Multithreading important points and examples

Multithreading

What is multi-threading:

Multi-tasking multiple paths simultaneously perform multiple sequential streams multithreaded

The advantages of multi-threading:

Improve efficiency, while performing

Multithreading disadvantages:

Complex

Multithreaded created:

Thread class inheritance, override run () method, a method defined in the thread body RUN multithreaded

	/**
 * 线程创建方式
 * @author zhuch
 *
 */
public class ThreadTest extends Thread{

	@Override
	public void run() {
		for (int i = 0; i < 5; i++) {
			System.out.println("犯困");
		}
		
	}
	
	
	
	
	public static void main(String[] args) throws InterruptedException {
		//创建
		ThreadTest t=new ThreadTest();
		//开启
		t.start();
		
		// TODO Auto-generated method stub
		for (int i = 0; i < 5; i++) {
			System.out.println("瞌睡");
			Thread.sleep(100);
		}
	}

}

Implement Runnable, override run () method

recommend:

Avoid the limitations of single inheritance
Resource sharing

/**
 * 线程创建方式2
 * @author zhuch
 *
 */
public class RunnableTest implements Runnable{

	

	@Override
	public void run() {
		// TODO Auto-generated method stub
		for (int i = 0; i < 5; i++) {
			System.out.println("梦想");
		}
	}
	
	
	
	public static void main(String[] args) throws InterruptedException {
		// TODO Auto-generated method stub
		Thread t=new Thread(new RunnableTest());
		
		t.start();
		
		
		for (int i = 0; i < 5; i++) {
			System.out.println("远方");
			Thread.sleep(10);
		}
	}

}

Callable interface to achieve, rewrite method call

advantage:
1. You can throw an exception
2. Receiving a return value
Disadvantages: trouble

Security Thread:

Simultaneous operation of multiple threads with a thread may occur only resource problem of insecurity, the need to control security

Genlock:

synchronized

Queuing thread to execute the code for the {}
Sync block synchronized (locked content) {} synchronization code range
Lock content: this class .class resources (member variables)
Class .class equivalent to all the contents of this class, the class locked, like all objects are locked
The current members of this call object methods, resources equivalent to all the objects are locked, you can only lock resources
Resources: member variables, data types must refer to objects if the custom
Lock range: {} -> range of the code

note:

The lock is too large, inefficient
Lock range is too small, not lock
Lock same content

/**
 * 多线程打印12A23B45C67D...直到字母打印完结束
 * @author zhuch
 *
 */

public class Test {
	
	public static void main(String[] args) {
		//创建对象
		PrintTest pr=new PrintTest();
		//开启线程
		new Thread(new Number(pr)).start();
		new Thread(new CharTest(pr)).start();
		
	}

}

//行为
class PrintTest{
	//成员变量
	boolean flag=false;
	int num=1;
	char num1='A';
	//打印数字（同步块）
	public synchronized void number() {
		if(flag==true) {
			try {
				this.wait();
			} catch (InterruptedException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}else {
			try {
				Thread.sleep(200);
			} catch (InterruptedException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
			
			for(int i=0;i<2;i++) {
				if(num==53) {
					return;
				}
				System.out.print(num++);
			}
			
			flag=true;
			this.notify();
		}
	}
	
	//打印字母（同步块）
	public synchronized void charTest() {
		if(flag==false) {
			try {
				this.wait();
			} catch (InterruptedException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}else {
			try {
				Thread.sleep(200);
			} catch (InterruptedException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
			System.out.print((char)(num1++));
			flag=false;
			this.notify();
		}
	}
	
}
//数字类实现Runnable接口重写run方法
class Number implements Runnable{
	PrintTest pr=null;
	
	
	
	public Number(PrintTest pr) {
		super();
		this.pr = pr;
	}



	@Override
	public void run() {
		// TODO Auto-generated method stub
		while(true) {
			pr.number();
		}
	}
	
}
//字母类实现Runnable接口重写run方法
class CharTest implements Runnable{
	PrintTest pr=null;
	
	
	
	public CharTest(PrintTest pr) {
		super();
		this.pr = pr;
	}



	@Override
	public void run() {
		// TODO Auto-generated method stub
		while(true) {
			pr.charTest();
		}
	}
	
}

public class SynchronizedTest implements Runnable{
	Ticket ticket=new Ticket();
	
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		SynchronizedTest syn=new SynchronizedTest();
		new Thread(syn,"A").start();
		new Thread(syn,"B").start();
		new Thread(syn,"C").start();
	}

	@Override
	public void run() {
		// TODO Auto-generated method stub
		while(true) {
			synchronized(this) {
				if(ticket.num<=0) {
					break;
				}
				try {
					Thread.sleep(2);
				} catch (InterruptedException e) {
					// TODO Auto-generated catch block
					e.printStackTrace();
				}
				System.out.println(Thread.currentThread().getName()+"正在购买第"+ticket.num-- +"张票");
			}
		}
	}

}
class Ticket{
	int num=100;
}

Thread Status:

Newborn state: new to create a thread when
Ready state: start (), thread into the ready queue, waiting for the cpu scheduling
Operating status: cpu time slice allocated to the calling thread, the thread will run
Blocking state: sleep () ...
End state: the end of the thread
As soon as a thread to a blocking state, after unblocking, will not be restored immediately to run, it will return to the ready state, waiting for the cpu scheduling again
Once in the state to terminate a thread, never recover
How a thread into the ready state:
- 1.start()
- 2. unblocking
- 3. Thread switching is switched thread will be ready to state
- 4.yield () comity thread
Blocking the way into the state:
- 1.sleep
- 2.wait
- 3.join
How to control a thread termination:
- 1.stop ... not recommended
- 2. Analyzing represents
- 3. Normal execution ends
sleep (): thread to sleep
- 1) simulate latency
- 2) the possibility Magnification
- Let the cpu resources, will not let a lock object (to ensure that resources go to bed), specify how many milliseconds rest

public class StateTest implements Runnable{

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		StateTest sta=new StateTest();
		new Thread(sta,"A").start();
		new Thread(sta,"B").start();
	}

	@Override
	public void run() {
		// TODO Auto-generated method stub
		Thread t=new Thread(()-> {
			for (int i = 0; i < 20; i++) {
				System.out.println("插队");
				try {
					Thread.sleep(5);
				} catch (InterruptedException e) {
					// TODO Auto-generated catch block
					e.printStackTrace();
				}
			}
		});
		
		
		t.start();
		try {
			t.join();//方法插队
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		
		System.out.println(Thread.currentThread().getName()+"开始执行");
		Thread.yield();//礼让线程
		System.out.println(Thread.currentThread().getName()+"结束执行");
		
	}
	

}

Thread in getState () to obtain the status of a thread

Thread priority:

```
 提高先执行的概率
```
getPriority () returns the priority of the thread
setPriority (int newPriority) change the priority of this thread
- 10 1 ~ 10 1 Min 5 default maximum

public class StateDemo02 {
	public static void main(String[] args) {
		Thread th=new Thread(()->{
			for(int i=0;i<=10;i++){
				if(i==5){
					try {
						Thread.sleep(5);
					} catch (Exception e) {
						e.printStackTrace();
					}
				}
			}
		});
		th.setPriority(10);
		System.out.println(th.getPriority());
		
		System.out.println("th线程状态"+th.getState());
		th.start();
		
		while(true){
			Thread.State state=th.getState();
			System.out.println(state);
			if(state ==Thread.State.TERMINATED){
				break;
			}
			try {
				Thread.sleep(2);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
	}
}

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