Java类：如何制作一个返回字符串参数但也可用作应用程序入口点的类？

Question

Following the "PIPE WITH STRINGS" section of this tutorial: http://www.jonathanbeard.io/tutorials/CtoJava

I want to modify the StreamTest code so that I can save the data to a variable and pass it to another class.

I tried doing that (See Below) but when I run java -cp . StreamTest from the tutorial I get this:

Main method not found in class StreamTest, please define the main method as: public static void main(String[] args)

Which makes sense I guess, but I am kind of stuck on how to approach this now.

The main idea is that I want to be able to get the data from the c code, put it in the variable pass (I guess through the StreamTest code), and then pass that variable to my mainLaptop class

import java.io.BufferedInputStream; 
import java.io.IOException;
import java.io.InputStream;

public class StreamTest
{
private static final int buffer = 4096;
public static String main(String [] args, String pass)
{

    InputStream is = null;
    BufferedInputStream bis = null;
    try
    {
        bis = new BufferedInputStream(System.in,buffer);
        StringBuilder sb = new StringBuilder();
        sb.append((char)bis.read());
        while(bis.available() > 0)
        {
            sb.append((char)bis.read());
        }

        System.out.println("JAVA SIDE: "+sb.toString());
        pass=sb.toString();
        bis.close();

    }
    catch(IOException ex){}
    finally{}
    //return pass;
    return pass;

}
}

Here is the main class I want to pass the data into

public class mainLaptop 
{

public static void main(String arg) throws Exception 
{   
    //Timing out? change the IP!
    String ip="192.168.137.127";
    String Pi1Q1="Leonardo";
    String Pi1Q2="Raphael";
    String Pi2Q3="Donatello";
    String Pi2Q4="Michelangelo";
    String pass=arg;
    //pass= StreamTest.main(pass);

    Send.send(ip, Pi1Q1, pass);
    Send.send(ip, Pi1Q2, pass);
    Send.send(ip, Pi2Q3, pass);
    Send.send(ip, Pi2Q4, pass);

/*  Recv.recv(ip, Pi1Q1);
    Recv.recv(ip, Pi1Q2);
    Recv.recv(ip, Pi2Q3);
    Recv.recv(ip, Pi2Q4);*/
}
}

Here is the unmodified StreamTest that works

import java.io.BufferedInputStream; 
import java.io.IOException;
import java.io.InputStream;

public class StreamTest
   {
    private static final int buffer = 4096;

   public static void main(String[] args) throws Exception 
  {   
    String pass=null;
    InputStream is = null;
    BufferedInputStream bis = null;
    try
    {
        bis = new BufferedInputStream(System.in,buffer);
        StringBuilder sb = new StringBuilder();
        //sb.append((char)bis.read());
        while(bis.available() > 0){
            sb.append((char)bis.read());
        }
        pass = sb.toString();
        System.out.println("JAVA SIDE: "+sb.toString());
        bis.close();
    }
    catch(IOException ex)
    {

    }

    finally
    {


    }

  //  mainLaptop.main(pass);

}

Here is the c code

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdint.h>
#include <inttypes.h>

#define DEBUG 0
#define BUFFER 4096

//open ap.txt for text input
static const char* exFile = "ap.txt";
static char inputBuffer[BUFFER];

int main(int argc, const char** argv)
{
   FILE *fp = fopen(exFile,"r");
   /*check and see if the pointer is null in otherwords see if the memory 
   location refered to by fp is set...no memory location should be zero 
   if you want to reference it   
   Here are some good ways to do this other than the way I did it below:
   if(!fp) {do error}
   if(fp == NULL) {do error}
   and then there's the way I did it below
   */

   if(fp == 0){
      fprintf(stderr,"Null pointer exception, check file name.\n");
      exit(-1);
   }

   //check and see if an error occured during open
   const int err = ferror(fp);
   if(err != 0){
      /*
     void perror(const char* err)
     returns specific error message to string attached.

     */
  const char* errMessage = strcat("Something bad happened while opening 
  file ",exFile);
  perror(errMessage);
   }
     #if (DEBUG == 1)   
    else
    {
      fprintf(stderr,"Success opening file!!\n");
    }  
    #endif




setbuf(fp,inputBuffer); //set a buffer for input

uint64_t *num = (uint64_t*) malloc(sizeof(uint64_t));
uint64_t total = 0;
uint64_t n = 0;

//test for eof
/*
feof(*fp) - returns a boolean true if at end of file and false otherwise
*/

while(!feof(fp)){
//fscanf returns the number of items it converted using %llu, if it's not 
 equal to 1 we don't want to continue
   if(fscanf(fp,"%"PRIu64"",num)!=1)
  break; //you could do a lot of stuff here as far as error handling but 
basically something bad has happened
   total+= *num; //add to total the value at memory location num
   n++;
    #if (DEBUG == 1)   
    fprintf(stderr,"line number %"PRIu64"\n",n);
    #endif 
    }

    free(num);

const double average = (double) total / (double) n;
//close the inputfile
fclose(fp);

//declare our outputfile, use a pipe in this case to a java process
//we open a java process for this process to pipe to, also it is 
//technically a bi-directional pipe so we can use any of the modifiers
//like r/w/r+/etc
static const char* outFile = "java -cp . StreamTest";

FILE *fp_out = popen(outFile,"w");
//setbuf(fp_out,outputBuffer);

fprintf(fp_out,"Total: %"PRIu64", Integers: %"PRIu64", Average: 
%.4f\n",total,n,average);



/*
int fflush(*fp) pushes any data in the buffer to be written
the return value returns 0 if successful or !=0 if an error 
occurs....remember return values in C often equal exceptions

*/   
   fflush(fp_out);

/*

int 

 */
    fclose(fp_out);

   return 1;
}

Here is the make file

CC ?=gcc
JCC ?= javac
FLAGS ?= -Wall -O2
JFLAGS ?= -g -verbose

all: c_app StreamTest

c_app: c_app.c
    $(CC) $(FLAGS) -o c_app c_app.c

StreamTest: StreamTest.java
    $(JCC) $(JFLAGS) StreamTest.java $(LIBS)

clean:
    rm -f c_app StreamTest.class

The ap.text file is just a bunch of numbers

I've updated my StreamTest code and run it through eclipse but my output is

JAVA SIDE: 
 [x] Sent ''Leonardo
 [x] Sent ''Raphael
 [x] Sent ''Donatello
 [x] Sent ''Michelangelo

instead of

JAVA SIDE: 
 [x] Sent 'Total: 4953, Integers: 1000, Average: 4.9530'Leonardo
 [x] Sent 'Total: 4953, Integers: 1000, Average: 4.9530'Raphael
 [x] Sent 'Total: 4953, Integers: 1000, Average: 4.9530'Donatello
 [x] Sent 'Total: 4953, Integers: 1000, Average: 4.9530'Michelangelo

Updated StreamTest

import java.io.BufferedInputStream; 
import java.io.IOException;
import java.io.InputStream;

public class StreamTest
{
private static final int buffer = 4096;

public static void main(String[] args) throws Exception 
{
    String pass=null;
    InputStream is = null;
    BufferedInputStream bis = null;
    try
    {
        bis = new BufferedInputStream(System.in,buffer);
        StringBuilder sb = new StringBuilder();
        //sb.append((char)bis.read());
        while(bis.available() > 0){
            sb.append((char)bis.read());
        }
        pass = sb.toString();
        System.out.println("JAVA SIDE: "+pass);
        bis.close();
    }
    catch(IOException ex)
    {

    }

    finally
    {


    }
    //pass = "hi";
    mainLaptop.main(pass);

}    
}

Answer 1

You've got it all wrong ... you are running

java -cp

So this is trying to run your application, hence the error, that it cant find a Main method because Java looks for a Main method when trying to run an application...

If you want to save the data just pass the data into the command like so

java -cp . class "the string you want"

And then in the main method you have the "String args[]" read it from that :)

EDITED

@Jas Buddy what are you doing ??? how can you have two main Method ....? scrap StreamTest use only mainLaptop ....

public class mainLaptop 
{

public static void main(String arg) throws Exception 
{   
    //Timing out? change the IP!
    String ip="192.168.137.127";
    String Pi1Q1="Leonardo";
    String Pi1Q2="Raphael";
    String Pi2Q3="Donatello";
    String Pi2Q4="Michelangelo";
    String pass=arg[0]; // reads the argument you pass from command line or eclipse
    //pass= StreamTest.main(pass);

    Send.send(ip, Pi1Q1, pass);
    Send.send(ip, Pi1Q2, pass);
    Send.send(ip, Pi2Q3, pass);
    Send.send(ip, Pi2Q4, pass);

/*  Recv.recv(ip, Pi1Q1);
    Recv.recv(ip, Pi1Q2);
    Recv.recv(ip, Pi2Q3);
    Recv.recv(ip, Pi2Q4);*/
}
}

IF you are running it from eclipse Right click run-->Run configuration--> Arguments

Output will be "teenagemutant" because we have taken only args[0], if you want the other values then arg 1 ,args 2 ...

if you want to run it on commandLine then