. 创建一个复数类Complex，对复数进行数学运算

【问题描述】
创建一个复数类Complex，对复数进行数学运算，复数具有如下格式：realPart+imaginaryPart*i，其中，i为-1的平方根，具体要求如下：
（１）利用浮点变量表示此类的私有数据。提供两个构造方法，一个用于此类声明时对象的初始化；一个为带默认值得无参构造方法。
（２）提供两复数加、减、乘的运算方法。
（３）按格式(a,b)打印复数，其中a为实部，b为虚部。

import java.util.Scanner;

public class Test {
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		System.out.println("input c1:");
		double r1 = in.nextDouble();
		double ima1 = in.nextDouble();
		System.out.println("input c2:");
		double r2 = in.nextDouble();
		double ima2 = in.nextDouble();
		Complex c1 = new Complex(r1, ima1);
		Complex c2 = new Complex(r2, ima2);
		System.out.println("ComplexNumber a: "+c1);
		System.out.println("ComplexNumber b: "+c2);
		System.out.println("(a + b) = " + c1.add(c2));
		System.out.println("(a - b) = " + c1.sub(c2));
		System.out.println("(a * b) = " + c1.mul(c2));

	}
}

class Complex {
	private double real, imaginary;

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

	Complex() {

	}

	public Complex add(Complex other) {
		Complex t = new Complex(0, 0);
		t.real = this.real + other.real;
		t.imaginary = this.imaginary + other.imaginary;
		return t;
	}

	public Complex sub(Complex other) {
		Complex t = new Complex(0, 0);
		t.real = this.real - other.real;
		t.imaginary = this.imaginary - other.imaginary;
		return t;
	}

	public Complex mul(Complex other) {
		Complex t = new Complex(0, 0);
		t.real = this.real * other.real - this.imaginary * other.imaginary;
		t.imaginary = this.real * other.imaginary + this.imaginary * other.real;
		return t;
	}

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

}