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

下面是实现上述要求的复数类 Complex：

public class Complex {
    private double real;
    private double imaginary;
    
    public Complex() {
        this.real = 0.0;
        this.imaginary = 0.0;
    }
    
    public Complex(double real) {
        this.real = real;
        this.imaginary = 0.0;
    }
    
    public Complex(double real, double imaginary) {
        this.real = real;
        this.imaginary = imaginary;
    }
    
    public Complex(String complexString) {
        String[] parts = complexString.split("\\+|i");
        this.real = Double.parseDouble(parts[0]);
        this.imaginary = Double.parseDouble(parts[1]);
    }
    
    public double getReal() {
        return this.real;
    }
    
    public double getImaginary() {
        return this.imaginary;
    }
    
    public void setReal(double real) {
        this.real = real;
    }
    
    public void setImaginary(double imaginary) {
        this.imaginary = imaginary;
    }
    
    public Complex add(Complex other) {
        double real = this.real + other.real;
        double imaginary = this.imaginary + other.imaginary;
        return new Complex(real, imaginary);
    }
    
    public Complex minus(Complex other) {
        double real = this.real - other.real;
        double imaginary = this.imaginary - other.imaginary;
        return new Complex(real, imaginary);
    }
    
    public Complex multiply(Complex other) {
        double real = this.real * other.real - this.imaginary * other.imaginary;
        double imaginary = this.real * other.imaginary + this.imaginary * other.real;
        return new Complex(real, imaginary);
    }
    
    public double length() {
        return Math.sqrt(this.real * this.real + this.imaginary * this.imaginary);
    }
    
    @Override
    public boolean equals(Object other) {
        if (this == other) {
            return true;
        }
        if (!(other instanceof Complex)) {
            return false;
        }
        Complex otherComplex = (Complex) other;
        return this.real == otherComplex.real && this.imaginary == otherComplex.imaginary;
    }
    
    @Override
    public String toString() {
        if (this.imaginary >= 0) {
            return String.format("%.2f+%.2fi", this.real, this.imaginary);
        } else {
            return String.format("%.2f%.2fi", this.real, this.imaginary);
        }
    }
    
    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());
        
        Complex c4 = c1.add(c2);
        System.out.println("c1 + c2 = " + c4.toString());
        
        Complex c5 = c1.minus(c2);
        System.out.println("c1 - c2 = " + c5.toString());
        
        Complex c6 = c1.multiply(c2);
        System.out.println("c1 * c2 = " + c6.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，我们按照要求使用了实际数据来测试了成员方法。