静态代码块

package demo02;

import java.util.ArrayList;

public class Demo02Static {
    public static int number;
    public static ArrayList<String> list;

    static {
        // 给类变量赋值
        number = 2;
        list = new ArrayList<String>();
        // 添加元素到集合中
        list.add("张三");
        list.add("李四");
    }
}

package demo02;

public class Test {
    public static void main(String[] args) {
        //输出静态成员变量的值
        System.out.println(Demo02Static.number);//2
        System.out.println(Demo02Static.list);//[张三, 李四]

    }
}