案例

package test;
class Person {
    public static int total;//静态变量
    static {//静态代码块
        total = 100;
        System.out.println("in static block!");//(1)
    }
}
class Test {
    public static void main(String[] args) {
        System.out.println("total = " + Person.total); //100
        System.out.println("total = " + Person.total); //100
    }
}

package test;
public class Main {
    //主方法
    public static void main(String str[]) {
        Test a = new Test();//无参构造器
    }
}
class Sample {
    Sample(String s) {
        System.out.println(s);
    }
}
class Test {
    Sample sam1 = new Sample("sam1成员初始化");
    static Sample sam = new Sample("静态成员sam初始化 ");
    static {
        System.out.println("static块执行");
        if (sam == null) {
            System.out.println("sam is null");
        }
    }
    Test() {//构造器
        System.out.println("Test默认构造函数被调用");
    }
}