Java中浮点数比较的陷阱：理解double类型的不精确性与正确比较方法

import static org.assertj.core.api.Assertions.assertThat; // 假设使用AssertJ进行测试断言

public class DoubleComparisonExample {

    /**
     * 比较两个double值是否在给定容差范围内相等。
     *
     * @param d1      第一个double值
     * @param d2      第二个double值
     * @param epsilon 容差值，一个极小的正数
     * @return 如果两数之差的绝对值小于或等于epsilon，则返回true；否则返回false。
     */
    public static boolean areDoublesApproximatelyEqual(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;

        // 定义一个合适的容差值
        // 这个值需要根据你的业务需求和数据精度来确定
        // 例如，如果你关心小数点后6位，epsilon可以是0.000001
        double epsilon = 0.0000001; // 1e-7

        System.out.println("--- 示例1 ---");
        System.out.println("Dev: " + devValue1 + ", Local: " + localValue1);
        System.out.println("直接比较: " + (devValue1 == localValue1));
        System.out.println("容差比较 (epsilon=" + epsilon + "): " + areDoublesApproximatelyEqual(devValue1, localValue1, epsilon));
        // 使用AssertJ断言（在测试框架中常用）
        // assertThat(areDoublesApproximatelyEqual(devValue1, localValue1, epsilon)).isTrue();

        System.out.println("\n--- 示例2 ---");
        System.out.println("Dev: " + devValue2 + ", Local: " + localValue2);
        System.out.println("直接比较: " + (devValue2 == localValue2));
        System.out.println("容差比较 (epsilon=" + epsilon + "): " + areDoublesApproximatelyEqual(devValue2, localValue2, epsilon));

        System.out.println("\n--- 示例3 ---");
        System.out.println("Dev: " + devValue3 + ", Local: " + localValue3);
        System.out.println("直接比较: " + (devValue3 == localValue3));
        // 对于示例3，如果epsilon太小，可能仍然不相等，因为差异相对较大
        // devValue3 - localValue3 = -0.0000000224
        // 如果epsilon=0.0000001，则 Math.abs(-0.0000000224) < 0.0000001 为 true
        System.out.println("容差比较 (epsilon=" + epsilon + "): " + areDoublesApproximatelyEqual(devValue3, localValue3, epsilon));

        // 如果差异较大，即使使用epsilon也可能不相等
        double largeDiffDev = 10.0;
        double largeDiffLocal = 10.0001;
        System.out.println("\n--- 示例4 (较大差异) ---");
        System.out.println("Dev: " + largeDiffDev + ", Local: " + largeDiffLocal);
        System.out.println("容差比较 (epsilon=" + epsilon + "): " + areDoublesApproximatelyEqual(largeDiffDev, largeDiffLocal, epsilon));
    }
}

import static org.assertj.core.api.Assertions.assertThat;

// ... 在测试方法中
double actual = 9.7787576643837;
double expected = 9.778757664383699;
double tolerance = 0.0000001; // 1e-7

assertThat(actual).isCloseTo(expected, Assertions.offset(tolerance));