執行緒的概念：

大白話的意思就是，執行緒存在於程序中，它主要是為了提程序中CPU（程序有記憶體，執行緒沒有）的利用率，即提高效率。

主執行緒：執行main方法的執行緒，是它產生其他執行緒，通常它是最後結束，因為它要執行關閉其他執行緒的工作，它不會直接關閉其他執行緒，而只是傳送指令過去。

java實現多執行緒的方式

1. 繼承Thread類
2. 實現Runnable介面
3. 實現Callable介面

java基礎學習時實現多執行緒的方式主要學習前面兩種，callable是後面產生的

下面通過一個案例來理解多執行緒：模擬燒水，洗茶杯與泡茶過程

Demo1:

package test;

import java.util.concurrent.CountDownLatch;

public class ThreadTest {

	private static boolean isok = false; 
	static final CountDownLatch countdown = new CountDownLatch(1);
	
	
	public static void main(String[] args) {
		
		final Object lock = new Object();
		
		Thread washThread = new Thread(new Runnable() {
			public void run() {
				for(int i=1;i<=5;i++) {
					
					System.out.println("washing："+i);
					try {
						Thread.sleep(1500);
					} catch (InterruptedException e) {
						e.printStackTrace();
					}
					if(i==3) {
						System.out.println("發出通知");
						countdown.countDown();
					}
				}
			}
			
		},"washthread");
		
		Thread boilThread = new Thread(new Runnable() {

			public void run() {
				
					try {
						countdown.await();
					} catch (InterruptedException e) {
						e.printStackTrace();
					}
					System.out.println("收到通知...make tea...");
			}
			
		},"boilthread");
		
		washThread.start();
		boilThread.start();
	}
}
 

Demo2:

package test;

import java.util.concurrent.CountDownLatch;

public class ThreadTest {

	private static boolean isok = false; 
	static final CountDownLatch countdown = new CountDownLatch(2);
	
	
	public static void main(String[] args) {
		
		final Object lock = new Object();
		
		Thread washThread = new Thread(new Runnable() {
			public void run() {
				for(int i=1;i<=5;i++) {
					
					System.out.println("washing："+i);
					try {
						Thread.sleep(1500);
					} catch (InterruptedException e) {
						e.printStackTrace();
					}
				}
				System.out.println("發出通知");
				countdown.countDown();
			}
			
		},"washthread");
		
		Thread boilThread = new Thread(new Runnable() {

			public void run() {
				
					try {
						Thread.sleep(5000);
					} catch (InterruptedException e) {
						e.printStackTrace();
					}
					System.out.println("收到通知...make tea...");
					countdown.countDown();
			}
			
		},"boilthread");
		Thread maketeaThread = new Thread(new Runnable() {

			public void run() {
				
					try {
						countdown.await();
					} catch (InterruptedException e) {
						e.printStackTrace();
					}
					System.out.println("收到通知... 喝茶...");
			}
			
		},"maketeathread");
		washThread.start();
		boilThread.start();
		maketeaThread.start();
	}
}