java enum

一、参考

Java Enums

二、enum

2.1 定义

constants: unchangeable variables, like final variables

An enum is a special "class" that represents a group of constants

2.2 创建

To create an enum,

(1) use the enum keyword (instead of class or interface),

(2) separate the constants with a comma.

(3) Note that they should be in uppercase letters

2.3 获取

You can access enum constants with the dot syntax

Enum is short for "enumerations", which means "specifically listed".

2.4 使用场景

Enums are often used in switch statements to check for corresponding values

The enum type has a values() method, which returns an array of all enum constants.

This method is useful when you want to loop through the constants of an enum

Use enums when you have values that you know aren't going to change, like month days, days, colors, deck of cards, etc.

2.5 与 class 比较

Difference between Enums and Classes

(1) An enum can, just like a class, have attributes and methods.

(2) The only difference is that enum constants are public, static and final (unchangeable - cannot be overridden).

(3) An enum cannot be used to create objects, and it cannot extend other classes (but it can implement interfaces)

2.6 示例

package basic;

public class EnumLearn {

    enum Level {
        LOW, MEDIUM, HIGH,
    }

    public static void main(String[] args) {

        // (1) 简单print
        printLevel();
        // (2) loop
        loopLevel();
        // (3) switch
        switchLevel();

    }

    // (1) 简单print
    public static void printLevel() {
        Level myVar = Level.MEDIUM;
        System.out.println("myVar: " + myVar);
    }

    // (2) loop
    public static void loopLevel() {
        for (Level myVar : Level.values()) {
            System.out.println(myVar);
        }
    }

    // (3) switch
    public static void switchLevel() {
        Level myVar = Level.MEDIUM;

        switch (myVar) {

            case LOW:
                System.out.println("Low level");
                break;

            case MEDIUM:

                System.out.println("Medium level");
                break;

            case HIGH:
                System.out.println("High level");
                break;

        }
    }

}