homework/PercentageDiscountStrategy.java

public class PercentageDiscountStrategy implements DiscountStrategy {
    private double discountPercentage; // 折扣百分比，例如0.1表示10%折扣
    
    /**
     * 构造百分比折扣策略
     * @param discountPercentage 折扣百分比（0-1之间的值）
     */
    public PercentageDiscountStrategy(double discountPercentage) {
        if (discountPercentage < 0 || discountPercentage > 1) {
            throw new IllegalArgumentException("折扣百分比必须在0到1之间");
        }
        this.discountPercentage = discountPercentage;
    }
    
    @Override
    public double calculateDiscount(Order order) {
        if (order == null) {
            return 0;
        }
        // 计算折扣金额：订单金额 * 折扣百分比
        return order.getAmount() * discountPercentage;
    }
    
    @Override
    public String getDescription() {
        // 将百分比转换为整数表示，例如0.1转换为10%
        return (int)(discountPercentage * 100) + "%折扣"; 
    }
}