Question

这个java代码哪里不对啊 Exception in thread "main" java.lang.NumberFormatException: null at java.la

import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;

//
public class IOLianXi
{

public static void main(String qrgs [] ) {
try{ BufferedReader inputStream = new BufferedReader(new FileReader("data.txt"));
String temp = null;
double sum = 0;
int count = 0;
int max = Integer.MIN_VALUE,min = Integer.MAX_VALUE;
while((temp = inputStream.readLine())!=null);{
int num = Integer.parseInt(temp);
if(num > max) {
max = num;
}
if(num < min) {
min = num;
sum += num;
count++;
}
}
System.out.println("max ="+max);
System.out.println("min ="+min);
System.out.println("Average ="+sum/count);
PrintWriter outputStream = new PrintWriter(new FileWriter("result.txt"));
outputStream.println(max);
outputStream.println(min);
outputStream.println(sum/count);
outputStream.close();
inputStream.close();
}catch(FileNotFoundException e) {
e.printStackTrace();

}catch(IOException e) {
e.printStackTrace();
}
}

}

最后报错
Exception in thread "main" java.lang.NumberFormatException: null
at java.lang.Integer.parseInt(Integer.java:415)
at java.lang.Integer.parseInt(Integer.java:497)
at ch01.IOLianXi.main(IOLianXi.java:21)

Answer 1

while((temp = inputStream.readLine())!=null);{

改为：

while((temp = inputStream.readLine())!=null){

多了一个“；”号啊

import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;
//
public class IOLianXi {
    public static void main(String qrgs[]) {
        try {
            BufferedReader inputStream = new BufferedReader(new FileReader(
                    "data.txt"));
            String temp = null;
            double sum = 0;
            int count = 0;
            int max = Integer.MIN_VALUE, min = Integer.MAX_VALUE;
            while ((temp = inputStream.readLine()) != null)
            {
                int num = Integer.parseInt(temp);
                if (num > max) {
                    max = num;
                }
                if (num < min) {
                    min = num;
                    sum += num;
                    count++;
                }
            }
            System.out.println("max =" + max);
            System.out.println("min =" + min);
            System.out.println("Average =" + sum / count);
            PrintWriter outputStream = new PrintWriter(new FileWriter(
                    "result.txt"));
            outputStream.println(max);
            outputStream.println(min);
            outputStream.println(sum / count);
            outputStream.close();
            inputStream.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}