Java基础9-死锁;String;编码

昨日内容回顾

死锁案例

 class DeadLock{
     public static void main(String[] args){
         Pool pool = new Pool();
         Producer p1 = new Producer("p1",pool);
         Consumer c1 = new Consumer("c1",pool);
         Consumer c2 = new Consumer("c2",pool);
         p1.setName("p1");
         c1.setName("c1");
         c2.setName("c2");

         p1.start();
         c1.start();
         c2.start();
     }
 }

 class Producer extends Thread{
     String name;
     Pool pool;
     public Producer(String name, Pool pool){
         this.name = name;
         this.pool = pool;
     }

     public void run(){
         while(true){
             pool.add();
         }
     }
 }

 class Consumer extends Thread{
     String name;
     Pool pool;
     public Consumer(String name, Pool pool){
         this.name = name;
         this.pool = pool;
     }
     public void run(){
         while(true){
             pool.remove();
         }
     }
 }

 class Pool{
     private int MAX=1;
     private int count;
     public synchronized void add(){
         String name = Thread.currentThread().getName();
         while(count>=MAX){
             try{
                 System.out.println(name+":"+"wait()");
                 this.wait();
             }
             catch(Exception e){}
         }
         System.out.println(name+":"+(++count));
         System.out.println(name+":"+"notify()");
         this.notify();
     }

     public synchronized void remove(){
         String name = Thread.currentThread().getName();
         while(count<MAX){
             try{
                 System.out.println(name+":"+"wait()");
                 this.wait();
             }
             catch(Exception e){}
         }
         System.out.println(name+":"+(--count));
         System.out.println(name+":"+"notify()");
         this.notify();
     }
 }

同步方法中，wait()与notify()执行流程

 class WaitDemo{
     public static void main(String[] args){
         Cave cave = new Cave();
         Car c1 = new Car("奔驰",cave);
         Car c2 = new Car("宝马",cave);
         c1.start();
         c2.start();

         try{
             Thread.sleep(5000);
             synchronized(cave){
                 cave.notifyAll();
             }
         }
         catch(Exception e){}
     }
 }

 class Cave{
 }
 class Car extends Thread{
     private String name;
     private Cave cave;
     public Car(String name, Cave cave){
         this.name = name;
         this.cave = cave;
     }

     public void run(){
         synchronized(cave){
             System.out.println(name+"进洞了！");
             try{
                 cave.wait();
             }
             catch(Exception e){}
                 System.out.println(name+"wait后代码");
         }
     }
 }

设置线程优先级

 class WaitDemo{
     public static void main(String[] args){
         Cave cave = new Cave();
         Car c1 = new Car("奔驰",cave);
         Car c2 = new Car("宝马",cave);
     
         //设置线程优先级
         Thread.currentThread().setPriority(Thread.MAX_PRIORITY);
         c1.setPriority(Thread.MIN_PRIORITY);
         c2.setPriority(Thread.NORM_PRIORITY);
         System.out.println("c1.priority:"+c1.getPriority());
         System.out.println("c2.priority:"+c2.getPriority());
         System.out.println("main.prio : " +Thread.currentThread().getPriority());
     
         c1.start();
         c2.start();

         try{
             Thread.sleep(5000);
             synchronized(cave){
                 cave.notifyAll();
             }
         }
         catch(Exception e){}
     }
 }

 class Cave{
 }
 
 class Car extends Thread{
     private String name;
     private Cave cave;
     public Car(String name, Cave cave){
         this.name = name;
         this.cave = cave;
     }
     
     public void run(){
         synchronized(cave){
             System.out.println(name+"进洞了！");
             try{
                 cave.wait();
             }
             catch(Exception e){}
             System.out.println(name+"wait后代码");
         }
     }
 }

作业讲解

一共100个馒头，40个工人，每个工人最多能吃3个馒头，使用多线程输出所有工人吃馒头的情况

 class ThreadDemo{
     public static void main(String[] args){
         Basket basket = new Basket();
         Worker w[] = new Worker[40];
         for(int i=0;i<40;i++){
             w[i] = new Worker("worker-"+i,basket);
         }
         for(int i=0;i<40;i++){
             w[i].start();
         }
     }
 }

 //放馒头的篮子
 class Basket{
     private int No = 100;

     //取馒头
     public int getNo(){
         if(No<=0){
             return -1;
         }
         else{
             return No--;
         }
     }
 }

 //工人线程类
 class Worker extends Thread{
     private static Basket basket;
     private String name;
     private int sumNo=0;//总共吃的馒头数

     public Worker(String name,Basket basket){
         this.basket = basket;
         this.name = name;
     }

     public void run(){
         while(true){
             synchronized(basket){
                 if(sumNo>=3){
                     return;
                 }
                 int no = basket.getNo();
                 if(no==-1){
                     return;
                 }
                 else{
                     sumNo++;
                     System.out.println(name+"吃了第"+no+"个馒头，共吃了"+sumNo+"个馒头");
                 }    
             }
             Thread.yield();
         }    
     }
 }

5辆汽车过隧道，隧道一次只能通过一辆汽车。每辆汽车通过时间不固定，
机动车通过时间3秒，三轮车通过时间5秒，畜力车通过时间10秒，5辆车分别是2辆机动车，2辆畜力车，1辆三轮车，通过多线程模拟通过隧道的情况。提示：Car ThreeCar CowCar

 class ThreadDemo{
     public static void main(String[] args){
         Cave cave = new Cave();
         new Car(cave,"汽车1",3).start();
         new Car(cave,"汽车2",3).start();
         new ThreeCar(cave,"三轮车",5).start();
         new CowCar(cave,"畜力车1",10).start();
         new CowCar(cave,"畜力车2",10).start();
     }
 }

 //隧道，山洞
 class Cave{
 }

 //机动车线程类
 class Car extends Thread{
     private Cave cave;
     private int sec;
     private String name;

     public Car(Cave cave, String name, int sec){
         this.cave = cave;
         this.name = name;
         this.sec = sec;
     }

     public void run(){
         synchronized(cave){
             System.out.println(name+"进洞了！"+new java.util.Date());
             try{
                 Thread.sleep(sec*1000);
             }
             catch(Exception e){}
             System.out.println(name+"出洞了！"+new java.util.Date());
         }
     }
 }

 //三轮车线程类
 class ThreeCar extends Thread{
     private Cave cave;
     private int sec;
     private String name;

     public ThreeCar(Cave cave, String name, int sec){
         this.cave = cave;
         this.name = name;
         this.sec = sec;
     }
     public void run(){
         synchronized(cave){
             System.out.println(name+"进洞了！"+new java.util.Date());
             try{
                 Thread.sleep(sec*1000);
             }
             catch(Exception e){}
             System.out.println(name+"出洞了！"+new java.util.Date());
         }
     }    
 }

 //畜力车线程类
 class CowCar extends Thread{
     private Cave cave;
     private int sec;
     private String name;

     public CowCar(Cave cave, String name, int sec){
         this.cave = cave;
         this.name = name;
         this.sec = sec;
     }    

     public void run(){
         synchronized(cave){
             System.out.println(name+"进洞了！"+new java.util.Date());
             try{
                 Thread.sleep(sec*1000);
             }
             catch(Exception e){}
             System.out.println(name+"出洞了！"+new java.util.Date());
         }
     }
 }

用多线程模拟蜜蜂和熊的关系
蜜蜂是生产者，熊是消费者，蜜蜂生产蜂蜜是累加的过程，熊吃蜂蜜是批量（满20吃掉）的过程，生产者和消费者之间使用通知方式告知对方，注意不能出现死锁现象。
100只蜜蜂，每次生产的蜂蜜是1
熊吃蜂蜜是20（批量的情况）

 class ThreadDemo{
     public static void main(String[] args){
         Pot pot = new Pot();
         for(int i=1;i<=100;i++){
             new Bee("蜜蜂-"+i,pot).start();
         }
         new Bear("熊大",pot).start();
         new Bear("熊二",pot).start();
     }
 }
 //蜜罐
 class Pot{
     private int MAX = 20;//最大值
     private int count;//当前量

     //添加蜂蜜，+1
     public synchronized int add(){
         while(count >= MAX){//若是if则下次进入线程，就不再去判断，存在问题
             try{
                 this.notifyAll();
                 this.wait();
             }
             catch(Exception e){
                 e.printStackTrace();
             }
         }
         return ++count;
     }

     //移除蜂蜜，-MAX
     public synchronized void remove(){
         while(count< MAX ){
             try{
                 this.wait();
             }
             catch(Exception e){
                 e.printStackTrace();
             }
         }
         count=0;
         this.notifyAll();
     }
 }
 //蜜蜂，生产者线程类
 class Bee extends Thread{
     private Pot pot;
     private String name;
     public Bee(String name, Pot pot){
         this.name = name;
         this.pot = pot;
     }
     public void run(){
         while(true){
             int n = pot.add();
             System.out.println(name+"生产了:"+n);
         }
     }
 }
 //熊，消费者线程类
 class Bear extends Thread{
     private Pot pot;
     private String name;
     public Bear(String name, Pot pot){
         this.name = name;
         this.pot = pot;
     }
     public void run(){
         while(true){
             pot.remove();
             System.out.println(name+"吃掉了蜂蜜:20!");
         }
     }
 }

创建线程的方式

继承Thread类

实现Runnable接口{public void run();}

 class Man extends Person implements Runnable{
     public void run(){
     ...
     }
 }

 new Car().start();
 new Thread(new Man()).start();

java.lang.Runnable

接口
public void run();
供现有类实现线程功能
使用Runnable对象创建线程
静态同步方式是使用class作为锁

非静态同步方式是使用当前对象作为锁

 new Thread(Runnable r).start();
 class Car implements Runnable{
 ...
 //静态同步方法
 static synchronized void xxx(){

 }
 }
 new Thread(Runnable r).start()

IDE

集成开发环境， integrate development environment
eclipse 快捷键：

alt + / //代码辅助
alt + 上箭头 //向上移动一行
alt + 下箭头 //向上移动一行
alt + shift + 上箭头 //向上复制一行
alt + shift + 下箭头 //向下复制一行
ctrl + D //删除一行
ctrl + shift + / //多行注释

String

常量

 String str = "xxx";
 str = "ddd";
 for(i<10000){
   name = name + "" + i;
 }//堆溢出
 byte b = (int)1234;
 //int a = (int)"123";
 //String name = (String)123;
 String name = 123 + "";

 Object o = new Dog();
 Dog d = (Dog)o;

创建String 的区别

 //一个对象
 String str1 = "abc";//在字符串池中开辟了空间
 //两个对象
 String str2 = new String("abc");//在堆区分配了内存空间

split(String s) // 按照指定的字符切割字符串，形成String数组
```
 "hello,,,world,".split(",");//最后的,不会生效
```
== //判断是否是同一对象。判断对象的内存地址
equals //是判断两个对象内容是否相同。
substring(int start) //取子串，包含start
substring(int start,int end) //取子串，前包后不包

重写subString(String src,int beginIndex,int length) //按索引及长度取子串，要有健壮性

 public static String subString(String src, int beginIndex, int length) throws Exception {
     if(src==null) {
         throw new Exception("源串为空");
     }
     if(!(beginIndex>=0 && beginIndex<src.length())) {
         throw new Exception("起始索引无效");
     }
     if(!(length>0 && (beginIndex+length)<=src.length())) {
         throw new Exception("长度无效");
     }
     return src.substring(beginIndex,beginIndex+length);
 }

包装类

byte Byte
short Short
int Integer
long Long
float Float
double Double
char Character
boolean Boolean

自动装箱：Integer i = 12; // Integer i = new Integer(12);
自动拆箱：Integer i =12; i++

包装类与基本数据类型区别

包装类是对象，默认值是null;
数字型基本数据类型默认是0；
基本数据类型可以直接参与运算；

编码初始

电报，电脑的传输，存储都是01010101

0000110 晚
1010100 上
0010100 喝
0010111 点
0000001 儿

000010 1010100 0010100 0010111 0000001

最早的'密码本'

ascii
7位二进制，涵盖了英文字母大小写，特殊字符，数字。
01000001 A
01000010 B
01000011 C
ascii，一个字节最多8位，只能表示256种可能，太少
存储单位换算
1bit 8bit = 1byte
1byte 1024byte = 1KB
1KB 1024kb = 1MB
1MB 1024MB = 1GB
1GB 1024GB = 1TB
万国码 unicode
- 起初：
  1个字节可以表示所有的英文，特殊字符，数字等等
  2个字节，16位表示一个中文，不够，unicode一个中文用4个字节，32位
  你 00000000 00000000 00000000 00001000
- Unicode 升级 utf-8 utf-16 utf-32
  utf-8 一个字符最少用8位去表示:
  1). 英文用8位一个字节
  2). 欧洲文字用16位去表示两个字节
  3). 中文用24位去表示三个字节
  utf-16 一个字符最少用16位去表示

gbk
中国人自己发明的，一个中文用两个字节，16位表示。

 String str = "a中b国c";
 byte[] bytes = str.getBytes("iso8859-1");
 System.out.println(bytes.length); //5, 欧洲码，没有中文字典
 System.out.println(new String(bytes,"iso8859-1")); //a?b?c
 
 bytes = str.getBytes("gbk");
 System.out.println(bytes.length); //7，一个字节表示英文字母，两个字节表示一个中文
 System.out.println(new String(bytes,"gbk")); //a中b国c
 
 bytes = str.getBytes("utf-8");
 System.out.println(bytes.length);//9， 英文一个字节，中文三个字节
 System.out.println(new String(bytes,"utf-8"));

 bytes = str.getBytes("unicode");// -2 -1 0 97 78 45 0 98 86 -3 0 99
 System.out.println(bytes.length);//12，中文四个字节，英文一个字节？为何是12？
 System.out.println(new String(bytes,"unicode"));
 
 String str2 = "a";
 byte[] bytes2 = str2.getBytes("unicode");//-2 -1 0 97

 String str3 = "中";
 byte[] bytes3= str3.getBytes("unicode");//-2 -1 78 45
 
 String str4 = "b";
 byte[] bytes4 = str4.getBytes("unicode");//-2 -1 0 98
  
 String str5 = "国";
 byte[] bytes5 = str5.getBytes("unicode");//-2 -1 86 -3
 
 String str6 = "c";
 byte[] bytes6 = str6.getBytes("unicode");//-2 -1 0 99

作业

substring(String str, int beginIndex, int length);
返回一定长度的子串
找到自己名字对应的Unicode码

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原文地址：https://www.cnblogs.com/SweetZxl/p/10079467.html