Question

我的代码出现问题。它编译，但我遇到了一个扫描仪打印null的问题多少次是由于我放置的驱动程序类末尾的for-each循环。目标是从文本文件中读取名字，姓氏和邮政编码字符串，并使用for-each循环打印输入。我不确定我做错了什么。

输入文件的示例行将读取如下内容：

名字：Joe姓：Jimbob邮政编码：55555

编辑：.txt文件中有25行代表一个包含25个Person对象的数组。我的坏！

这是我到目前为止简化的内容：

用于打印数据和驱动程序的驱动程序类：

... throws IO Exception

    String firstname = " ";
        String lastname = " ";
        String postalcode = " ";
        File file = new File("input.txt"); 
        Scanner fileScan = new Scanner(file);
        Person person[] = new Person[25]; // An array of 25 Person objects see Person class


        while(fileScan.hasNext()) //Error was generated here at Line 20 originally N. Pointer Exception not too sure how to regenerate it
        {
            String token= fileScan.next(); //Token to scan for each word and match it with the string before it
            if(token.equals("Firstname: "))
            {
                firstname = fileScan.next();
            }
            else if(token.equals("Lastname: "))
            {
                lastname = fileScan.next();
            }
            else if(token.equals("Postalcode: "))
            {
                postalcode = fileScan.next();
            }

            for(Person info : person)  // Generates null on execution supposed to print Array
            {
                System.out.println(info); // Prints null not exactly sure why 
            }

Person类可以看到Person对象的创建位置：

public class Person
{
    private String firstname, lastname, postalcode;

    public Person(String firstname, String lastname, String postalcode)
    {
        this.firstname = firstname;
        this.lastname = lastname;
        this.postalcode = postalcode;

    }

    public String toString()
    {
        return(firstname + " " + lastname +" "+ postalcode);
    }
}

Answer 1

关闭while循环后需要使用for循环。类似的东西：

while(fileScan.hasNext())
    {
        String token= fileScan.next();
        if(token.equals("Firstname: "))
        {
            firstname = fileScan.next();
        }
        else if(token.equals("Lastname: "))
        {
            lastname = fileScan.next();
        }
        else if(token.equals("Postalcode: "))
        {
            postalcode = fileScan.next();
        }
    }
    for(Person info : person)
    {
        System.out.println(info);
    }

如果文件中的人数少于25人，仍然会打印空值。您也可以尝试：

    for(Person info : person)
    {
        if(info != null){
            System.out.println(info);
        }
    }

编辑：

注意到它看起来好像你没有将人员添加到数组中？像

person[2] = new Person(firstName, lastname, postalcode); //etc

带有Array对象的FileScanner

1 个答案: