Java object-oriented (seven)

enumerate

The introduction of enumerated (enum simulation)

class Student {
    private int restDay;

    public int getRestDay() {
        return restDay;
    }

    public void setRestDay(int restDay) {
        this.restDay = restDay;
    }
}

public class Test {
    public static void main(String[] args) {
        Student stu = new Student();
        stu.setRestDay(1);
        int res = stu.getRestDay();
        if (res == 6 || res == 7) {
            System.out.println("放假");
        } else {
            System.out.println("上课");
        }
    }
}

The above code, there are some problems:

(1) data is insecure, input 8

stu.setRestDay(8);  // 输出：上课（没有星期八）

(2) business logic of the irrational: the first day of the week is not the same as foreign, China is the first day on Monday, the first day of a foreign Zhou.

After the improvements:

class WeekDay {
    public static final int MONDAY = 1;
    public static final int TUESDAY = 2;
    public static final int WEDNESDAY = 3;
    public static final int THURSDAY = 4;
    public static final int FRIDAY = 5;
    public static final int SATURDAY = 6;
    public static final int SUNDAY = 7;
}

class Student {
    private int restDay;

    public int getRestDay() {
        return restDay;
    }

    public void setRestDay(int restDay) {
        this.restDay = restDay;
    }
}

public class Test {
    public static void main(String[] args) {
        Student stu = new Student();
        stu.setRestDay(WeekDay.MONDAY);
        int res = stu.getRestDay();
        if (res == 6 || res == 7) {
            System.out.println("放假");
        } else {
            System.out.println("上课");
        }
    }
}

The improved code, there are problems:

(1) data is insecure, input 8

stu.setRestDay(8);  // 输出：上课（没有星期八）

Improved again:

class WeekDay {
    private WeekDay() {}
    public static final WeekDay MONDAY = new WeekDay();
    public static final WeekDay TUESDAY = new WeekDay();
    public static final WeekDay WEDNESDAY = new WeekDay();
    public static final WeekDay THURSDAY = new WeekDay();
    public static final WeekDay FRIDAY = new WeekDay();
    public static final WeekDay SATURDAY = new WeekDay();
    public static final WeekDay SUNDAY = new WeekDay();
}

class Student {
    private WeekDay restDay;

    public WeekDay getRestDay() {
        return restDay;
    }

    public void setRestDay(WeekDay restDay) {
        this.restDay = restDay;
    }
}

public class Test {
    public static void main(String[] args) {
        Student stu = new Student();
        stu.setRestDay(WeekDay.MONDAY);
        WeekDay res = stu.getRestDay();
        if (res == WeekDay.SATURDAY || res == WeekDay.SUNDAY) {
            System.out.println("放假");
        } else {
            System.out.println("上课");
        }
    }
}

The code above solves the problem, but the code does not look good, too redundant.

What is an enumeration

Enumeration: Indicates a fixed state of things.

For example: season (spring, summer, autumn, winter), day of week (Monday to Sunday), gender (male and female)

The definition of enumeration

format:

[修饰符] enum 枚举的名称  {
    常量1，常量2，常量3……
}

such as:

enum Sex {
    MAN, FEMALE
}

Enumeration of nature

java enum is a syntax sugar . Is a special class, a collection of objects is more constants.

When we define an enumeration, its essence is a class, a class that inherits Enum.

enum Sex {
    MAN, FEMALE
}

Decompile after:

final class Sex extends Enum
{

    public static final Sex MAN;
    public static final Sex FEMALE;
    private static final Sex ENUM$VALUES[];

    private Sex(String s, int i)
    {
        super(s, i);
    }

    public static Sex[] values()
    {
        Sex asex[];
        int i;
        Sex asex1[];
        System.arraycopy(asex = ENUM$VALUES, 0, asex1 = new Sex[i = asex.length], 0, i);
        return asex1;
    }

    public static Sex valueOf(String s)
    {
        return (Sex)Enum.valueOf(Test/Sex, s);
    }

    static 
    {
        MAN = new Sex("MAN", 0);
        FEMALE = new Sex("FEMALE", 1);
        ENUM$VALUES = (new Sex[] {
            MAN, FEMALE
        });
    }
}