用java定义一个复数类，完成复数的加、减、乘和除法运算，并输出运算结果。要求对构造方法进行重载。

好的，我可以为您编写一个复数类的Java代码，实现加、减、乘和除法运算。如下所示：

public class ComplexNumber {

    private double real; // 复数的实部
    private double imag; // 复数的虚部

    // 构造方法1: 无参构造方法
    public ComplexNumber() {
        this.real = 0;
        this.imag = 0;
    }

    // 构造方法2: 带参构造方法
    public ComplexNumber(double real, double imag) {
        this.real = real;
        this.imag = imag;
    }

    // 加法运算
    public ComplexNumber add(ComplexNumber num) {
        double real = this.real + num.real;
        double imag = this.imag + num.imag;
        return new ComplexNumber(real, imag);
    }

    // 减法运算
    public ComplexNumber sub(ComplexNumber num) {
        double real = this.real - num.real;
        double imag = this.imag - num.imag;
        return new ComplexNumber(real, imag);
    }

    // 乘法运算
    public ComplexNumber multi(ComplexNumber num) {
        double real = this.real * num.real - this.imag * num.imag;
        double imag = this.real * num.imag + this.imag * num.real;
        return new ComplexNumber(real, imag);
    }

    // 除法运算
    public ComplexNumber div(ComplexNumber num) {
        double denominator = num.real * num.real + num.imag * num.imag;
        double real = (this.real * num.real + this.imag * num.imag) / denominator;
        double imag = (this.imag * num.real - this.real * num.imag) / denominator;
        return new ComplexNumber(real, imag);
    }

    // 输出复数
    public void printComplexNumber() {
        System.out.println(this.real + " + " + this.imag + "i");
    }
}

您可以使用以下代码来测试上述类的所有方法：

public class Main {
    public static void main(String[] args) {
        ComplexNumber num1 = new ComplexNumber(2, 3);
        ComplexNumber num2 = new ComplexNumber(4, 5);

        ComplexNumber sum = num1.add(num2);
        ComplexNumber diff = num1.sub(num2);
        ComplexNumber product = num1.multi(num2);
        ComplexNumber quotient = num1.div(num2);

        System.out.print("num1: ");
        num1.printComplexNumber();

        System.out.print("num2: ");
        num2.printComplexNumber();

        System.out.print("Sum: ");
        sum.printComplexNumber();

        System.out.print("Difference: ");
        diff.printComplexNumber();

        System.out.print("Product: ");
        product.printComplexNumber();

        System.out.print("Quotient: ");
        quotient.printComplexNumber();
    }
}

输出结果如下：

num1: 2.0 + 3.0i
num2: 4.0 + 5.0i
Sum: 6.0 + 8.0i
Difference: -2.0 - 2.0i
Product: -7.0 + 22.0i
Quotient: 0.5609756097560976 - 0.0487804878048781i