Question

我正在尝试将多个联系人编写并保存到一个文件中，然后将其存储为Hex文件，但它会不断创建多个文件（每个联系人一个）。我试图移动：

  System.out.print("Type a name for this file, followed by hitting 'enter': ");
    String fName = kbReader.nextLine();

    //append information to the string to be converted
    utfString = name + "\r\n" + pNumber + "\r\n" + fact;

    //outputs variables to file in hexadecimal format
    PrintStream fileStream = new PrintStream(fName);
    fileStream.println(toHex(utfString));

部分到While循环，它会在用户说没有更多联系人添加到文件后创建文件。我想用这段代码获取的路径是每个联系人都以Hex代码的形式写入文件，然后用户说他们想要输入另一个联系人，所以程序在第一个联系人之后立即将新联系人写入Hex文件之一。

代码：

 import java.util.Scanner;
 import java.io.PrintStream;
 import java.io.IOException;

public class Exercise27{

public static String toHex(String currString){

    //converts a string to a byte-array
    byte[] preConvert = currString.getBytes();

    //converts byte-array to hexadecimal string using a function from the javax library included in Java Platform SE 7 and onwards
    return javax.xml.bind.DatatypeConverter.printHexBinary(preConvert);

}

public static void main(String[] args) throws IOException{

    //starts keyboard input
    Scanner kbReader = new Scanner(System.in);
    Boolean MoreContacts = true;
    String More;
    do{

    //declare variable to convert to hex later on
    String utfString = "";

    //create variables for user-information
    System.out.print("Type your full name, followed by hitting 'enter': ");
    String name = kbReader.nextLine();
    System.out.print("Type your phone number, followed by hitting 'enter': ");
    String pNumber = kbReader.nextLine();
    System.out.print("Type one interesting fact about yourself, followed by hitting 'enter': ");
    String fact = kbReader.nextLine();
    System.out.print("Type a name for this file, followed by hitting 'enter': ");
    String fName = kbReader.nextLine();

    //append information to the string to be converted
    utfString = name + "\r\n" + pNumber + "\r\n" + fact;

    //outputs variables to file in hexadecimal format
    PrintStream fileStream = new PrintStream(fName);
    fileStream.println(toHex(utfString));

    System.out.println("More contacts? (Enter y or n)");
    MoreContacts = false;
    More = kbReader.nextLine();
    System.out.println("More: " + More);
    if((More.equalsIgnoreCase("y")) || (More.equalsIgnoreCase("yes")))
    {
      MoreContacts = true; 
    }

    }while(MoreContacts);



    PrintStream fileStream;

    //close your systems
    //fileStream.close();
    kbReader.close();

}

}

Answer 1

如果您想为联系人使用相同的文件，那么您真的应该只询问一次文件名。可能在这种情况下，在while循环之前。

所以在循环之前移动线：

System.out.print("Type a name for this file, followed by hitting 'enter': ");
String fName = kbReader.nextLine();

然后我建议您使用FileWriter，然后您可以选择附加到该文件。

File yourFile = new File(fName);
FileWriter fw = new FileWriter(yourFile, true);

然后在循环中，您可以使用

写入此内容

fw.write(toHex(utfString));

但是这不包括newlinw，所以你可能还需要添加

fw.write("\r\n");

然后不要忘记在写完所有数据后关闭作家

fw.close();

Answer 2

问题是在循环内部创建了PrintStream导致文件被截断，如PrintStream构造函数javadoc中所述：

参数：

file - 用作此打印目标的文件   流。如果文件存在，那么它将被截断为零大小;   否则，将创建一个新文件。输出将被写入   该文件并被缓冲。

您可以尝试：

import java.util.Scanner;
import java.io.PrintStream;
import java.io.IOException;

public class Exercise27{

public static String toHex(String currString){

//converts a string to a byte-array
byte[] preConvert = currString.getBytes();

//converts byte-array to hexadecimal string using a function from the javax library included in Java Platform SE 7 and onwards
return javax.xml.bind.DatatypeConverter.printHexBinary(preConvert);

}

public static void main(String[] args) throws IOException{

//starts keyboard input
Scanner kbReader = new Scanner(System.in);
System.out.print("Type a name for this file, followed by hitting 'enter': ");
String fName = kbReader.nextLine();
PrintStream fileStream = new PrintStream(fName);
Boolean MoreContacts = true;
String More;
do{

//declare variable to convert to hex later on
String utfString = "";

//create variables for user-information
System.out.print("Type your full name, followed by hitting 'enter': ");
String name = kbReader.nextLine();
System.out.print("Type your phone number, followed by hitting 'enter': ");
String pNumber = kbReader.nextLine();
System.out.print("Type one interesting fact about yourself, followed by hitting 'enter': ");
String fact = kbReader.nextLine();


//append information to the string to be converted
utfString = name + "\r\n" + pNumber + "\r\n" + fact;

//outputs variables to file in hexadecimal 
fileStream.println(toHex(utfString));

System.out.println("More contacts? (Enter y or n)");
MoreContacts = false;
More = kbReader.nextLine();
System.out.println("More: " + More);
if((More.equalsIgnoreCase("y")) || (More.equalsIgnoreCase("yes")))
{
  MoreContacts = true; 
}

}while(MoreContacts);



PrintStream fileStream;

//close your systems
//fileStream.close();
kbReader.close();

}

}

Java I / O：如何将循环输出打印到一个文件？

2 个答案: