java基础 韩顺平老师的 枚举和注解 自己记的部分笔记
424,枚举类引出
package com.hspedu.enum_;
public class Enumeration {
public static void main(String[] args) {
//使用
Season spring = new Season("春天","温暖");
Season summer = new Season("夏天","炎热");
Season autumn = new Season("秋天","凉爽");
Season winter = new Season("冬天","寒冷");
//这样也不合适,要固定才行
winter.setName("xxx");
winter.setDesc("非常的热");
//因为对于季节而言,它的对象(具体值),是固定的四个,不会有更多
//按老师的这个设计类的思路,不能体现季节是固定的四个对象
//因此,这样设计不好---> 引出枚举类[枚:一个一个 举:例举,即把具体的对象一个一个例举出来的类]
Season other = new Season("红天","~~~"); //这个对象间接表示季节不是固定的四个
}
}
class Season{
private String name;
private String desc;
public Season(String name, String desc) {
this.name = name;
this.desc = desc; //描述
}
public String getDesc() {
return desc;
}
public void setDesc(String desc) {
this.desc = desc;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
425,自定义枚举类
package com.hspedu.enum_;
import java.sql.SQLOutput;
public class Enumeration {
public static void main(String[] args) {
System.out.println(Season.SPRING);
}
}
//演示自定义枚举实现
class Season{
private String name;
private String desc;
//定义了四个对象吗,固定
public final static Season SPRING = new Season("春天","温暖");
public final static Season SUMMER = new Season("夏天","炎热");
public final static Season AUTUMN = new Season("秋天","凉爽");
public final static Season WINTER = new Season("冬天","寒冷");
//1,将构造器私有化,目的防止 直接 new
//2,去掉setXxx方法,防止属性被修改
//3,在Season内部,直接创建固定的对象
//4,优化,可以在定义静态对象那里加入 final 修饰符
private Season(String name, String desc) {
this.name = name;
this.desc = desc; //描述
}
public String getDesc() {
return desc;
}
public String getName() {
return name;
}
@Override
public String toString() {
return "Season{" +
"name='" + name + '\'' +
", desc='" + desc + '\'' +
'}';
}
}
426,enum枚举类1
package com.hspedu.enum_;
import java.sql.SQLOutput;
public class Enumeration {
public static void main(String[] args) {
System.out.println(Season.SPRING);
}
}
//演示使用enum关键字来实现枚举类
enum Season{
// //定义了四个对象吗,固定
// public final static Season SPRING = new Season("春天","温暖");
// public final static Season SUMMER = new Season("夏天","炎热");
// public final static Season AUTUMN = new Season("秋天","凉爽");
// public final static Season WINTER = new Season("冬天","寒冷");
//如果使用了enum来实现枚举类
//1,使用关键字 enum 替代 class
//2,public final static Season SPRING = new Season("春天","温暖") 直接使用下面的代码
// SPRING("春天","温暖") 解读 常量名(实参列表)
//3,如果有多个常量(对象),使用 , 号间隔即可
//4,如果使用enum 来实现枚举,要求将定义常量对象,写在前面
SPRING("春天","温暖"),SUMMER("夏天","炎热"),AUTUMN("秋天","凉爽"),WINTER("冬天","寒冷");
private String name;
private String desc;
private Season(String name, String desc) {
this.name = name;
this.desc = desc; //描述
}
public String getDesc() {
return desc;
}
public String getName() {
return name;
}
@Override
public String toString() {
return "Season{" +
"name='" + name + '\'' +
", desc='" + desc + '\'' +
'}';
}
}
427,enum枚举类2
第1点:
第3点
package com.hspedu.enum_;
import java.sql.SQLOutput;
public class Enumeration {
public static void main(String[] args) {
System.out.println(Season.What);
}
}
//演示使用enum关键字来实现枚举类
enum Season{
// //定义了四个对象吗,固定
// public final static Season SPRING = new Season("春天","温暖");
// public final static Season SUMMER = new Season("夏天","炎热");
// public final static Season AUTUMN = new Season("秋天","凉爽");
// public final static Season WINTER = new Season("冬天","寒冷");
//如果使用了enum来实现枚举类
//1,使用关键字 enum 替代 class
//2,public final static Season SPRING = new Season("春天","温暖") 直接使用下面的代码
// SPRING("春天","温暖") 解读 常量名(实参列表)
//3,如果有多个常量(对象),使用 , 号间隔即可
//4,如果使用enum 来实现枚举,要求将定义常量对象,写在前面
//5,如果我们使用的是无参构造器,创建常量对象,则可以省略 (),例如 What 或 What()
SPRING("春天","温暖"),SUMMER("夏天","炎热"),
AUTUMN("秋天","凉爽"),WINTER("冬天","寒冷"),
What();
private String name;
private String desc;
private Season() {//无参构造器
}
private Season(String name, String desc) {
this.name = name;
this.desc = desc; //描述
}
public String getDesc() {
return desc;
}
public String getName() {
return name;
}
@Override
public String toString() {
return "Season{" +
"name='" + name + '\'' +
", desc='" + desc + '\'' +
'}';
}
}
428,enum枚举类3
package com.hspedu.enum_;
import java.sql.SQLOutput;
public class Enumeration {
public static void main(String[] args) {
Gender2 boy = Gender2.BOY; //ok
Gender2 boy2 = Gender2.BOY; //ok
System.out.println(boy); //输出BOY
//本质就是调用Gender2 的父类 Enum的 toSpring方法
// public String toString() {
// return name;
// }
System.out.println(boy2 == boy); //True,返回的是同一个对象名
}
}
enum Gender2{ //会调用父类 Enum 的 toString,返回枚举对象名
BOY,GIRL;
}
429,Enum成员方法
位置号也是编号
package com.hspedu.enum_;
import java.lang.invoke.VarHandle;
import java.sql.SQLOutput;
public class EnumMethod {
public static void main(String[] args) {
//使用Season 枚举类,来演示各种方法
Season autumn = Season.AUTUMN;
//输出枚举对象的名字
System.out.println(autumn.name());
//ordinal() 输出的是该枚举对象的次序/编号,从0开始编号
//AUTUMN 枚举对象是第三个,因此输出 2
System.out.println(autumn.ordinal());
//从反编译(javap)可以看出 values方法,返回 Season[]
//含有定义的所有枚举对象
Season[] values = Season.values();
System.out.println("====遍历取出枚举对象(增强for)====");
for(Season season:values){ //增强for循环
System.out.println(season);
}
//valueOf:将字符串转换成枚举对象,要求字符串必须为已有的常量名,否则报异常
//执行流程
//1,根据你输入的 "AUTUMN" 到 Season的枚举对象去查找
//2,如果找到了,就返回,如果没有找到,就报错
Season autumn1 = Season.valueOf("AUTUMN");
System.out.println("autumn1 = " + autumn1);
System.out.println(autumn == autumn1);
//compareTo:比较两个枚举常量,比较的就是编号
//老韩解读
//1,就是把 Season.AUTUMN 枚举对象的编号 和 Season.SUMMER枚举对象的编号比较
//2,看看结果
/*
public final int compareTo(E o) {
// 省略了一些代码,自己想看可以点进去看
return self.ordinal - other.ordinal;
}
Season.AUTUMN的编号 - Season.SUMMER的编号 = 2-1=1
*/
System.out.println(Season.AUTUMN.compareTo(Season.SUMMER));
// //补充了一个增强for循环
// int[] nums = {1,2,9};
// //普通的for循环
// System.out.println("=====普通的for=====");
// for(int i = 0; i < nums.length; i++)
// {
// System.out.println(nums[i]);
// }
// System.out.println("======增强的for======");
// //执行的流程是 依次从nums数组中取出数据,赋给i,如果取出完毕,则退出for
// for(int i : nums)
// {
// System.out.println("i = " + i);
// }
}
}
430,Enum课堂练习
package com.hspedu.enum_;
public class EnumExercise {
public static void main(String[] args) {
//获取到所有的枚举对象,即数组
Week[] weeks = Week.values();
//遍历,使用增强for循环
System.out.println("=====所有星期的信息如下=====");
for (Week week : weeks) {
System.out.println(week);
}
}
}
enum Week{
//定义Week的枚举对象
MONDAY("星期一"),TUESDAY("星期二"), WEDNESDAY("星期三"),
THURSDAY("星期四"),FRIDAY("星期五"),SATURDAY("星期六"),SUNDAY("星期日");
private String name;
private Week(String name) { //构造器
this.name = name;
}
@Override
public String toString() { //重写toSring()方法
return name;
}
}
431,Enum使用细节
package com.hspedu.enum_;
public class EnumDetail {
public static void main(String[] args) {
Music.CLASSICMUSIC.playing();
}
}
class A {
}
//1,使用enum关键字后,就不能再继承其他类了,因为enum会隐式继承Enum,而Java是单继承机制
//enum Season extend A {
//}
//2,enum实现的枚举类,仍然是一个类,所以还是可以实现接口的
interface IPlaying{
public void playing();
}
enum Music implements IPlaying{
CLASSICMUSIC;
@Override
public void playing() {
System.out.println("播放好听的音乐...");
}
}
注解可以看老韩的笔记。
441,家庭作业6
package com.hspedu.enum_;
public class Homework {
public static void main(String[] args) {
//演示一下枚举值的switch使用
Color green = Color.GREEN;
green.show();
//比较一下
//switch() 中,放入枚举对象
//在每个case后,直接写上在枚举类中,定义的枚举对象即可
switch (green) {
case YELLOW:
System.out.println("匹配到黄色");
case BLACK:
System.out.println("匹配到黑色");
break;
case GREEN:
System.out.println("匹配到绿色");
break;
default:
System.out.println("没有匹配到...");
}
}
}
interface IMyInterface {
public void show();
}
enum Color implements IMyInterface{
//定义枚举对象
RED(255,0,0),BLUE(0,0,255),
BLACK(0,0,0),YELLOW(255,255,0),
GREEN(0,255,0);
private int redValue;
private int greenValue;
private int blueValue;
Color(int redValue, int greenValue, int blueValue) {
this.redValue = redValue;
this.greenValue = greenValue;
this.blueValue = blueValue;
}
@Override
public void show() {
System.out.println("属性值为" + redValue + "," + greenValue + "," + blueValue);
}
}