JAVA中求一个复数加减乘除的运算
我编写了一个程序如下：
public class Complex 
{ 
private double realPart; 
private double imaginaryPart; 

public Complex(double a, double b) 
{ 
this.realPart = a; 
this.imaginaryPart = b; 
} 

public Complex add(Complex a) 
{                            //第13行   
    double newReal=this.realPart + a.realPart;
    double newImaginaryPart=this.imaginaryPart + a.imaginaryPart; 

if(newImaginaryPart>=0){
System.out.println("和为："+newReal+"+"+newImaginaryPart+"i");}
        else 
  System.out.println("和为："+newReal+"+"+"("+newImaginaryPart+")"+"i");

} 

public Complex decrease(Complex a) 
{                                   //第25行  
    double newReal=this.realPart - a.realPart;
    double newImaginaryPart=this.imaginaryPart - a.imaginaryPart; 
 
if(newImaginaryPart>=0){
System.out.println("差为："+newReal+"+"+newImaginaryPart+"i");}
        else 
  System.out.println("差为："+newReal+"+"+"("+newImaginaryPart+")"+"i");

} 

public Complex multiply(Complex a) 
{                                    //第37行  
double newReal=this.realPart*a.realPart - this.imaginaryPart * a.imaginaryPart; 
double newImaginaryPart=this.realPart*a.imaginaryPart + this.imaginaryPart * a.realPart; 

if(newImaginaryPart>=0){
System.out.println("积为："+newReal+"+"+newImaginaryPart+"i");}
        else 
  System.out.println("积为："+newReal+"+"+"("+newImaginaryPart+")"+"i");

} 

public Complex divide(Complex a) 
{                              //第49行  
    double newReal=(this.realPart*a.realPart+a.imaginaryPart*this.imaginaryPart)/(a.realPart*a.realPart+a.imaginaryPart*a.imaginaryPart);
    double newImaginaryPart=(this.imaginaryPart*a.realPart-this.realPart*a.imaginaryPart)/(a.realPart*a.realPart+a.imaginaryPart*a.imaginaryPart); 

if(newImaginaryPart>=0){
System.out.println("商为："+newReal+"+"+newImaginaryPart+"i");}
        else 
  System.out.println("商为："+newReal+"+"+"("+newImaginaryPart+")"+"i");

} 

public static void main(String [] args) 
{ 
Complex a = new Complex (2,3); 
Complex b = new Complex (1,1); 
a.add(b);
a.decrease(b);
a.multiply(b);
a.divide(b);
} 
};
但是在javac Complex.java时他提示13 25 37 49行缺少返回语句。
请教高手帮忙啊！！！先谢谢了。