Java中双精度浮点数比较的陷阱与解决方案

// 示例1
6764785.117418662  (开发环境)
6764785.11741866   (本地环境)

// 示例2
9.7787576643837    (开发环境)
9.778757664383699  (本地环境)

// 示例3
2.0465350497710526 (开发环境)
2.046535049771075  (本地环境)

import static org.assertj.core.api.Assertions.assertThat; // 假设使用AssertJ断言库

public class DoubleComparisonUtil {

    /**
     * 比较两个double值是否在给定的epsilon范围内相等。
     *
     * @param d1      第一个double值
     * @param d2      第二个double值
     * @param epsilon 允许的最大差值
     * @return 如果两个值在epsilon范围内相等，则返回true；否则返回false。
     */
    public static boolean areDoublesEqual(double d1, double d2, double epsilon) {
        return Math.abs(d1 - d2) < epsilon;
    }

    public static void main(String[] args) {
        double devValue1 = 6764785.117418662;
        double localValue1 = 6764785.11741866;

        double devValue2 = 9.7787576643837;
        double localValue2 = 9.778757664383699;

        double devValue3 = 2.0465350497710526;
        double localValue3 = 2.046535049771075;

        // 定义一个合适的epsilon值
        // 通常根据业务需求和期望的精度来选择，例如1e-6 (0.000001)
        double epsilon = 0.00000001; // 10^-8

        System.out.println("--- 示例1 ---");
        System.out.println("开发环境: " + devValue1);
        System.out.println("本地环境: " + localValue1);
        System.out.println("使用epsilon比较结果: " + areDoublesEqual(devValue1, localValue1, epsilon));
        // 使用AssertJ进行断言 (仅作演示)
        assertThat(areDoublesEqual(devValue1, localValue1, epsilon)).isTrue();


        System.out.println("\n--- 示例2 ---");
        System.out.println("开发环境: " + devValue2);
        System.out.println("本地环境: " + localValue2);
        System.out.println("使用epsilon比较结果: " + areDoublesEqual(devValue2, localValue2, epsilon));
        assertThat(areDoublesEqual(devValue2, localValue2, epsilon)).isTrue();


        System.out.println("\n--- 示例3 ---");
        System.out.println("开发环境: " + devValue3);
        System.out.println("本地环境: " + localValue3);
        System.out.println("使用epsilon比较结果: " + areDoublesEqual(devValue3, localValue3, epsilon));
        // 注意：对于示例3，差值较大，即使是1e-8的epsilon可能也不够，需要根据实际需求调整
        // |2.0465350497710526 - 2.046535049771075| = 0.0000000000000224
        // 这里的差值是 2.24 * 10^-14，小于 10^-8
        assertThat(areDoublesEqual(devValue3, localValue3, epsilon)).isTrue();


        // 演示不相等的情况
        double d1 = 10.000001;
        double d2 = 10.000003;
        double smallEpsilon = 0.000001; // 10^-6
        System.out.println("\n--- 演示不相等 ---");
        System.out.println("d1: " + d1 + ", d2: " + d2);
        System.out.println("epsilon: " + smallEpsilon);
        System.out.println("使用epsilon比较结果: " + areDoublesEqual(d1, d2, smallEpsilon));
        assertThat(areDoublesEqual(d1, d2, smallEpsilon)).isFalse();
    }
}