Java 两种简单的方式实现多线程

对于一些应用比如Server，需要对并发做出响应，那么需要用到多线程

两种实现多线程的方法：

• 继承 Thread 类
• 实现 Runnable 接口

继承 Thread 类

继承Thread类 必须重写run方法 ，然后调用start方法，即可执行

实现一个打印数字的线程类

package concurrent;

class printNumThread extends Thread
{
	String thname;
	printNumThread(String threadName) {
		this.thname = threadName;
	}
	
	public void run() {
		for(int i=0; i<=26; i++) {
			System.out.printf("Thread name: %s , print num: %d\n", thname, i);
			try {
				Thread.sleep(50);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
	}
}

public class mutilThread {
	public static void main(String[] args) {
		
		printNumThread pt1 = new printNumThread("线程A");
		pt1.start();
		
		printNumThread pt2 = new printNumThread("线程B");
		pt2.start();
	}
}

实现 Runnable 接口

实现Runnable接口，可以重新run，也可以不写，但是值得注意的是直接调用Runnable的run，不会开启多线程，需要在Thread类的构造函数种传入我们实现的Runnable接口的对象，才能开启

错误示范：实现一个打印字母的类，可以看到输出仍然是串行的

package concurrent;

class printCharThread implements Runnable {
	String thname;
	printCharThread(String threadName) {
		this.thname = threadName;
	}
	
	public void run() {
		for(char i='a'; i<='z'; i++) {
			System.out.printf("Thread name: %s , print char: %c\n", thname, i);
			try {
				Thread.sleep(50);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
	}
}

public class mutilThread {
	public static void main(String[] args) {
		
		printCharThread pt3 = new printCharThread("线程C");
		pt3.run();
		
		printCharThread pt4 = new printCharThread("线程D");
		pt4.run();
	}
}

正确方法：
在Thread类构造函数传入实现的Runnable，调用Thread类start方法

package concurrent;

class printCharThread implements Runnable {
	String thname;
	printCharThread(String threadName) {
		this.thname = threadName;
	}
	
	public void run() {
		for(char i='a'; i<='z'; i++) {
			System.out.printf("Thread name: %s , print char: %c\n", thname, i);
			try {
				Thread.sleep(50);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
	}
}

public class mutilThread {
	public static void main(String[] args) {
	
		printCharThread run3 = new printCharThread("线程C");
		Thread pt3 = new Thread(run3);
		pt3.start();
		
		printCharThread run4 = new printCharThread("线程D");
		Thread pt4 = new Thread(run4);
		pt4.start();
	}
}

两种方法：并行

package concurrent;

class printNumThread extends Thread
{
	String thname;
	printNumThread(String threadName) {
		this.thname = threadName;
	}
	
	public void run() {
		for(int i=0; i<=26; i++) {
			System.out.printf("Thread name: %s , print num: %d\n", thname, i);
			try {
				Thread.sleep(50);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
	}
}

class printCharThread implements Runnable {
	String thname;
	printCharThread(String threadName) {
		this.thname = threadName;
	}
	
	public void run() {
		for(char i='a'; i<='z'; i++) {
			System.out.printf("Thread name: %s , print char: %c\n", thname, i);
			try {
				Thread.sleep(50);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
	}
}

public class mutilThread {
	public static void main(String[] args) {
		
		printNumThread pt1 = new printNumThread("线程A");
		pt1.start();
		
		printNumThread pt2 = new printNumThread("线程B");
		pt2.start();
		
		printCharThread run3 = new printCharThread("线程C");
		Thread pt3 = new Thread(run3);
		pt3.start();
		
		printCharThread run4 = new printCharThread("线程D");
		Thread pt4 = new Thread(run4);
		pt4.start();
	}
}