java - 最终打印语句返回 null (java)

Question

我有一个基本的名称应用程序，它从主类中获取用户数据，在解析器类中拆分数据，然后尝试分配最终类中的所有内容并在 toString 方法中将其打印出来。我知道主类和解析器工作正常。我已经在解析器类中验证了数据确实正确分割，并且还通过我创建的对象将数据发送到最终类以将其全部分配。但是，我的最终代码返回 null..

主类

<小时/>

            import java.util.Scanner;
            public class MainClass {
                public static void main (String[]args)
                {
                    Scanner input = new Scanner(System.in); //create scanner object to gather name information
                    String fullName = null; //set the predefined value for the users name to null
                    nameParse splitInformation = new nameParse(); //method build to split the name into different sections
                    SecondClass access = new SecondClass(); //class built to output the different name data

                    System.out.println("What is your name?");

                    fullName = input.nextLine(); //store the users name and pass it into the data parser

                    splitInformation.parseNameInformation(fullName); //name parsing parameters built

                    System.out.println(access.toString());





                }

            }

数据解析器类

<小时/>

            public class nameParse {
                private String firstName;
                private String middleName;
                private String lastName;

                public nameParse()
                {
                    firstName = "initial";
                    middleName = "initial";
                    lastName = "initial";
                }

                public void parseNameInformation(String inputInfo)
                {

                    //Create an array to store the data and split it into multiple sectors
                    String nameInformation[] = inputInfo.split("\\s");

                    firstName = nameInformation[0];
                    middleName = nameInformation[1];
                    lastName = nameInformation[2];

                    //System.out.println(firstName + " " + middleName + " " + lastName);

                    SecondClass sendData = new SecondClass();

                    sendData.setFirstName(firstName);
                    sendData.setMiddleName(middleName);
                    sendData.setLastName(lastName);


                }

            }

最后一个类__

    public class SecondClass {

        private String firstName;
        private String middleName;
        private String lastName;


        /*public String GFN()
        {
            return firstName;
        }

        public String GMN()
        {
            return middleName;
        }

        public String GLN()
        {
            return lastName;
        }*/
        public String setFirstName(String yourFirstName)
        {
            firstName = yourFirstName;
            return this.firstName;
        }

        public String setMiddleName(String yourMiddleName)
        {
            middleName = yourMiddleName;
            return this.middleName;
        }

        public String setLastName(String yourLastName)
        {
            lastName = yourLastName;
            return this.lastName;
        }

        public String getFN()
        {
            return firstName;
        }

        public String toString()
        {
            String printNameInfo = "\nYour First Name:\t" + getFN();
            return printNameInfo;
        }

    }

Answer 1

您从未设置任何 SecondClass 对象的(称为“访问”)字段，因此它们当然都将为空。

简而言之，您的代码创建一个 nameParse 对象，从用户获取信息，但对该信息不执行任何操作。您创建了一个名为 access 的 SecondClass 对象，没有向其中放入任何数据，因此当您尝试打印它时，应该期望其中没有有效数据。解决方案:首先将信息放入 SecondClass 对象中。调用它的setter方法:

// be sure to call the setter methods before trying to print anything out:
access.setSomething(something);
access.setSomethingElse(somethingElse);

<小时/>

编辑
您声明:

I thought I set the data using the sendData.setFirstname(...) etc?

在 parseNameInformation 方法中，您创建了一个新的 SecondClass 对象，并设置了该对象的字段，但该对象与 main 方法中的字段仍然为 null 的对象完全不同。要解决此问题，请为 parseNameInformation 提供一个方法参数，并将主方法的 SecondClass 对象传入其中并设置其方法。当然，您必须在调用方法之前创建 SecondClass 对象。

即，

public void parseNameInformation(String inputInfo, SecondClass sendData)
{
    //Create an array to store the data and split it into multiple sectors
    String nameInformation[] = inputInfo.split("\\s");

    firstName = nameInformation[0];
    middleName = nameInformation[1];
    lastName = nameInformation[2];

    //System.out.println(firstName + " " + middleName + " " + lastName);

    // SecondClass sendData = new SecondClass();  // !!! get rid of this

    sendData.setFirstName(firstName);
    sendData.setMiddleName(middleName);
    sendData.setLastName(lastName);
}