1、概念理解：

2、同步的解決方案：

1).基於代碼

synchronized 關鍵字

　修飾普通方法：作用於當前實例加鎖，進入同步代碼前要獲得當前實例的鎖。

　修飾靜態方法：作用於當前類對象加鎖，進入同步代碼前要獲得當前類對象的鎖。

修飾代碼塊：指定加鎖對象，對給定對象加鎖，進入同步代碼塊前要獲得給定對象的鎖。

code1

package com.thread;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

/**
 * 同步方法
 * @author Administrator
 *
 
 
*/
public class SynchronizedMethod implements Runnable{

    //靜態共享變量 i
    static int i = 0;
    
    /**
     * 自增
     */
    public synchronized void increase(){
        i++;
    }
    
    @Override
    public void run() {
        for (int j = 0; j < 100; j++) {
            increase();
        }
    }
    
    
 
public static void main(String[] args) throws InterruptedException {
        SynchronizedMethod instance = new SynchronizedMethod();
        ExecutorService executorService = Executors.newFixedThreadPool(2);
        for (int i = 0; i < 3; i++) {
            //同一實例，線程共享靜態變量i
//            executorService.execute(instance);
            
 
//不同實例，線程單獨享有變量i，達不到同步目的
            executorService.execute(new SynchronizedMethod());
            /**
             * 由於線程執行時間過短，在不同實例下，可能會得到類似於同步的結果。
             */
            Thread.sleep(100);
        }
        
        executorService.shutdown();
        
        System.out.println(i);  //300
        
    }
}

code2

package com.thread;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

/**
 * 同步代碼塊
 * @author Administrator
 *
 */
public class SynchronizedCodeBlock implements Runnable{

    //靜態共享變量 i
    static int i = 0;
    
    @Override
    public void run() {
        //同步進來的對象
        synchronized(this){  //SynchronizedCodeBlock.class
            for (int j = 0; j < 100; j++) {
                i++;
            }
        }
    }
    
    public static void main(String[] args) throws InterruptedException {
        SynchronizedCodeBlock instance = new SynchronizedCodeBlock();
        ExecutorService executorService = Executors.newFixedThreadPool(2);
        for (int i = 0; i < 3; i++) {
//            executorService.execute(instance);
            executorService.execute(new SynchronizedCodeBlock());
            Thread.sleep(10);
        }
        
        executorService.shutdown();
        
        System.out.println(i);  //300
        
    }
}

參考博客：

https://blog.csdn.net/javazejian/article/details/72828483

2).基於數據庫

Java高並發之同步異步