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

遵循本教程的“带有字符串的管道”部分： http : //www.jonathanbeard.io/tutorials/CtoJava

我想修改StreamTest代码，以便可以将数据保存到变量中并将其传递给另一个类。

我尝试这样做（请参阅下文），但是当我运行java -cp时。 从教程的StreamTest我得到这个：

在类StreamTest中找不到主要方法，请将该主要方法定义为：public static void main（String [] args）

我猜这是有道理的，但是我现在仍然对如何解决这个问题感到困惑。

主要思想是我希望能够从c代码中获取数据，将其放入变量传递（我想通过StreamTest代码），然后将该变量传递给我的mainLaptop类

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;

}
}

这是我想将数据传递到的主要类

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);*/
}
}

这是未修改的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: "+sb.toString());
        bis.close();
    }
    catch(IOException ex)
    {

    }

    finally
    {


    }

  //  mainLaptop.main(pass);

}

这是C代码

#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;
}

这是make文件

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

ap.text文件只是一堆数字

我已经更新了StreamTest代码并通过Eclipse运行它，但是我的输出是

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

代替

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

更新了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

一切都错了...您正在跑步

java -cp

因此，这是尝试运行您的应用程序的错误，因此它无法找到Main方法，因为Java在尝试运行应用程序时会查找Main方法。

如果要保存数据，只需将数据传递到命令中，如下所示

java -cp。 类“您想要的字符串”

然后在main方法中，您需要从“ String args []”中读取它：)

EDITED

@Jas Buddy你在做什么??? 你怎么有两个主要的方法....？ 废弃StreamTest仅使用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);*/
}
}

如果您从eclipse运行它，请右键单击运行->运行配置->参数

输出将是“ teenagemutant”，因为我们仅采用了args [0]，如果您需要其他值，则arg 1 ，args 2 ...

如果您想在命令行上运行它