Question

帮助！代码保持返回为“nullnull”！我试图这样做，如果我有多个元素，它将显示在控制台中。这更像是一个两部分问题...... 1.我将多个不同的元素符号保存到一个变量中，它不会工作吗？我应该如何制作它以便每次都保存在不同的变量下？ 2.为什么它一直作为nullnull返回？我认为应该将某些东西保存为元素1.虽然不太确定element11但是...... 谢谢你的帮助！

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);
        }
    }
}

Answer 1

在阅读element的输入后，您已将其分配给变量element1 null。

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

在BufferedWriter循环之外初始化while个实例。
如果您使用的是java 7，请使用try-with-resource语句自动为您关闭资源。

Answer 2

替换

element = element1;

与

element1 = element;

和

     element = element11;

带

     element11 = element;

然后将每个新单词附加到文本文件

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

Answer 3

从本质上讲，你有这个：

    String element1 = null;
    String element11 = null;

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

但是你设置的是element1和element11。结果应该是什么？“nullnull”应该是什么？

java中的文件写入和读取始终返回null

3 个答案: