如何排查Java实例方法调用情况并修正FunPark类折扣计算逻辑错误

你的代码逻辑核心问题在于：你用已经打过折扣的totalPrice值来判断用户已选活动。一旦应用折扣后，totalPrice不再是原价的累加值，后续的条件判断自然会失效。

举个例子拆解你的调用流程：

1. 调用park.trampoline()：totalPrice被设为12（蹦床原价）
2. 调用park.climbWall()：此时totalPrice是12，符合第一个if条件（等于蹦床原价），先加攀岩的10元变成22，再打10折得到19.8，totalPrice现在是19.8
3. 调用park.waterSlide()：此时判断totalPrice是否等于攀岩+蹦床的原价总和22，但当前totalPrice是19.8，不匹配条件，所以走else分支直接把totalPrice设为水滑梯的15元——这就是你得到15.0的原因。

正确思路是单独记录用户已选活动的数量（或具体活动），不依赖折扣后的价格反推。这里提供两种简洁的修正方式：

方式1：用计数+原价累加（无重复选择限制） #

这种方式适合不考虑用户重复选择同一活动的场景，逻辑最简洁：

public class FunPark {
    private final int climbWallPrice = 10;
    private final int trampoliningPrice = 12;
    private final int waterSlidesPrice = 15;
    private int selectedActivityCount = 0;
    private float originalTotal = 0;

    public float getTotalPrice() {
        if (selectedActivityCount == 2) {
            return applyDiscountTo(originalTotal, 10);
        } else if (selectedActivityCount == 3) {
            return applyDiscountTo(originalTotal, 20);
        }
        return originalTotal;
    }

    private float applyDiscountTo(float applyTo, int discountInPercent) {
        return applyTo * (1 - (float) discountInPercent / 100);
    }

    public void climbWall() {
        originalTotal += climbWallPrice;
        selectedActivityCount++;
    }

    public void trampoline() {
        originalTotal += trampoliningPrice;
        selectedActivityCount++;
    }

    public void waterSlide() {
        originalTotal += waterSlidesPrice;
        selectedActivityCount++;
    }
}

方式2：支持防重复选择（更严谨） #

如果需要避免用户重复选择同一活动，可以用集合记录已选活动，再根据集合大小计算折扣：

import java.util.HashSet;
import java.util.Set;

public class FunPark {
    private final int climbWallPrice = 10;
    private final int trampoliningPrice = 12;
    private final int waterSlidesPrice = 15;
    private final Set<String> selectedActivities = new HashSet<>();

    public float getTotalPrice() {
        float originalTotal = calculateOriginalTotal();
        int count = selectedActivities.size();
        if (count == 2) {
            return applyDiscountTo(originalTotal, 10);
        } else if (count == 3) {
            return applyDiscountTo(originalTotal, 20);
        }
        return originalTotal;
    }

    private float calculateOriginalTotal() {
        float total = 0;
        if (selectedActivities.contains("climbWall")) total += climbWallPrice;
        if (selectedActivities.contains("trampoline")) total += trampoliningPrice;
        if (selectedActivities.contains("waterSlide")) total += waterSlidesPrice;
        return total;
    }

    private float applyDiscountTo(float applyTo, int discountInPercent) {
        return applyTo * (1 - (float) discountInPercent / 100);
    }

    public void climbWall() {
        selectedActivities.add("climbWall");
    }

    public void trampoline() {
        selectedActivities.add("trampoline");
    }

    public void waterSlide() {
        selectedActivities.add("waterSlide");
    }
}

用你的Main类调用修正后的代码：

public class Main {
    public static void main(String[] args) {
        FunPark park = new FunPark();
        park.trampoline();
        park.climbWall();
        park.waterSlide();
        System.out.println(park.getTotalPrice()); // 输出29.6，符合预期
    }
}

内容的提问来源于stack exchange，提问作者zeplika