对`static`关键字的理解

想请教一下爱学习的好朋友们：上面两行被static 关键字修饰的该怎么理解？

public class StaticDemo {
    static int x = 100;

    static {
        x = 48;
    }

    public StaticDemo() {
        x = 88;
    }

    public static void main(String[] args) {
        System.out.println("x=" + x);//48
    }
}