java - 这是初始化变量的正确方法吗

Question

在使用之前将 newWeight 设置为 0.0(在 switch block 之前)是一种不好的做法吗？如果我只是声明它，我会在编译器中收到一个错误，指出变量 newWeight 可能尚未初始化。

import java.util.*;

public class SpaceBoxing {
    public static void main(String[] args){
        Scanner s = new Scanner(System.in);
        System.out.print("Please enter your current weight ");
        float weight = s.nextFloat();

        System.out.println("I have information on the following planets");
        System.out.println("1. Venus  2. Mars   3. Jupiter");
        System.out.println("4. Saturn 5. Uranus 6. Neptune");
        System.out.println(" ");
        System.out.println("Which planet are you visiting");

        int planet = s.nextInt();
        double newWeight = 0.0;

        switch(planet){
            case 1:
                newWeight = weight*0.78;
                break;
            case 2:
                newWeight = weight*0.39;
                break;
            case 3:
                newWeight = weight*2.56;
                break;
            case 4:
                newWeight = weight*1.17;
                break;
            case 5:
                newWeight = weight*1.05;
                break;
            case 6:
                newWeight = weight*1.23;
                break;
        }
        System.out.println("Your weight would be " + newWeight + " pounds on that planet");
    }
}

Answer 1

您不需要在切换之前实例化它，但您应该在 switch 中包含一个 default 情况，在其中分配一个值或抛出一个 异常。如果前面的情况未涵盖提供的参数，则将执行默认情况。

int planet = s.nextInt();
double newWeight;

switch(planet){
    case 1:
        newWeight = weight*0.78;
        break;
    case 2:
        newWeight = weight*0.39;
        break;
    case 3:
        newWeight = weight*2.56;
        break;
    case 4:
        newWeight = weight*1.17;
        break;
    case 5:
        newWeight = weight*1.05;
        break;
    case 6:
        newWeight = weight*1.23;
        break;
    default:
        newWeight = 0.0;
        // or
        throw new IllegalArgumentException();
}