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复数在数学、科学或者工程领域是很常用的，可以通过调用Apache Commons Math库来完成，也可以自己手撸。

一、使用Apache Commons Math库

这个库有多个版本，在写这篇文章时，它的最新版是2022年12月19日的4.0-beta1，构建坐标是org.apache.commons:commons-math4-core:4.0-beta1，考虑到程序稳定性，我们可以使用目前开发者用得最多的版本3.6.1（2016年3月17日发布），Maven依赖如下：

<!-- https://mvnrepository.com/artifact/org.apache.commons/commons-math3 -->
<dependency><groupId>org.apache.commons</groupId><artifactId>commons-math3</artifactId><version>3.6.1</version>
</dependency>

示例代码如下：

import org.apache.commons.math3.complex.Complex;
public class ACMComplexDemo {public static void main(String[] args) {Complex c = new Complex(3, 5);Complex d = new Complex(2, -2);System.out.println(c);System.out.println("c = " + c.getReal() + " + " + c.getImaginary() + "i");System.out.println(c + " * " + d + " = " + c.multiply(d));System.out.println(c + " / " + d + " = " + c.divide(d));}
}

二、自己开发一个复数类

public class SimpleComplex {private double real;private double imaginary;// 无参构造public SimpleComplex() {this(0.0, 0.0);}// 双参构造，用于表示虚数public SimpleComplex(double real, double imaginary) {this.real = real;this.imaginary = imaginary;}// 单参构造，适用于实数范围public SimpleComplex(double real) {this(real, 0.0);}// 加法public SimpleComplex add(SimpleComplex other) {double real = this.real + other.real;double imaginary = this.real + other.imaginary;return new SimpleComplex(real, imaginary);}// 减法public SimpleComplex sub(SimpleComplex other) {return this.add(opposite(other));}// 乘法public SimpleComplex mul(SimpleComplex other) {double real = this.real * other.real - this.imaginary * other.imaginary;double imaginary = this.real * other.imaginary + this.imaginary * other.real;return new SimpleComplex(real, imaginary);}// 除法public SimpleComplex div(SimpleComplex other) {double real = (this.real * other.real + this.imaginary * other.imaginary)/ (other.real * other.real + other.imaginary * other.imaginary);double imaginary = (this.imaginary * other.real - this.real * other.imaginary)/ (other.real * other.real + other.imaginary * other.imaginary);return new SimpleComplex(real, imaginary);}// 获取实部public double getReal() {return real;}// 获取虚部public double getImaginary() {return imaginary;}@Overridepublic String toString() {if (this.real == 0.0) {return this.imaginary + "i";} else if (this.imaginary == 0.0) {return this.real + "";} else if (this.imaginary < 0.0 && this.real != 0.0) {return this.real + "" + this.imaginary + "i";} else if (this.imaginary == 0.0 && this.real == 0.0) {return "0.0";}return this.real + "+" + this.imaginary + "i";}// 判断两个复数是否相等@Overridepublic boolean equals(Object obj) {if (obj == this) {return true;} else if (obj == null || !(obj instanceof SimpleComplex)) {return false;}SimpleComplex tmp = (SimpleComplex) obj;return Math.abs(this.real - tmp.real) < 1e-6&& Math.abs(this.imaginary - tmp.imaginary) < 1e-6;}// 返回相反数private static SimpleComplex opposite(SimpleComplex one) {return new SimpleComplex(-one.real, -one.imaginary);}public static void main(String[] args) {// 示例用法SimpleComplex c1 = new SimpleComplex(3, 5); // 3 + 5iSimpleComplex c2 = new SimpleComplex(2, -2); // 2 - 2iSystem.out.println("c1 + c2 = " + c1.add(c2));System.out.println("c1 - c2 = " + c1.sub(c2));System.out.println("c1 * c2 = " + c1.mul(c2));System.out.println("c1 / c2 = " + c1.div(c2));}
}

显然，自己开发一个并不如Apache Commons Math做得好了，毕竟Apache的库提供了大量的运算方法，且逻辑严谨，是应用开发的首选。但执行一些简单的运算，譬如复数除法，在一定量的基础上，简单实现有一点点的性能优势。