位置 ..........................................64
7.3.4　数组逆序存储 ..........................................................................65
7.3.5　向有序数组中插入元素后保证数组仍有序 ..........................66
7.3.6　数组元素排序（升序、降序）——冒泡法 ..........................68
7.3.7　二维数组——矩阵转置（了解即可） ..................................70
7.3.8　二维数组——杨辉三角（了解即可） ..................................72
第 8 章　方法（函数）....................................................................... 74
8.1　方法的概念 ....................................................................................................... 74
8.1.1　方法的用途 ..............................................................................74
8.1.2　名词解析 ..................................................................................74
8.1.3　使用方法时的注意事项 ..........................................................75
8.1.4　方法的定义 ..............................................................................75
8.1.5　方法示例 ..................................................................................75
8.2　案例 ................................................................................................................... 78
8.3　方法的重载 ....................................................................................................... 80
8.3.1　方法的重载的特点 ..................................................................80
8.3.2　案例 ..........................................................................................81
第 9 章　面向对象............................................................................. 82
9.1　面向对象中类与对象的概念 ........................................................................... 82
9.2　类的定义 ........................................................................................................... 83
9.3　对象的使用 ....................................................................................................... 83
9.3.1　对象的使用步骤 ......................................................................83
9.3.2　成员变量与局部变量 ..............................................................85
9.3.3　成员方法与普通方法 ..............................................................85
9.3.4　对象间的赋值 ..........................................................................86
目　　录　　|　XIII
9.3.5　方法中对象的使用 ..................................................................86
9.3.6 this 的用法 ...............................................................................87
9.4　封装 ................................................................................................................... 87
9.5　构造方法 ........................................................................................................... 89
9.6　案例 ................................................................................................................... 90
第 10 章　继承.................................................................................. 94
10.1　继承的作用（意义） ..................................................................................... 94
10.2　继承的特点 ..................................................................................................... 94
10.3　继承的格式 ..................................................................................................... 95
10.4　继承间成员的访问 ......................................................................................... 95
10.4.1　父类、子类、局部变量名重复、冲突时访问规则 ............95
10.4.2　方法名重复时的访问规则——方法的重写 ........................96
10.5　继承中的权限 ................................................................................................. 98
第 11 章　抽象和接口 ........................................................................ 99
11.1　抽象（abstract） ............................................................................................. 99
11.1.1 abstract 修饰符 .......................................................................99
11.1.2　举例说明 ................................................................................99
11.1.3　案例 ......................................................................................100
11.2　接口（interface） .......................................................................................... 101
11.2.1　接口的定义 ..........................................................................102
11.2.2　接口中的成员 ......................................................................102
11.3　接口的实现 .................................................................................................... 103
11.3.1　实现接口的格式 ..................................................................103
11.3.2　一个类可以同时实现多个接口 ..........................................103
11.3.3　接口的多继承 ......................................................................104
11.3.4　一个类可以在继承其他类的同时实现一个或多个接口 ...104
11.4 final 的使用.................................................................................................... 104
11.5　案例 ................................................................................................................ 105
11.5.1 Demo01 ................................................................................105
XIV　|　码解Java：让初学者读懂代码的入门书
11.5.2 Demo02 ................................................................................109
11.5.3 Demo03 ................................................................................ 110
第 12 章　多态................................................................................ 113
12.1　格式 ............................................................................................................... 113
12.2　多态调用成员方法 ....................................................................................... 113
12.3　多态调用成员属性 ....................................................................................... 114
12.4　对象的上下转型 ........................................................................................... 114
12.5　案例 ............................................................................................................... 114
12.5.1　动物案例 .............................................................................. 114
12.5.2 USB 设备实例 ..................................................................... 117
第 13 章　内部类............................................................................. 120
13.1　内部类的概述 ............................................................................................... 120
13.1.1　内部类的定义格式 ..............................................................120
13.1.2　内部类的访问特点 ..............................................................120
13.2　内部类的分类 ............................................................................................... 121
13.2.1　成员内部类 ..........................................................................121
13.2.2　局部内部类 ..........................................................................122
13.2.3　匿名内部类 ..........................................................................123
第 14 章　常用类............................................................................. 127
14.1　包装类 ........................................................................................................... 127
14.2 String .............................................................................................................. 130
14.2.1　字符串类的特点 ..................................................................130
14.2.2　常用构造方法 ......................................................................130
14.2.3 String 对象的特点 ...............................................................131
14.2.4 String 的比较 .......................................................................131
14.2.5　常用方法 ..............................................................................132
14.2.6　示例 ......................................................................................133
14.3 StringBuilder ＆ StringBuffer ........................................................................ 137
目　　录　　|　XV
14.4 String 和 StringBuilder 的相互转换 ............................................................. 139
14.5 Arrays ............................................................................................................. 139
14.6 Math ............................................................................................................... 141
14.7 Object ............................................................................................................. 142
14.8 System ............................................................................................................ 146
14.9 Date ................................................................................................................ 147
14.10 SimpleDateFormat ....................................................................................... 148
14.11 Calendar ....................................................................................................... 150
14.11.1　获取对象 ............................................................................150
14.11.2　常用方法 ............................................................................150
第 15 章　File ................................................................................. 152
15.1　构造方法 ....................................................................................................... 152
15.2 File 类的创建功能 ........................................................................................ 153
15.3 File 类的判断和获取功能 ............................................................................ 153
15.4 File 类的删除功能 ........................................................................................ 154
15.5　递归遍历目录 ............................................................................................... 155
第 16 章　I/O 流............................................................................. 157
16.1 I/O 流的分类 ................................................................................................. 157
16.2　字节流 ........................................................................................................... 158
16.2.1　字节流写数据 ......................................................................158
16.2.2　字节流输出异常处理 ..........................................................160
16.2.3　字节流读数据 ......................................................................160
16.2.4　字节输入 / 输出流缓冲区 ...................................................163
16.3　字符流 ........................................................................................................... 166
16.3.1　字符流写数据 —— write() .................................................168
16.3.2　字符流读数据—— read() ...................................................169
16.3.3　复制文件 ..............................................................................170
16.3.4　缓冲区（高效读写） ..........................................................171
16.4　标准输入流和标准输出流 ........................................................................... 173
XVI　|　码解Java：让初学者读懂代码的入门书
第 17 章　序列化............................................................................. 174
17.1　对象序列化 ................................................................................................... 174
17.2　对象序列化流 ............................................................................................... 174
17.3　对象反序列化流 ........................................................................................... 175
17.4　案例（读写） ............................................................................................... 175
17.5　序列化过程中的问题 ................................................................................... 177
第 18 章　异常................................................................................ 178
18.1　异常处理方式 ............................................................................................... 178
18.2　异常类 ........................................................................................................... 178
18.3　异常的解决方案 ........................................................................................... 179
18.4　异常的抛出 ................................................................................................... 180
18.5　自定义异常类 ............................................................................................... 181
第 19 章　Java 中的集合................................................................... 184
19.1　集合概述 ....................................................................................................... 184
19.2 ArrayList ........................................................................................................ 184
19.2.1 ArrayList 构造方法和添加方法 .........................................185
19.2.2 ArrayList 集合中的常用方法 .............................................185
19.3 Collection ....................................................................................................... 201
19.3.1 Collection 集合概述 ............................................................201
19.3.2 Collection 集合常用方法 ....................................................202
19.3.3 Collection 集合的遍历 ........................................................202
19.4 List ................................................................................................................. 203
19.4.1 List 集合概述 .......................................................................203
19.4.2 List 集合特有方法 ...............................................................204
19.4.3 List 集合的遍历 ...................................................................204
19.4.4　并发修改异常 ......................................................................205
19.4.5 ListIterator ............................................................................206
19.4.6　数据结构 ..............................................................................208
19.4.7 List 集合子类 .......................................................................212
目　　录　　|　XVII
19.4.8 LinkedList ............................................................................213
19.5 Set .................................................................................................................. 214
19.5.1 Set 集合概述 ........................................................................214
19.5.2 Hash 值 .................................................................................215
19.5.3 Hash 表 .................................................................................217
19.5.4 HashSet .................................................................................217
19.5.5 LinkedHashSet .....................................................................218
19.5.6 TreeSet ..................................................................................219
19.6　泛型 ............................................................................................................... 224
19.6.1　泛型定义格式 ......................................................................224
19.6.2　泛型的优点 ..........................................................................224
19.6.3　泛型类 ..................................................................................225
19.6.4　泛型方法 ..............................................................................227
19.6.5　泛型接口 ..............................................................................229
19.6.6　泛型通配符 ..........................................................................230
19.6.7　可变参数 ..............................................................................231
19.6.8　可变参数的使用 ..................................................................232
19.7 Map ................................................................................................................ 233
19.7.1 Map 集合概述和使用 ..........................................................233
19.7.2 Map 集合的常用方法 ..........................................................234
19.7.3 Map 集合的获取功能 ..........................................................236
19.7.4 Map 集合的遍历 ..................................................................237
19.7.5　集合嵌套 ..............................................................................239
19.7.6 Map 集合案例 ......................................................................240
19.7.7 Collections ............................................................................241
19.8 Properties ....................................................................................................... 244
第 20 章　Java 中的反射................................................................... 247
20.1　类加载器（了解） ....................................................................................... 247
20.1.1　类加载 ..................................................................................247
20.1.2　类加载器 ..............................................................................248
20.2　反射 ............................................................................................................... 249
XVIII　|　码解Java：让初学者读懂代码的入门书
20.2.1　概述 ......................................................................................249
20.2.2　获取 Class 类的对象 ...........................................................250
20.2.3　通过反射获取构造方法 ......................................................250
20.2.4　通过反射创建对象 ..............................................................251
20.2.5　反射获取成员变量 ..............................................................252
20.2.6　反射获取成员方法 ..............................................................253
20.2.7　反射抑制泛型检查 ..............................................................254
20.2.8　通过配置文件实现反射 ......................................................255
第 21 章　Java 中的多线程................................................................ 258
21.1　实现多线程 ................................................................................................... 258
21.1.1　多线程的实现：方式一 ......................................................258
21.1.2　设置和获取线程名称 ..........................................................259
21.1.3　线程调度 ..............................................................................260
21.1.4　线程控制 ..............................................................................261
21.1.5　线程生命周期 ......................................................................265
21.1.6　多线程的实现：方式二 ......................................................265
21.2　线程同步 ....................................................................................................... 267
21.2.1　线程同步概述 ......................................................................267
21.2.2　线程同步的优势与弊端 ......................................................270
21.2.3　线程同步方法 ......................................................................270
21.2.4　线程安全的类 ......................................................................272
21.2.5 Lock ......................................................................................273
21.3　生产者、消费者模型 ................................................................................... 274
21.4 Timer 定时器 ................................................................................................. 277
第 22 章　Lambda 表达式 ................................................................ 279
22.1 Lambda 概述 ................................................................................................. 279
22.1.1　简单案例：通过 Lambda 创建并启动线程 .......................279
22.1.2 Lambda 表达式的基本格式 ................................................280
22.1.3 Lambda 表达式案例 ............................................................280
目　　录　　|　XIX
22.1.4 Lambda 的省略模式 ............................................................281
22.1.5 Lambda 的注意事项 ............................................................284
22.1.6 Lambda 与匿名内部类 ........................................................284
22.2 Lambda 支持的方法引用 ............................................................................. 284
22.1.1　常见的引用方式 ..................................................................284
22.1.2　案例 ......................................................................................284
22.3　函数式接口 ................................................................................................... 290
22.3.1　函数式接口作为方法的参数 ..............................................291
22.3.2　函数式接口作为方法的返回值 ..........................................291
22.4　常用的函数式接口 ....................................................................................... 292
22.4.1 Supplier ................................................................................292
22.4.2 Consumer ..............................................................................294
22.4.3 Predicate ...............................................................................295
22.4.4 Function ................................................................................297
22.5 Stream 流 ....................................................................................................... 298
22.5.1　流的不同状态 ......................................................................298
22.5.2 Stream 流的生成方式 ..........................................................299
22.5.3 Stream 中间流的操作方式 ..................................................300
22.5.4 Stream 结束流的操作方式 ..................................................303
22.5.5　案例 ......................................................................................304
第 23 章　网络编程 ......................................................................... 306
23.1　网络编程概述 ............................................................................................... 306
23.2 UDP 通信程序 .............................................................................................. 308
23.2.1 UDP 通信原理 .....................................................................308
23.2.2　使用 UDP 发送数据 ............................................................309
23.2.3　使用 UDP 接收数据 ............................................................310
23.2.4　案例：使用 UDP 收 / 发数据 ............................................. 311
23.2.5　模拟聊天室 ..........................................................................313
23.3 TCP 通信程序 ............................................................................................... 319
23.3.1 TCP 通信原理 ......................................................................319
23.3.2　使用 TCP 发送数据 .............................................................319
XX　|　码解Java：让初学者读懂代码的入门书
23.3.3　使用 TCP 接收数据 .............................................................320
23.3.4　案例 ......................................................................................320
第 24 章　Java 中的枚举类型 ............................................................ 329
24.1　枚举类型的概述 ........................................................................................... 329
24.2　语法结构 ....................................................................................................... 329
24.2.1　基本语法结构示例 ..............................................................329
24.2.2　完整语法结构示例 ..............................................................330
24.2.3　枚举的 set 方法与 get 方法 .................................................332
24.2.4　枚举的常用方法 ..................................................................333
24.3　应用场景 ....................................................................................................... 333
24.4　注意事项 ....................................................................................................... 335