我有2个文件Details.java和TestDetails.java以及一个名为Details.dat的数据文件
Details.java
import java.util.Scanner;
import java.io.*;
public class Details {
private String path;
File myFile = new File(path);
public void setMyFile(String path) {
this.path = path;
}
public void load() throws IOException, FileNotFoundException {
Scanner input = new Scanner(myFile);
int numberOfMembers = input.nextInt();
String[] members = new String[numberOfMembers];
for (String s : members) {
String name = input.next();
String age = input.next();
String qualification = input.next();
System.out.println("The name of the family member is " + name + " the age of the family member is" + age
+ " the qualification of the " + "family member is" + qualification);
}
}
}
TestDetails.java
import java.io.IOException;
public class TestDetails {
public static void main(String[] args) {
Details myDetails = new Details();
myDetails.setMyFile(args[0]);
try {
myDetails.load();
} catch (IOException i) {
System.out.println(i.getMessage());
}
}
}
Details.dat
4
a 26 bsc
b 22 bcom
c 50 ba
d 60 bsc
每当我尝试运行TestDetails.java文件时,我都会收到NullPointerException,堆栈跟踪将堆栈跟踪指向File对象。
那么这里有什么问题?为什么我得到NullPointerException?
在setFile()方法argumnet中的p.s,我在命令提示符的args [0]位置传入Details.dat
答案 0 :(得分:3)
问题在于:
public class Details{
private String path;
File myFile = new File(path);
...
构造对象时将执行File myFile = new File(path)
行。这意味着执行此行时path
为空。
您应该更改代码,以便仅在需要时实例化File
对象。
答案 1 :(得分:3)
首先初始化文件,然后设置文件路径。 尝试在Details类中使用构造函数:
public Details(String path)
this.path = path;
myFile = new File(path);
}
答案 2 :(得分:0)
public class Details{
private String path;
File myFile =new File(path);
...
myFile
如何将其路径设置为除""
以外的任何其他内容?
答案 3 :(得分:0)
您正在尝试使用路径名创建File对象而不初始化路径。因为
File myFile = new File(path);
行将在设置路径之前执行,并且此时它为空。所以先设置path的值,然后创建File的对象。