显示存储在HashMap中的对象值 [英] Displaying object values which are stored in a HashMap

问题描述

我有一个HashMap，其中存储了一个字符串(键)和一个Student对象(值).我希望遍历哈希并显示每个键/值对.但是，我要显示键，然后显示存储在Student对象中的字符串名称值.我尝试了几种方法，每种方法都以某种方式使我失败.我相信我不完全了解静态"修饰符，也不完全了解如何使用HashMaps.

I have a HashMap in which I have stored a string(key) and a Student object(value). I wish to iterate through the hash and display each key/value pair. However, I want to display the key followed by the String name value stored in the Student object. I have tried several ways and each one fails me in some way. I believe I do not entirely understand the "static" modifier, nor do I fully understand how to use HashMaps.

这是我的完整程序:

import java.io.*;
import java.util.Scanner;
import java.util.HashMap;
import java.util.Iterator;
public class FinalProgram {
    public static void main(String[] args) throws IOException {
        nameReader();
    }

    private static void nameReader() throws IOException {
        String nameFile = " ";
        String next = " ";
        int sNumber = 0;
        String formatSNumber = " ";
        String sName = " ";
        Scanner input = new Scanner(System.in);
        HashMap<String, Student> map = new HashMap<>();

        try {
            System.out.print("Enter the Name file(c:filename.txt): ");
            nameFile = input.nextLine();
        } catch(IllegalArgumentException e) {
            System.out.printf("Invalid input. Please enter"
                    + " filename in the form of "
                    + "c:filename.txt\n", e.getMessage());
        }
        //Instantiate FileReader and BufferedReader
        FileReader freader = new FileReader(nameFile);
        BufferedReader Breader = new BufferedReader(freader);
        boolean end = Breader.ready();

        do {
            next = Breader.readLine();
            sNumber = Integer.parseInt(next);
            formatSNumber = String.format("%03d", sNumber);
            sName = Breader.readLine();
            Student student = new Student(sName);
            map.put(formatSNumber, student);
            end = Breader.ready();
        } while(end);
        Iterator<String> keySetIterator = map.keySet().iterator();
        while(keySetIterator.hasNext()) {
            String key = keySetIterator.next();
            System.out.println("key: " + key + " value: " + map.get(Student.getName()));
        }
    }

这是我读取名称文件的算法:

This is my algorithm for reading the name file:

//Declaration of HashMap
HashMap<String, Student> map = new HashMap<>();

do {
            next = Breader.readLine();
            sNumber = Integer.parseInt(next);
            formatSNumber = String.format("%03d", sNumber);
            sName = Breader.readLine();
            Student student = new Student(sName);
            map.put(formatSNumber, student);
            end = Breader.ready();
        } while(end);
        Iterator<String> keySetIterator = map.keySet().iterator();
        while(keySetIterator.hasNext()) {
            String key = keySetIterator.next();
            System.out.println("key: " + key + " value: " +     map.get(key));
        }

这是我的学生类(由于遇到了问题，我将同时进行getter和setts并作成构造函数，

This is my Student class(I have done both getters and setts and made a constructor since I am having issues which I will explain next:

public class Student {
    private String name = " ";
    public Student(String name) {
        this.name = name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getName() {
        return name;
    }
    Course course = new Course();
}

现在，当我尝试使用以下方法遍历地图时:

Now, when I try to iterate through my map with:

while(keySetIterator.hasNext()) {
                String key = keySetIterator.next();
                System.out.println("key: " + key + " value: " +         map.get(key));
            }

输出为:

Enter the Name file(c:filename.txt): c:name.txt
key: 001 value: finalprogram.Student@5cbc508c
key: 002 value: finalprogram.Student@3419866c
key: 030 value: finalprogram.Student@63e31ee

它存储了完美的键，但是我无法显示它来显示Student对象的名称.我也尝试过静态变量，但是它返回null(我向Student类中的每个变量和方法都添加了"static"):

It stores the keys perfect, but I cannot get it to display the name of the Student object. I have tried static variables as well, but it returns null(I added 'static' to every variable and method in the Student class):

Enter the Name file(c:filename.txt): c:name.txt
key: 001 value: null
key: 002 value: null
key: 030 value: null

当我尝试直接调用它时:

and when I try to call it directly:

System.out.println("key: " + key + " value: " + map.get(Student.getName()));

我收到错误:

Non-static method getName() cannot be referenced rom a static context.

推荐答案

如果您没有为Student类提供toString()实现，它将打印您所看到的默认值.您可以覆盖toString().

If you don't provide a toString() implementation for your Student class, it prints the default which is what you are seeing. You can override toString().

public class Student {
    private String name = " ";
    public Student(String name) {
        this.name = name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getName() {
        return name;
    }
    Course course = new Course();

    public String toString() {
        return name;
    }

}

与Student.getName()一样，您正在尝试调用类的方法，而不是类的实例. Student.getName()是调用静态方法的方式.您想为非静态方法调用类似key.getName()之类的东西.

As for Student.getName(), you are attempting to call a method on a class and not an instance of a class. Student.getName() is how you call a static method. You want to call something like key.getName() for a non-static method.

但这实际上不是您的问题.正确的语法应为map.get(key).getName();

But that's not actually your problem. The correct syntax would be map.get(key).getName();

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