Switch statement in constructor

Question

I want to create a Potion class with different effects, and my initial approach was to use a switch statement in the constructor to determine the potion's properties. However, this doesn't work because the Potion class inherits from a parent class, Item, which requires values like name and description. Since I need to call super in the constructor to pass these values, I'm struggling to find a way to implement the effect logic properly.

package Items;

public class Potion extends Item {
    private int effect;
    private int amount;


    public Potion(int effect, int amount) {

        switch(effect) {
            case 0 -> super("Potion of regeneration", "", "Potion");
            case 1 -> super("Potion of attack power", "", "Potion");
        }

        this.effect = effect;
        this.amount = amount;
    }
}

In the constructor super isn't a top level statement which it has to be. Is there any way I can work around this?

Answer 1

In current JDK the call to super must be first line, so you can adjust with these approaches:

public Potion(int effect, int amount) {
    super(effect==0 ? "Potion of regeneration": "Potion of attack power", "", "Potion");
    this.effect = effect;
    this.amount = amount;
}

If your case might be extended, use a helper function:

private static String potion(int effect) {
    return switch(effect) {
        case 0 -> "Potion of regeneration";
        case 1 -> "Potion of attack power";
        // Other values here ...
        default -> throw new IllegalArgumentException("Unexpected value: "+effect);
    };
}
public Potion(int effect, int amount) {
    super(potion(effect), "", "Potion");

    this.effect = effect;
    this.amount = amount;
}

JDK25 should provide flexible constructor bodies as part of JEP-513 which allow inline prologue before super:

public Potion(int effect, int amount) {
    String pe = switch(effect) {
        case 0 -> "Potion of regeneration";
        case 1 -> "Potion of attack power";
        // Other values here ...
        default -> throw new IllegalArgumentException("Unexpected value: "+effect);
    };
    super(pe, "", "Potion");
}

... which is a bit tidier than simply inserting the switch where pe is.