常用的java应用程序，有杨辉三角，一元二次方程运算，复数运算

package javaapplication21; public class Complex { private double real; private double imaginary; public Complex(double a, double b){ this.real = a ; this.imaginary = b; }//构造方法 public Complex add(Complex a){ Complex result= new Complex(this.real+a.real,this.imaginary+a.imaginary); return result; } public Complex decrease(Complex a){ Complex result= new Complex(this.real-a.real,this.imaginary-a.imaginary); return result; } public Complex multiply(Complex a){ Complex result =new Complex(this.real*a.real-this.imaginary*a.imaginary, this.real*a.imaginary+this.imaginary*a.real); return result; } public String toString(){ String ComplexResult=new String(this.real+"+"+this.imaginary+"i"); return ComplexResult; } public static void main(String args[]){ Complex x=new Complex(5.2,3.0); Complex y=new Complex(3.0,4.0); System.out.println((x.add(y)).toString()); System.out.println((x.decrease(y)).toString()); System.out.println((x.multiply(y)).toString()); }}