编写一个Java程序，实现以下功能

设计一个复数类，要求:
(1)在复数内部用双精度浮点数定义其实部和虚部;
(2)实现3个构造函数:无参(实部，虚部均为0)、1 个参数(参数赋值给实部，虚部为0)、2个参数(参数分别给实部虚部赋值);
(3)编写获取和修改复数的实部和虚部的成员方法;
(4)编写实现复数减法、乘法运算的成员方法;
(5)设计主方法，验证各成员方法的正确性;

ok，写好了：

public class Demo {
    public static void main(String[] args) {
        Complex complex1 = new Complex(20, 21);
        Complex complex2 = new Complex(19, 99);

        System.out.println("复数1为：" + complex1);
        System.out.println("复数2为：" + complex2);
        System.out.println("复数相减为：" + complex1.subtraction(complex2).toString());
        System.out.println("复数相乘为：" + complex1.multiplication(complex2).toString());
    }
}

/**
 * 复数类
 */
class Complex {
    private double real, imaginary;

    public Complex() {
        this(0, 0);
    }

    public Complex(double real) {
        this(real, 0);
    }

    public Complex(double real, double imaginary) {
        this.real = real;
        this.imaginary = imaginary;
    }

    public double getReal() {
        return real;
    }

    public void setReal(double real) {
        this.real = real;
    }

    public double getImaginary() {
        return imaginary;
    }

    public void setImaginary(double imaginary) {
        this.imaginary = imaginary;
    }

    /**
     * 复数的减法
     *
     * @param complex 减数
     * @return 相减以后的复数对象
     */
    public Complex subtraction(Complex complex) {
        return new Complex(this.getReal() - complex.getReal(), this.getImaginary() - complex.getImaginary());
    }

    /**
     * 复数的乘法
     *
     * @param complex 乘数
     * @return 相乘以后的复数对象 计算方法：(a+bi)(c+di)=(ac-bd)+(bc+ad)i。
     */
    public Complex multiplication(Complex complex) {
        double a = this.getReal(), b = this.getImaginary(), c = complex.getReal(), d = complex.getImaginary();
        return new Complex(a * c - b * d, b * c + a * d);
    }

    @Override
    public String toString() {
        return real + "+" + imaginary + "i";
    }
}