Java学习笔记 static的使用方法

package cn.itcast.day09.demo01;

public class Student {
          
   
    private String name;
    private int age;
    static String room;
    private int id;
    private static int idCounter = 0; //学号计数器,每new一个新对象 count++
    public Student(){
          
   
        this.id = ++idCounter;
    }

    public Student(String name, int age) {
          
   
        this.name = name;
        this.age = age;
        this.id = ++idCounter;
    }

    public String getName() {
          
   
        return name;
    }

    public void setName(String name) {
          
   
        this.name = name;
    }

    public int getAge() {
          
   
        return age;
    }

    public void setAge(int age) {
          
   
        this.age = age;
    }

    public int getId() {
          
   
        return id;
    }

    public void setId(int id) {
          
   
        this.id = id;
    }
}

package cn.itcast.day09.demo01;
/*若成员变量使用static关键字，此时变量属于类*/
public class Demo01StaticField {
          
   
    public static void main(String[] args) {
          
   
        Student one = new Student("gj",20);
        one.room = "101";
        System.out.println("name:"+one.getName()+"   age:"+one.getAge()+"    room:"+one.room);
        System.out.println("id is:"+one.getId());
        Student two = new Student("hr",21);
        System.out.println("name:"+two.getName()+"   age:"+two.getAge()+"    room:"+one.room);//static修饰，所有类共享
        System.out.println("id is:"+two.getId());
    }



}

package cn.itcast.day09.demo01;
/*static修饰成员方法就成为了静态方法，不属于对象，属于类
* 没用static修饰必须先创建对象才能使用
* 静态不能访问非静态 ：在内存中，现有静态内容后有非静态内容
* 静态方法不能使用this*/
public class Demo02StaticMethod {
          
   
    public static void main(String[] args) {
          
   
        MyClass obj = new MyClass();
        obj.method();//创建对象后才能使用
        //静态方法可以用对象名调用，也可通过类名称直接调用
        obj.methodStatic();//不推荐,编译后会被javac翻译成类名称.静态方法名
        MyClass.methodStatic();
        myMethod();//直接调用
    }
    public static void myMethod(){
          
   
        System.out.println("自己的方法");   //在本类中的静态方法可以省略名称
    }
}

package cn.itcast.day09.demo01;

public class MyClass {
          
   
    public void method(){
          
   
        System.out.println("这是成员方法");
    }
    public static void methodStatic(){
          
   
        System.out.println("这是静态方法");
    }
}

package cn.itcast.day09.demo01;
/*静态代码块*/
public class Person {
          
   
    static {
          
   
        System.out.println("静态方法被调用");//第一次使用本类时，静态方法调用唯一一次
    }
    public Person(){
          
   
        System.out.println("构造方法执行");
    }
}

package cn.itcast.day09.demo01;
/*静态方法一次性对静态变量进行赋值*/
public class Demo03Static {
          
   
    public static void main(String[] args) {
          
   
        Person one = new Person();//静态内容优先
        Person twp = new Person();//静态方法不再执行
    }
}