static关键词详解

static关键词详解

package com.oop.demo07;

//static
public class Student {
    private static int age;//静态变量
    private double score;//非静态变量

    public void run(){
        //go();
    }

    public static void go(){

    }

    public static void main(String[] args) {
        Student s1 = new Student();
        System.out.println(s1.age);
        System.out.println(s1.score);
        System.out.println(Student.age);
        //System.out.println(Student.score); //score 是非静态的，无法用类名直接调用

        new Student().run();
        go();
        Student.go();
    }
}

//----------------------------------------------------------------
package com.oop.demo07;
public class Person {

    //2.第二执行；可以用作赋初始值
    {
        System.out.println("匿名代码块");   //代码块 （匿名代码块）
    }
    //1.第一执行;且执行一次
    static {
        System.out.println("静态代码块"); //静态代码块
    }
    //3.第三执行
    public Person() {
        System.out.println("构造方法");
    }

    public static void main(String[] args) {
        Person person1 = new Person();
        System.out.println("============================");
        Person person2 = new Person();
    }
}

//--------------------------------------------------------------
package com.oop.demo07;
//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);
    }
}