Detailed explanation of the usage of enum (enumeration) in java

Java Enum principle:

public enum Size{ SMALL, MEDIUM, LARGE, EXTRA_LARGE };

In fact, the type defined by this declaration is a class, which has exactly four instances. Here Try not to construct new objects.

Therefore, when comparing the values ​​of two enumeration types, you never need to call the equals method, but just use "==" directly. (The equals() method also uses == directly, both have the same effect)

Related video tutorial recommendations: java teaching video

Usage 1: Constants

Before JDK1.5, the constants we defined were: public static fianl..... Well, now with enumerations, related constants can be grouped into an enumeration type, and enumerations provide more methods than constants.

public enum Color {  
  RED, GREEN, BLANK, YELLOW  
}

Usage 2: switch

The switch statement before JDK1.6 only supports int, char, and enum types. Using enumerations can make our code readable. Stronger sex.

enum Signal {
        GREEN, YELLOW, RED
    }

    public class TrafficLight {
        Signal color = Signal.RED;

        public void change() {
            switch (color) {
            case RED:
                color = Signal.GREEN;
                break;
            case YELLOW:
                color = Signal.RED;
                break;
            case GREEN:
                color = Signal.YELLOW;
                break;
            }
        }
    }

Usage 3: Add new methods to the enumeration

If you plan to customize your own method, you must add a semicolon at the end of the enum instance sequence. And Java requires that the enum instance must be defined first.

public enum Color {
    RED("红色", 1), GREEN("绿色", 2), BLANK("白色", 3), YELLO("黄色", 4);
    // 成员变量
    private String name;
    private int index;

    // 构造方法
    private Color(String name, int index) {
        this.name = name;
        this.index = index;
    }

    // 普通方法
    public static String getName(int index) {
        for (Color c : Color.values()) {
        if (c.getIndex() == index) {
            return c.name;
        }
        }
        return null;
    }

    // get set 方法
    public String getName() {
        return name;
    }

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

    public int getIndex() {
        return index;
    }

    public void setIndex(int index) {
        this.index = index;
    }
    }

Usage 4: Overriding the enumeration method

The following is an example of overriding the toString() method.

public class Test {
    public enum Color {
        RED("红色", 1), GREEN("绿色", 2), BLANK("白色", 3), YELLO("黄色", 4);
        // 成员变量
        private String name;
        private int index;

        // 构造方法
        private Color(String name, int index) {
            this.name = name;
            this.index = index;
        }

        // 覆盖方法
        @Override
        public String toString() {
            return this.index + "_" + this.name;
        }
    }

    public static void main(String[] args) {
        System.out.println(Color.RED.toString());
    }
}

Usage 5: Implement the interface

All enumerations inherit from the java.lang.Enum class. Since Java does not support multiple inheritance, enumeration objects cannot inherit from other classes.

public interface Behaviour {
    void print();

    String getInfo();
    }

    public enum Color implements Behaviour {
    RED("红色", 1), GREEN("绿色", 2), BLANK("白色", 3), YELLO("黄色", 4);
    // 成员变量
    private String name;
    private int index;

    // 构造方法
    private Color(String name, int index) {
        this.name = name;
        this.index = index;
    }

    // 接口方法

    @Override
    public String getInfo() {
        return this.name;
    }

    // 接口方法
    @Override
    public void print() {
        System.out.println(this.index + ":" + this.name);
    }
    }

Usage 6: Use interfaces to organize enumerations

public interface Food {
        enum Coffee implements Food {
            BLACK_COFFEE, DECAF_COFFEE, LATTE, CAPPUCCINO
        }

        enum Dessert implements Food {
            FRUIT, CAKE, GELATO
        }
    }

For more related articles and tutorials, please visit: Getting Started with Java

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