声明复数类Complex，成员变量包括实部和虚部，类型均为double。要求该类具有 (1)实现多个构造方法（如无参构造方法、1个参数构造方法，2个参数构造方法，字符串参数的构造方法）。 (2)使用getter和setter完成属性的访问和修改 (3)成员方法包括实现复数加法add、减法minus、乘法multiply，计算模长length (4)重写equals()方法，只有当两个复数实部和虚部都相等时，才返回真 (5)重写toString()，输出复数信息 (6)在main方法中，使用实际数据测试成员方法

好的，这是一个关于复数类 Complex 的代码实现：

public class Complex {
    private double realPart;    // 实部
    private double imaginaryPart;    // 虚部

    // 无参构造方法
    public Complex() {
        this.realPart = 0.0;
        this.imaginaryPart = 0.0;
    }

    // 1个参数构造方法
    public Complex(double realPart) {
        this.realPart = realPart;
        this.imaginaryPart = 0.0;
    }

    // 2个参数构造方法
    public Complex(double realPart, double imaginaryPart) {
        this.realPart = realPart;
        this.imaginaryPart = imaginaryPart;
    }

    // 字符串参数的构造方法
    public Complex(String complexString) {
        String[] parts = complexString.split("\\+|i");
        this.realPart = Double.parseDouble(parts[0]);
        this.imaginaryPart = Double.parseDouble(parts[1]);
    }

    // getter和setter
    public double getRealPart() {
        return realPart;
    }

    public void setRealPart(double realPart) {
        this.realPart = realPart;
    }

    public double getImaginaryPart() {
        return imaginaryPart;
    }

    public void setImaginaryPart(double imaginaryPart) {
        this.imaginaryPart = imaginaryPart;
    }

    // 复数加法
    public Complex add(Complex other) {
        double realPart = this.realPart + other.realPart;
        double imaginaryPart = this.imaginaryPart + other.imaginaryPart;
        return new Complex(realPart, imaginaryPart);
    }

    // 复数减法
    public Complex minus(Complex other) {
        double realPart = this.realPart - other.realPart;
        double imaginaryPart = this.imaginaryPart - other.imaginaryPart;
        return new Complex(realPart, imaginaryPart);
    }

    // 复数乘法
    public Complex multiply(Complex other) {
        double realPart = this.realPart * other.realPart - this.imaginaryPart * other.imaginaryPart;
        double imaginaryPart = this.realPart * other.imaginaryPart + this.imaginaryPart * other.realPart;
        return new Complex(realPart, imaginaryPart);
    }

    // 计算模长
    public double length() {
        return Math.sqrt(realPart * realPart + imaginaryPart * imaginaryPart);
    }

    // 重写equals()方法
    @Override
    public boolean equals(Object obj) {
        if (obj instanceof Complex) {
            Complex other = (Complex) obj;
            return this.realPart == other.realPart && this.imaginaryPart == other.imaginaryPart;
        }
        return false;
    }

    // 重写toString()方法
    @Override
    public String toString() {
        if (imaginaryPart >= 0) {
            return realPart + "+" + imaginaryPart + "i";
        } else {
            return realPart + "" + imaginaryPart + "i";
        }
    }

    // 测试
    public static void main(String[] args) {
        Complex c1 = new Complex(1.0, 2.0);
        Complex c2 = new Complex(3.0, 4.0);
        Complex c3 = new Complex("5+6i");

        System.out.println("c1 = " + c1.toString());
        System.out.println("c2 = " + c2.toString());
        System.out.println("c3 = " + c3.toString());

        System.out.println("c1 + c2 = " + c1.add(c2).toString());
        System.out.println("c1 - c2 = " + c1.minus(c2).toString());
        System.out.println("c1 * c2 = " + c1.multiply(c2).toString());

        System.out.println("c1.equals(c2) = " + c1.equals(c2));
        System.out.println("c1.equals(new Complex(1.0, 2.0)) = " + c1.equals(new Complex(1.0, 2.0)));

        System.out.println("|c1| = " + c1.length());
        System.out.println("|c2| = " + c2.length());
        System.out.println("|c3| = " + c3.length());
    }
}

在 main 方法中，我们进行了一些测试，输出结果如下：

c1 = 1.0+2.0i
c2 = 3.0+4.0i
c3 = 5.0+6.0i
c1 + c2 = 4.0+6.0i
c1 - c2 = -2.0-2.0i
c1 * c2 = -5.0+10.0i
c1.equals(c2) = false
c1.equals(new Complex(1.0, 2.0)) = true
|c1| = 2.23606797749979
|c2| = 5.0
|c3| = 7.810249675906654