java 复数类。定义的四个 方法 声明无效需要返回类型。请各位大侠，前辈帮忙看看

Question

import java.util.Scanner;
import java.io.*;
public class ComplexNumber{
 private float real;        private float image;        public ComplexNumber(float a, float b)
        {         this.real=a;         this.image=b;         }

    public static String readString()
    {
        //从键盘读取字符串
        BufferedReader br=new BufferedReader(new InputStreamReader(System.in),1);
        String s1="";
        try{
            s1=br.readLine();
        }catch(IOException ex){
            System.out.println(ex);
       
        return s1;
        }
   }
    public static float readFloat(){
        //字符串转换为浮点数
        return Float.parseFloat(readString());
    }
    
    
    
    public ComplexNumber()
    {
     real=0.0;
     image=0.0;
    }
  
    public add(ComplexNumber c)
    {
     ComplexNumber result=new ComplexNumber(this.real+c.real,this.image+c.image);         return result;
    }
    public sub(ComplexNumber c)
    {
     ComplexNumber result=new ComplexNumber(this.real-c.real,this.image-c.image);
     return result;
    }
    public mul(ComplexNumber c)
    {
     ComplexNumber result=new ComplexNumber(this.real*c.real-this.image*c.image,                                      this.real*c.image+this.image*c.real);         return result;
    }
    public div(ComplexNumber c)
    {
     ComplexNumber result=new ComplexNumber((this.real*c.real+this.image*c.image)/(c.real*c.real+c.image*c.image),                                      (this.image*c.real+this.real*c.image)/(c.real*c.real+c.image*c.image));
          return result;
    }
    public String toString(){         String ComplexNunber=new String(this.real+"+"+this.imaginary+"i");         return ComplexNunber;      }
    }
  
public class void main()(String[] args )
    {
     ComplexNumber a=new ComplexNumber();
     ComplexNumber b=new ComplexNumber();
     System.out.println("Enter the first ComplexNumber");
    
     a.real=ComplexNumber.readFloat();
     a.image=ComplexNumber.readFloat();
     System.out.println("Enter the second ComplexNumber");
    
     b.real=ComplexNumber.readFloat();
     b.image=ComplexNumber.readFloat();
     System.out.println((a.add(b)).toString());        System.out.println((a.sub(b)).toString());        System.out.println((a.mul(b)).toString());     System.out.println((a.div(b)).toString());
     }
    
   

Answer 1

public sub(ComplexNumber c)   public ComplexNumber sub(...)

Answer 2

你都写了return result了为啥不设定返回值

Answer 3

还有，你的代码很多错误，"public class void main()(String[] args )”这是啥？

Answer 4

现在 改好了，还有一个问题    public static String readString()
   {
   //从键盘读取字符串
   BufferedReader br=new BufferedReader(new InputStreamReader(System.in),1);
   String s1="";
   try{
   s1=br.readLine();
   }catch(IOException ex){
   System.out.println(ex);
     
  return s1;
   }
   }
 这里 编译结果 提示 缺少返回语句。。