java中的文件写入和读取始终返回为空

-1

帮助！代码不断返回为“nullnull”！我试图让它如此，如果我有多个元素，它会将它显示到控制台中。这是更多的两部分问题... 1.我将多个不同的元素符号保存到一个变量，它不会工作吗？我应该如何做到这一点，以便每次都保存在不同的变量下？ 2.为什么它会继续返回nullnull？我认为东西应该被保存为元素1.不是很确定element11，但... 感谢您的帮助！java中的文件写入和读取始终返回为空

import java.io.BufferedWriter; 
import java.io.DataInputStream; 
import java.io.FileInputStream; 
import java.io.FileWriter; 
import java.io.IOException; 
import java.io.Writer; 

import javax.swing.JOptionPane; 

public class Science1 { 

    @SuppressWarnings("deprecation") 
    public static void main(String[] args) throws IOException { 
     // TODO Auto-generated method stub 
     String element; 
     int more; 
     FileInputStream fin; 
     JOptionPane.showMessageDialog(null, "Balancing chemical equations, capable for anything with more than one compound"); 
     element = JOptionPane.showInputDialog("Please input an element"); 
     String element1 = null; 
     element = element1; 
     String element11 = null; 
     //MORE VARIABLES? 
     more = JOptionPane.showConfirmDialog(null, "Do you have more elements on this side?", element, JOptionPane.YES_NO_OPTION); 
     while(more == 0){ 
      element = JOptionPane.showInputDialog("Please input an element"); 

      element = element11; 
      Writer writer = null; 
      try { 
       writer = new BufferedWriter(new FileWriter("test.txt")); 
       writer.write(element1 + element11); 
      } catch (IOException e) { 
       e.printStackTrace(); 
      } finally { 
       if (writer != null) try { writer.close(); } catch (IOException ignore) {} 
      } 
      //MORE VARIABLES? 
      more = JOptionPane.showConfirmDialog(null, "Do you have more elements on this side?", element, JOptionPane.YES_NO_OPTION); 
     } 
     try 
     { 
      // Open an input stream 
      fin = new FileInputStream ("test.txt"); 

      // Read a line of text 
      System.out.println(new DataInputStream(fin).readLine()); 

      // Close our input stream 
      fin.close();   
     } 
     // Catches any error conditions 
     catch (IOException e) 
     { 
      System.err.println ("Unable to read from file"); 
      System.exit(-1); 
     } 
    } 
}

来源

2013-11-24 user3027609

读取输入到element后，已经将它分配给一个变量element1这是null。

element = JOptionPane.showInputDialog("Please input an element"); 
String element1 = null; //<<-----remove 
element = element1; //<<-----remove

初始化你BufferedWriter实例while循环之外。
如果您使用的是java 7，则使用try-with-resource语句，该语句将自动关闭您的资源。

来源

2013-11-24 16:14:18 Sage

取代

element = element1;

与

element1 = element;

和

 element = element11;

与

 element11 = element;

那么每个新词追加到文本文件

try { 
    PrintWriter writer = new PrintWriter(new BufferedWriter(new FileWriter("test.txt", true))); 
    writer.println(element11); 
    writer.close(); 
    } catch (IOException e) { 
    //! 
    }

来源

2013-11-24 16:14:28 iShaalan

你，在本质上，这一点：

String element1 = null; 
    String element11 = null; 

    while(more == 0){ 
     try { 
      writer = new BufferedWriter(new FileWriter("test.txt")); 
      writer.write(element1 + element11);

但你设置部件1和element11行不通的。结果是什么？“nullnull”应该是什么结果？

来源

2013-11-24 16:16:00 Ingo

java中的文件写入和读取始终返回为空

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