Java Main中的NullPointerException错误
当用户在控制台中输入文件名时，尝试读取文件。程序编译和运行时没有错误。输入文件名并按enter键后，将出现此错误。不知道为什么。任何帮助都将不胜感激Java Main中的NullPointerException错误,java,nullpointerexception,Java,Nullpointerexception,当用户在控制台中输入文件名时，尝试读取文件。程序编译和运行时没有错误。输入文件名并按enter键后，将出现此错误。不知道为什么。任何帮助都将不胜感激 Exception in thread "main" java.lang.NullPointerException at java.io.Writer.<init>(Writer.java:88) at java.io.PrintWriter.<init>(PrintWriter.java:113) at java.io.P
Exception in thread "main" java.lang.NullPointerException
at java.io.Writer.<init>(Writer.java:88)
at java.io.PrintWriter.<init>(PrintWriter.java:113)
at java.io.PrintWriter.<init>(PrintWriter.java:100)
at propertylistings.propertylistings.main(propertylistings.java:34)
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Scanner;
import java.util.Set;
import java.util.SortedMap;
import java.util.TreeMap;
import java.util.TreeSet;
public class propertylistings {
public static void main(String[] args)
throws FileNotFoundException
{
// Prompt for the input file name
Scanner console = new Scanner(System.in);
System.out.print("Input file: ");
String inputFileName = console.next();
BufferedWriter pwfo = null;
try {
pwfo = new BufferedWriter(new FileWriter("C:\\agentReport.txt",
true));
} catch (IOException e) {
}
//next line is LINE 34
PrintWriter pwo = new PrintWriter(pwfo);
// Construct property type treeSet
Set<String> propertyTypes = pTypes(inputFileName);
// Print property types from treeSet
for (String type : propertyTypes) {
System.out.println(type);
pwo.println(type);
}
// Construct agent ids and values treeSet
Set<String> agentRpt = agentValue(inputFileName);
// Print agent Ids and values from key set
for (String tail : agentRpt) {
{
System.out.println(tail);
pwo.println(tail);
}
}
pwo.flush();
pwo.close();
}
// Reads the input file.
// @return the alphabetized property types in uppercase.
public static Set<String> pTypes(String inputFileName)
throws FileNotFoundException
// Construct a tree set to return property types
{
Set<String> type = new TreeSet<String>();
Scanner in = new Scanner(new File(inputFileName));
// Use delimiters to select specific chars for set
in.useDelimiter("[1234567890. ]");
while (in.hasNext()) {
type.add(in.next().toUpperCase());
}
in.close();
return type;
}
// Reads the input file.
// @returns the Agent id's and corresponding property values.
public static Set<String> agentValue(String inputFileName)
throws FileNotFoundException {
TreeSet<String> tail = new TreeSet<String>();
SortedMap<String, Number> agentValues = new TreeMap<String, Number>();
Scanner in = new Scanner(new File(inputFileName));
String line = inputFileName;
while (in.hasNextLine()) {
try {
line = in.nextLine();
String[] fields = line.split("[\\s}]");
String agentId = (fields[3]);
Double pValue = Double.parseDouble(fields[2]);
if (agentValues.containsKey(agentId)) {
pValue += agentValues.get(agentId).doubleValue();
}
agentValues.put(agentId, pValue);
} catch (Exception e) {
}
// Create keyMap with all keys and values
Set<String> keySet = agentValues.keySet();
for (String key : keySet) {
Number value = agentValues.get(key);
// System.out.println(key + ":" + value);
tail.add(key + ":" + value);
}
}
return tail;
}
}
在catch块中放置stacktrace，您将知道确切的错误
try {
pwfo = new BufferedWriter(new FileWriter("C:\\agentReport.txt", true));
} catch (IOException e) {
e.printstacktrace();
}
catch（IOE异常）{}IOExceptionpwfonull