【Java】最近のSwitch文の書き方を試してみる

先日JavaをJava13へアップグレードしました。

私が仕事で使っていたJavaのバージョンは7でしたのでこの間に書き方にも様々な変更がありました。その中でも今回は今風のswitch文を紹介したいと思います。

書き方

switch文と言えば今までは以下のように書いていました。

public class Main {

    public static void main(String[] args) {

        int dayValue = 2;
        String week = "default";

        switch(dayValue){
            case 1:
                week = "Monday";
                break;
            case 2:
                week = "Tuesday";
                break;
            case 3:
                week = "Wednesday";
                break;
            case 4:
                week = "Thursday";
                break;
            case 5:
                week = "Friday";
                break;
            case 6:
                week = "Saturday";
                break;
            case 7:
                week = "Sunday";
                break;
            default:
        }
        System.out.println(week);
    }
}

public class Main {

public static void main(String[] args) {

int dayValue = 2;

String week = "default";

switch(dayValue){

case 1:

week = "Monday";

break;

case 2:

week = "Tuesday";

break;

case 3:

week = "Wednesday";

break;

case 4:

week = "Thursday";

break;

case 5:

week = "Friday";

break;

case 6:

week = "Saturday";

break;

case 7:

week = "Sunday";

break;

default:

}

System.out.println(week);

}

switch文は見た目にもわかりやすく、初心者にも使いやすい文だと思います。

しかしケースが増えると行数が増えて見づらくなったり、時にはbreakが抜けてしまってバグの原因になることもありました。これが最近のJava以下のように書くことが出来ます。

public class Main {

    public static void main(String[] args) {

        int dayValue = 2;
        String week = "default";
        switch(dayValue){
            case 1 -> week = "Monday";
            case 2 -> week = "Tuesday";
            case 3 -> week = "Wednesday";
            case 4 -> week = "Thursday";
            case 5 -> week = "Friday";
            case 6 -> week = "Saturday";
            case 7 -> week = "Sunday";
        };
        System.out.println(week);
    }
}

public class Main {

public static void main(String[] args) {

int dayValue = 2;

String week = "default";

switch(dayValue){

case 1 -> week = "Monday";

case 2 -> week = "Tuesday";

case 3 -> week = "Wednesday";

case 4 -> week = "Thursday";

case 5 -> week = "Friday";

case 6 -> week = "Saturday";

case 7 -> week = "Sunday";

};

System.out.println(week);

}

breakを書かなくてもcase内で止まるようになり、見た目にも簡潔になっています。

さらに以下のように条件をまとめて書くことも可能です。

public class Main {

    public static void main(String[] args) {

        int dayValue = 8;
        String week = "default";
        switch(dayValue){
            case 1 -> week = "Monday";
            case 2 -> week = "Tuesday";
            case 3 -> week = "Wednesday";
            case 4 -> week = "Thursday";
            case 5 -> week = "Friday";
            case 6 -> week = "Saturday";
            case 7,8,9 -> week = "Sunday";
        };
        System.out.println(week);
    }
}