昨日内容回顾
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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 -
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
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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 CowCarclass 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
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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
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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
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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
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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
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 00001000Unicode 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
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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