java体系总结

【核心代码】

目录
一 java 基础...................................................................................................................................17
1.1java 的 8 种基本数据类型 装箱 拆箱........................................................................17
1.1.1．8 种基本数据类型..........................................................................................17
1.1.2．装箱和拆箱...................................................................................................... 18
1.1.3．String 转出 int 型，判断能不能转？如何转？...................................... 18
1.1.4 short s1 = 1; s1 = s1   1;有什么错? short s1 = 1; s1  =1;有什么
错?
...................................................................................................................................19
1.1.5．Int 与 Integer 区别.......................................................................................19
1.1.6．字节字符区别..................................................................................................20
1.1.7 java 基本类型与引用类型的区别...................................................................20
1.2 重写重载封装继承多态.................................................................................................20
1.3 Stack Queue
............................................................................................................... 21
1.3.1 PriorityQueue
................................................................................................ 21
1.7 Concurrent 包.............................................................................................................26
1.8 面向对象......................................................................................................................... 27
1.9 String StringBuffer StringBuilder hashcode equal
.................................... 27
String 中的 hashcode 以及 toString
...........................................................................28
1.10 java 文件读取........................................................................................................... 29
1.11 Java 反射................................................................................................................... 30
1.12 JDK NDK JRE JNI
................................................................................................31
1.13 static 和 final 的区别..............................................................................................31
1.14 map，list，set 区别................................................................................................33
1.16 Session 和 COOKIE
................................................................................................. 34
1.19 IO NIO BIO AIO select epoll
............................................................................35
1.19.1 NIO 的原理.....................................................................................................36
1.20 ThreadLocal
.............................................................................................................38
1.22 finalize finalization finally
..................................................................................38
1.23 public private default protected
.....................................................................39
1.25 Object
.........................................................................................................................39
1.26 equls 和 == 的区别.................................................................................................40
1.27 异常............................................................................................................................. 40
1.28 序列化......................................................................................................................... 42
1.30 comparable 接口和 comparator 接口...............................................................44
1.33 接口和抽象类............................................................................................................. 45
1.34 Socket
.........................................................................................................................47
1.35 Runtime 类.................................................................................................................... 47
1.36 值传递与引用传递.....................................................................................................47
1.37 泛型 ？与 T 的区别.................................................................................................. 47
1.38 枚举类型字节码层面理解 Enum............................................................................... 48
1.39 java 注解类型.......................................................................................................... 50
1.40 字节流 字符流........................................................................................................... 50
1.41 静态内部类 匿名类...................................................................................................52
1.41.2 匿名类...............................................................................................................54
二．集合类 Set
..............................................................................................................................56
2.1 HashMap
......................................................................................................................56
(1) hashMap 的原理..................................................................................................... 56
（3） get
....................................................................................................................... 58
（4）HashMap 的 put 方法源码.................................................................................58
（5）HashMap 问题 jdk1.8 优化...............................................................................59
7.Hashmap 中的 key 可以为任意对象或数据类型吗？......................................... 60
2.2 CurrentHashMap
......................................................................................................61
0. JDK1.7 ConCurrentHashMap 原理.......................................................................61
1. JDK1.7 Get
........................................................................................................... 62
2. JDK1.7 PUT
.............................................................................................................. 64
3. JDK1.7 Remove
...................................................................................................66
4.JDK1.7 & JDK1.8 size()
................................................................................... 67
5.JDK 1.8....................................................................................................................67
6.JDK1.8 put
..................................................................................................................68
7. JDK1.8 get 方法...................................................................................................70
8. rehash 过程............................................................................................................. 70
2.3 . Hashtable
.................................................................................................................. 70
0.参数..............................................................................................................................70
1.put
................................................................................................................................ 71
2.get
................................................................................................................................ 71
3.Remove
.......................................................................................................................72
4.扩容............................................................................................................................. 72
2.4 hashtable 和 hashmap 的区别................................................................................ 73
2.5 HashMap 和 ConCurrentHashMap 区别..........................................................73
2.6 ConcurrentHashMap 和 HashTable 区别........................................................... 73
2.7 linkedHashMap
....................................................................................................... 74
2.8 Linkedhashmap 与 hashmap 的区别.................................................................. 74
2.9 HashSet
........................................................................................................................ 75
2.10 hashmap 与 hashset 区别......................................................................................76
2.11 Collections.sort 内部原理..................................................................................... 76
2.12 hash 算法....................................................................................................................77
2.13 迭代器 Iterator Enumeration
........................................................................... 78
2.14 LIST ArrayList，LinkedList 和 Vector 的区别和实现原理........................79
2.15 快速失败(fail-fast)和安全失败(fail-safe)
...................................................................80
三 锁 volatile synchronized Lock ReentrantLock AQS CAS
....................................81
3.1 .volatile 和 synchronized
.......................................................................................81
3.1.1 Volatile 与 synchronized 区别................................................................. 84
3.1.2 Volatile
..............................................................................................................84
3.1.3 Synchronized 原理........................................................................................ 84
3.2 CAS
..............................................................................................................................87
3.3 可重入锁 ReentrantLock
......................................................................................... 87
1.5.3 乐观锁和悲观锁 阻塞锁，自旋锁，偏向锁，轻量锁，重量锁。公平锁 非公
平锁................................................................................................................................. 88
3.3 ReentrantLock 和 synchronized 区别.............................................................. 88
1.5.3 重入锁、对象锁、类锁的关系........................................................................89
四 java 多线程；..........................................................................................................................89
4.1 ．如何创建线程？哪种好？........................................................................................90
4.2．线程状态...................................................................................................................... 90
4.3．一般线程和守护线程的区别......................................................................................91
4.4．sleep wait yield notify notifyAll join
.......................................................... 91
4.5 中断线程......................................................................................................................... 92
4.6 多线程如何避免死锁....................................................................................................93
4,7 多线程的好处以及问题................................................................................................94
4.8 多线程共用一个数据变量注意什么？........................................................................94
4.9 线程通信方式................................................................................................................ 94
4.10 线程池......................................................................................................................... 95
4.11.线程中抛出异常怎么办..............................................................................................95
五．Java 进阶 ssh/ssm 框架.....................................................................................................97
2.1Spring
.............................................................................................................................97
2.1.0 什么是 Spring 以及优点................................................................................... 97
2.1.1 ApplicationContext 和 beanfactory 的区别................................................... 97
2.1.2 Spring Bean 生命周期........................................................................................98
2.1.3 spring 中 bean 的作用域............................................................................... 98
2.1.4 Spring IOC.......................................................................................................99
2.1.5 Spring AOP..........................................................................................................99
2.1.6 事务................................................................................................................. 101
2.1.7 Spring MVC...................................................................................................103
2.1.8 Spring 中设计模式........................................................................................104
2.2 Servlet
........................................................................................................................105
2.2.1 Servlet 生命周期............................................................................................. 105
2.2 Struts
.............................................................................................................................106
2.2.1 Struts 工作流程................................................................................................ 106
2.2.2 Struts 工作原理...........................................................................................106
2.2.3 do Fliter
........................................................................................................ 107
2.2.4 拦截器与过滤器的区别.................................................................................108
2.2.5 Struts 中为什么不用考虑线程安全............................................................108
2.2.6 Struts2 和 Struts1 区别........................................................................ 108
2.3 Hibernate
..................................................................................................................109
2.4 Redis
........................................................................................................................... 109
2.5 Tomcat
...................................................................................................................... 109
2.6 netty
...........................................................................................................................110
2.7 Hadoop
...................................................................................................................... 110
2.8 Volley
..........................................................................................................................110
六．Java 内存模型 和 垃圾回收...........................................................................................111
3.0 什么是 JMM 内存模型？（JMM 和内存区域划分不是一回事）...................... 111
3.0.1 JMM 中的 happens-before 原则....................................................................111
3.1 内存分区..................................................................................................................... 113
3.2 GC 算法（YGC and FGC）...................................................................................115
3.2.1 YGC.................................................................................................................116
3.2.2 FGC....................................................................................................................116
3.3 垃圾收集器 CMS
......................................................................................................116
3.4 java 类加载机制 双亲委派...................................................................................... 117
3.4.1 java 类加载的过程........................................................................................... 117
3.4.2 双亲委派机制...................................................................................................119
3.4.3 破坏双亲委派模型.........................................................................................120
3.5 内存泄露..................................................................................................................... 121
3.6 .内存泄露的案例分析 jvm 调优..............................................................................121
3.6.1 jvm 调优目的.................................................................................................121
3.6.2 案例分析......................................................................................................... 122
3.7 jstat jmap jps jinfo jconsole
..............................................................................125
3.7.1 jstat
.................................................................................................................125
3.7.2 jmap
............................................................................................................... 126
3.7 JVM 参数设置.......................................................................................................... 126
3.8 内存分配与回收策略.................................................................................................128
3.9 面试问题..................................................................................................................... 129
3.9.1 一般 Java 堆是如何实现的？.......................................................................129
3.9.2 对象在内存中的初始化过程.........................................................................129
3.9.3 对象的强、软、弱和虚引用...........................................................................129
3.9.4 如何减少 GC 的次数..................................................................................... 130
3.9.5 新生代 老年代 永久代............................................................................... 131
七． juc 包..................................................................................................................................132
7.0 juc 概况......................................................................................................................... 132
7.1 Tools
............................................................................................................................133
7.1.1 CountDownLatch
.......................................................................................133
7.1.2 CyclicBarrier
..................................................................................................... 133
7.1.3 Semaphore
....................................................................................................... 133
7.1.4 Exchanger
.........................................................................................................134
7.2 List Set
.......................................................................................................................... 134
7.3 Map
........................................................................................................................... 134
7.4 Queue
.......................................................................................................................134
7.4.1 ArrayBlockingQueue
....................................................................................... 134
7.4.2 LinkedBlockingQueue
.....................................................................................135
7.4.3 LinkedBlockingQueue 和 ArrayBlockingQueue 迥异...............................135
7.5 线程池...........................................................................................................................136
1.线程池工作原理.......................................................................................................136
2.线程池分类...............................................................................................................136
3.线程池底层实现类 ThreadPoolExecutor 类........................................................136
4.线程池状态...............................................................................................................137
四.设计模式................................................................................................................................. 138
4.0 什么是设计模式......................................................................................................... 138
4.1.常见的设计模式及其 JDK 中案例：....................................................................... 138
4.1.1 适配器模式..................................................................................................... 138
4.1.2 迭代器模式..................................................................................................... 138
4.1.3 代理模式.........................................................................................................138
4.1.4 观察者模式.....................................................................................................139
4.1.5 装饰器模式.....................................................................................................140
4.1.6 工厂模式.........................................................................................................141
4.1.7 建造者模式.....................................................................................................141
4.1.8 命令模式.........................................................................................................142
4.1.9 责任链模式..................................................................................................... 142
4.1.10 享元模式.......................................................................................................142
4.1.11 中介者模式...................................................................................................143
4.1.12 备忘录模式...................................................................................................143
4.1.13 组合模式.......................................................................................................143
4.1.14 模板方法模式...............................................................................................143
4.1.15 单例模式...............................................................................................................144
1.非线程安全懒汉模式............................................................................................. 144
2、 线程安全懒汉模式..............................................................................................144
3.饿汉模式..................................................................................................................144
4. 静态类内部加载.................................................................................................... 145
5.双重锁校验模式.......................................................................................................145
7. 懒汉模式与饿汉模式区别.................................................................................... 146
8. 双重校验锁方法与线程安全的懒汉模式区别.................................................... 146
4.2 设计模式六大原则..................................................................................................... 146
4.3 java 动态代理........................................................................................................... 147
算法.............................................................................................................................................. 151
海量数据...................................................................................................................................... 155
七．数据结构与算法..................................................................................................................156
7.1 排序................................................................................................................................156
7.1.1 直接插入排序................................................................................................. 157
7.1.2 希尔排序......................................................................................................... 158
7.1.3 冒泡排序......................................................................................................... 159
7.1.4 快速排序......................................................................................................... 159
7.1.5 直接选择排序................................................................................................. 162
7.1.6 堆排序............................................................................................................. 163
7.1.7 归并排序......................................................................................................... 163
7.1.8 基数排序......................................................................................................... 166
7.2 树................................................................................................................................. 167
7.2.1 二分查找树...................................................................................................... 167
八.数据库..................................................................................................................................... 172
8.1 索引 B 树 B 树..........................................................................................................172
8.1.1 索引特点优缺点适用场合.............................................................................172
8.1.2 Mysql 索引原理 B 树：...............................................................................174
8.1.3 索引分类......................................................................................................... 177
8.2 innoDB 与 MyISAM 引擎区别...............................................................................181
8.3 事务隔离级别（恶果：脏读 幻读 不可重复读）.................................................182
8.4 数据库特性 ACID.....................................................................................................183
8.5 sql
.................................................................................................................................184
8.5.1．Sql 优化........................................................................................................ 184
8.6 5 种连接 left join、right join、inner join，full join cross join
...............187
8.7 数据库范式................................................................................................................. 190
8.8 数据库连接池............................................................................................................. 190
8.8.1 数据库连接池原理...........................................................................................190
8.8.2 数据库连接池的示例代码...............................................................................191
8.9 DDL DML DCL
....................................................................................................... 192
8.10 explain
.........................................................................................................................192
8.11 分库分表.....................................................................................................................194
8.12 数据库锁.................................................................................................................. 198
8.12.1 封锁.............................................................................................................. 198
8.12.2 封锁协议（解决脏读不可重复读）..........................................................198
8.12.3 死锁活锁...................................................................................................... 199
8.12.3 解决死锁的方法.......................................................................................... 200
8.12.4 两段锁协议.................................................................................................. 202
8.12.5 GAP 锁（解决幻读）................................................................................ 203
8.12.6 next-key 锁.............................................................................................. 204
8.13 其它问题.................................................................................................................. 204
8.13.1 limit20000 如何优化............................................................................ 204
8.13.2 数据库的隔离级别 隔离级别如何实现....................................................205
8.13.3 char varchar text 区别..................................................................................205
8.13.4 drop delete truncate 区别.............................................................................206
8.13.5 事务.................................................................................................................206
8.13.6 超键、候选键、主键、外键 视图.............................................................. 206
8.13.7 存储过程与触发器.........................................................................................206
九.网络......................................................................................................................................... 209
9.1.HTTP...........................................................................................................................209
9.1.1 http 请求报文 & http 响应报文.............................................................. 209
9.1.2 http 报文头部请求头和响应头................................................................... 209
9.1.3 http 请求方法...............................................................................................210
9.1.4 http 请求过程................................................................................................210
9.1.4 Get 和 Post 区别........................................................................................211
9.1.5 http 状态码....................................................................................................212
9.1.6 http 长连接 短连接 HTTP 协议是无状态.................................................214
9.1.7 http1.1 与 http1.0 的区别............................................................................... 215
9.1.8 http2.0 与 http1.0 的区别............................................................................. 215
9.1.9 转发与重定向的区别..................................................................................... 215
9.2.TCP UDP................................................................................................................... 216
9.2.0 TCP 头部........................................................................................................ 216
9.2.1 TCP 与 UDP 区别.........................................................................................218
9.2.2 TCP 三次握手................................................................................................ 220
9.2.3 TCP 四次挥手................................................................................................ 221
9.2.4 tcp 粘包问题 nagle 算法............................................................................ 222
9.2.5 tcp 如何保证可靠性传输.............................................................................223
9.2.6 TCP 流量控制 拥塞控制..............................................................................224
9.2.7 滑动窗口机制................................................................................................. 227
9.2.8 TCP 状态转移............................................................................................... 228
9.2.9 TIME_WAIT 和 CLOSE_WAIT
............................................................... 230
9.7.计算机网络分层模型..................................................................................................232
9.7.1 osi 七层............................................................................................................232
9.7.2 APR.................................................................................................................234
9.7.3 ICMP 协议.....................................................................................................234
9.7.4 DNCP 协议........................................................................................................234
9.7.5 RARP 协议........................................................................................................235
9.7.6 路由选择协议 OSPF RIP............................................................................... 235
9.7.7 SNMP................................................................................................................ 236
9.7.8 SMTP.................................................................................................................236
9.9 IP..................................................................................................................................236
1.IP 报文.....................................................................................................................236
2. IP 地址类别........................................................................................................... 237
3. 特殊的地址............................................................................................................237
4. 私有地址................................................................................................................237
9.10 网络攻击.................................................................................................................. 238
1.SYN Flood 攻击.................................................................................................... 238
2. DDOS 攻击.............................................................................................................238
3.DNS 欺骗................................................................................................................. 238
4. 重放攻击.................................................................................................................238
5.SQL 注入..................................................................................................................238
9.11 DNS 浏览器中输入 URL 到页面加载的发生了什么........................................ 239
CDN.............................................................................................................................240
9.12 https ssl
..................................................................................................................241
9.12.1 什么是 https
...............................................................................................241
9.12.2 https 与 http 区别........................................................................................... 241
9.12.3 https 的通信过程............................................................................................242
9.12.4 SSL 工作原理..............................................................................................243
十 操作系统................................................................................................................................ 245
10.1 进程线程................................................................................................................... 245
10.1.1．进程线程区别............................................................................................ 245
10.1.2 进程通信方式.............................................................................................. 246
10.1.3 僵尸进程...................................................................................................... 246
10.1.4 进程同步 PV 信号量................................................................................... 246
10.2 死锁.......................................................................................................................... 248
10.2.1 死锁避免-银行家算法............................................................................... 248
10.2.2 死锁避免-安全序列....................................................................................249
10.3 同步 异步 阻塞 非阻塞........................................................................................249
10.4 操作系统 CPU 调度算法....................................................................................... 250
10.5 内存管理方式（页存储 段存储 段页存储）........................................................251
10.6 页面置换算法............................................................................................................253
10.6.1 概念.................................................................................................................253
10.6.2 OPT 最优页面置换算法............................................................................ 253
10.6.3 先进先出置换算法（FIFO）....................................................................... 253
10.6.4 最近最久未使用（LRU）算法.................................................................... 253
10.7 IO 种类 IO 的原理.....................................................................................................254
1. IO 种类.................................................................................................................... 255
2.设备 I/0 输入输出控制方式...................................................................................255
10.8 进程打开同一个文件 那么这两个进程得到的文件描述符（fd）相同..............256
10.9 select epoll
............................................................................................................ 256
10.10 物理地址 虚拟地址 逻辑地址..............................................................................258
十一 Linux 命令........................................................................................................................ 260
10.1 Vim...........................................................................................................................260
10.2 linux 如何查看端口被哪个进程占用？................................................................ 261
10.3 查看进程打开了哪些文件.......................................................................................262
10.4 top
................................................................................................................................262
10.5 查看 cpu 核的个数主频............................................................................................262
10.6 Linux 如何创建守护进程.......................................................................................... 262
10.7 Linux 管道机制原理..................................................................................................263
10.8 查看进程下的线程.................................................................................................... 263
10.9 linux 锁........................................................................................................................263
10.10 查看行数指令（比如第 100 行到第 150 行 top IP）........................................264
10.11 linux 进程调度.....................................................................................................265
10.14 系统调用与库函数的区别...................................................................................266
10.15 free
........................................................................................................................ 267
10.16 cache 和 buffer 的区别：....................................................................................267
10.13 其它的小问题....................................................................................................... 268
十一． 安全加密........................................................................................................................ 269
11.1 数字签名......................................................................................................................269
11.2 数字证书.....................................................................................................................270
11.3 公私钥...................................................................................................................... 270
11.4 非对称加密 RSA.................................................................................................... 271
11.5 对称密钥 DES.......................................................................................................... 271
11.6 DH 加密算法...............................................................................................................271
11.7 SHA MD5
....................................................................................................................271
十二． 代码................................................................................................................................ 272
12.1 读写文件(BufferedReader)
..................................................................................... 272
12.2 反射...........................................................................................................................273
12.3 LRU
...........................................................................................................................276
十三． 面经................................................................................................................................ 276
十四． 项目................................................................................................................................ 277
14.1. jieba 分词原理....................................................................................................... 277
Python
........................................................................................................................................279
Git
................................................................................................................................................ 279
计算机磁盘.................................................................................................................................. 279
Socket
.........................................................................................................................................279
其它.............................................................................................................................................. 279 一