1. 什么实枚举？
在数学和计算机科学理论中，一个集的枚举是列出某些有穷序列集的所有成员的程序，或者是一种特定类型对象的计数。这两种类型经常（但不总是）重叠。是一个被命名的整型常数的集合，枚举在日常生活中很常见，例如表示星期的SUNDAY、MONDAY、TUESDAY、WEDNESDAY、THURSDAY、FRIDAY、SATURDAY就是一个枚举。
2. Java枚举内幕
通过下面Car.java文件及Car.class文件，大概就明白枚举是啥玩意了
Car.java
package com.github.whvixd.demo.enumDemo;
/**
* Created by wangzhx on 2018/6/28.
*/
public enum Car {
LAMBORGHINI,KOENIGSEGG
}
com.github.whvixd.Car.class;
$ javap Car.class
Compiled from "Car.java"
public final class Car extends java.lang.Enum<Car> {
public static final Car LAMBORGHINI;
public static final Car KOENIGSEGG;
public static Car[] values();
public static Car valueOf(java.lang.String);
static {};
}
为什么Enum中定义元素都是大写->这是规范！
枚举元素的修饰符:public static final，如下
package com.github.whvixd;
import com.github.whvixd.demo.enumDemo.Car;
import org.junit.Test;
import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
/**
* Created by wangzhx on 2018/6/28.
*/
public class TestEnum {
@Test
public void test() {
Class kClazz = Car.KOENIGSEGG.getClass();
Field[] fields = kClazz.getFields();
//遍历Car类的元素
for (Field field : fields) {
//判断元素的修饰符
if (Modifier.isPublic(field.getModifiers()) &&
Modifier.isStatic(field.getModifiers()) &&
Modifier.isFinal(field.getModifiers())) {
System.out.println(field.getName() + "元素的修饰符为 public static final");
}
}
}
}
/*
LAMBORGHINI元素的修饰符为 public static final
KOENIGSEGG元素的修饰符为 public static final
*/
知道枚举为什么是单例了吧
3. Java枚举的用法
1. 我们可以利用枚举写出优雅的代码
package com.github.whvixd.demo.enumDemo;
import lombok.Getter;
import lombok.Setter;
/**
* Created by wangzhx on 2018/6/28.
*/
public enum Car {
LAMBORGHINI("兰博基尼", 3E8), KOENIGSEGG("科尼赛克", 1E9);
@Setter
@Getter
private String carBrand;
@Setter
@Getter
private double price;
Car(String carBrand, double price) {
this.carBrand = carBrand;
this.price = price;
}
}
上面的代码与下面代码类似
package com.github.whvixd.demo.enumDemo;
import lombok.Getter;
import lombok.Setter;
/**
* Created by wangzhx on 2018/6/28.
*/
public class Car{
public static final Car LAMBORGHINI = new ICar("兰博基尼",3E8);
public static final Car KOENIGSEGG = new ICar("科尼赛克",1E9);
@Setter
@Getter
private String carBrand;
@Setter
@Getter
private double price;
Car(String carBrand, double price) {
this.carBrand = carBrand;
this.price = price;
}
}
2. 利用枚举写一个工厂模式
package com.github.whvixd.demo.enumDemo;
import lombok.Getter;
import lombok.Setter;
/**
* Created by wangzhx on 2018/6/28.
*/
public interface Factory {
enum Car{
LAMBORGHINI("兰博基尼", 3E8), KOENIGSEGG("科尼赛克", 1E9);
@Setter
@Getter
private String carBrand;
@Setter
@Getter
private double price;
Car(String carBrand, double price) {
this.carBrand = carBrand;
this.price = price;
}
}
interface ICar{
String printCarName(Car car);
}
//实现ICar接口
enum ICarImpl implements ICar{
LAMBORGHINI{
@Override
public String printCarName(Car car) {
//根据入参不同去写对应的逻辑
if("兰博基尼".equals(car.getCarBrand())){
return "兰博基尼";
}
return "";
}
},KOENIGSEGG {
@Override
public String printCarName(Car car) {
//根据入参不同去写对应的逻辑
if(1E9 == car.getPrice()){
return car.getCarBrand()+"价格："+car.getPrice();
}
return null;
}
}
}
}
测试
package com.github.whvixd;
import com.github.whvixd.demo.enumDemo.Car;
import com.github.whvixd.demo.enumDemo.Factory;
import org.junit.Assert;
import org.junit.Test;
/**
* Created by wangzhx on 2018/6/28.
*/
public class TestEnum {
@Test
public void testFactory() {
//创建入参创建对应的实例
Factory.ICar iCar = Factory.ICarImpl.valueOf(Car.KOENIGSEGG.name());
//用KOENIGSEGG这个对象去调用printCarName方法
Assert.assertSame("科尼赛克价格：1E9",
iCar.printCatName(Factory.Car.KOENIGSEGG));
}
}
