static

package com.ren;

public class Student {
    private static int age;//静态的变量  多线程
    private double score;//非静态的变量

    public void run(){

    }

    public static void go(){

    }

    public static void main(String[] args) {
        Student s1 = new Student();
        s1.score = 100;
        s1.age = 18;
        Student.age = 19;
        System.out.println(s1.age);
        Student.go();
        s1.run();
        go();
    }
}

package com.ren;

public class Person {

    {
        //匿名代码块  用于赋初始值
        System.out.println("匿名代码块");
    }

    static {
        //静态代码块  永久只执行一次
        System.out.println("静态代码块");
    }
    public Person(){
        System.out.println("构造方法");
    }

    public static void main(String[] args) {
        new Person();
        new Person();
    }
}

package com.ren;

//静态导入包
import static java.lang.Math.random;
import static java.lang.Math.PI;

public class Test {
    public static void main(String[] args) {
        System.out.println(random());
        System.out.println(PI);
    }
}