关于JAVA中的static方法、并发问题以及JAVA运行时内存模型

package com.pichen.java.static_;

public class StaticTest {

    private static int s = 0;
    public static int sum(int n){
        s = 0;
        for(int i = 0; i <= n; i++){
            s += i;
            
            try {
                Thread.sleep(1);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        return s;
    }
}

package com.pichen.java.static_;


public class Main {

    public static void main(String[] args) {

        ThreadCount t1 = new ThreadCount();
        new Thread(t1).start();
        
        ThreadCount t2 = new ThreadCount();
        new Thread(t2).start();
        
        ThreadCount t3 = new ThreadCount();
        new Thread(t3).start();
    }
}