Question

我试图制作一个可以接收三种不同数据输入的程序。第一个学生编号，第二个A标记，第三个B标记。输入数据后，程序将再次循环并询问第一个输入（学号），依此类推。一旦用户输入了所需的数据集，他们就可以通过在第一个输入（学号）上输入0来打破循环，因为这标志着一组新数据的开始。

我如何打印出用户输入的多个数据集？

这是输入和输出的外观：

节目输入：

Student Number: --> 12345678
A Mark: --> 30
B Mark: --> 60
Student Number: --> 62445677
A Mark: --> 40
B Mark: --> 70
Student Number: --> 0

预期产出：

sn = 12345678 B = 60 A = 30 mark = 33.0
sn = 62445677 B = 70 A = 40 mark = 33.0

到目前为止，只能打印出1个数据集：

import java.util.Scanner;
import java.util.*;
public class test
{
    public static void main (String[] args) {
        Scanner reader = new Scanner(System.in);

        // 0 To end the loop and run output! Repeats until 0 is entered!
        // Arraylist for each of the Vars!
        // Validation

        // Have to initialise - 1 So it doesn't terminate
        int studentNumber = 1;
        int studentNumberPassed = 12;

        int aMark = 0;
        int bMark = 0;

        int markTotal;
        double markAverage;

        boolean terminate = false;


        while (terminate == false) {
            studentNumber = reader.nextInt();
            if (studentNumber == 0) {
                terminate = true;
                break;
            }
            // Once 0 is inputted to terminate it overwrites.
            studentNumberPassed = studentNumber;
            aMark = reader.nextInt();
            bMark = reader.nextInt();
        }

        markTotal = aMark +  bMark;
        // Cast to double before calculating
        markAverage = (double) markTotal / 2;

        //Can also use out.format
        System.out.printf("sn = %d ex = %d cw = %d mark = %.1f",
            studentNumberPassed, aMark, bMark, markAverage);
    }
}

Answer 1

说明

目前，您在每次迭代中覆盖字段studentNumberPassed，examMark和cwMark 。这也是为什么最后只保存最后一个阅读学生的数据，因此你只输出最后一个学生。

解决方案

您需要将数据存储在某种集合中。或者，您可以直接输出数据，同时迭代。

对于集合，Java中有Collection（documentation）接口，子类别为List（documentation）和Set（{{3} }）（等等）。 List可以满足您的需求，例如LinkedList（documentation）。

容器

这样的集合包含对象。您需要一些容器对象来保存学生的所有数据。我们先设计一下这个容器类：

public class StudentData {
    // Member variables for all data
    public int mStudentNumber;
    public int mCwMark;
    public int mExamMark;

    // A constructor setting all data
    public StudentData(int studentNumber, int cwMark, int examMark) {
        // Pass the data to the members variables
        this.mStudentNumber = studentNumber;
        this.mCwMark = cwMark;
        this.mExamMark = examMark;
    }
}

请注意，对于良好的设计，我们会使用成员变量private并使用getter方法进行访问。但为了简单起见，我们就放弃了。

收集数据

现在我们构建LinkedList并收集所有数据：

// Create an empty list
final LinkedList<StudentData> dataList = new LinkedList<>();

// Iterate and collect
while (terminate == false) {
    studentNumber = reader.nextInt();
    if (studentNumber == 0) {
        terminate = true;
        break;
    }
    studentNumberPassed = studentNumber;
    cwMark = reader.nextInt();
    examMark = reader.nextInt();

    // Create container and pass values
    final StudentData studentData = new StudentData(studentNumberPassed, cwMark, examMark);

    // Add the container to the list
    dataList.add(studentData);
}

输出数据

现在剩下的就是迭代容器并输出数据：

// A "for-each" loop which elegantly iterates all elements in a collection
for (final StudentData studentData : dataList) {
    markTotal = studentData.mExamMark + studentData.mCwMark;
    markAverage = (double) markTotal / 2;

    System.out.printf("sn = %d ex = %d cw = %d mark = %.1f",
        studentData.mStudentNumber,
        studentData.mExamMark,
        studentData.mCwMark,
        markAverage);
}

Answer 2

输入多个数据集（输入），然后打印

它满足您的输入和输出结果，但是有很多方法可以实现多个数据集（输入）然后打印。

import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

public class Test {
    private static List<String> storeResult;
    public static void main(String[] args) {
        Scanner reader = new Scanner(System.in);
        // 0 To end the loop and run output! Repeats until 0 is entered!
        // Arraylist for each of the Vars!
        // Validation
        int studentNumber = 1; //Have to initialise - 1 So it doesn't terminate 
        int studentNumberPassed = 12;
        int cwMark = 0;
        int examMark = 0;

        boolean terminate = false;
        storeResult = new ArrayList<String>();
        while (terminate == false) {
            System.out.print("Student Number: --> ");
            studentNumber = reader.nextInt();
            if (studentNumber == 0) { // Once 0 is inputted to terminate it overwrites.
                terminate = true;
                displayResult();
                return;
            }

            studentNumberPassed = studentNumber; 
            System.out.print("CW Mark: --> ");
            cwMark = reader.nextInt();
            System.out.print("EX Mark: --> ");
            examMark = reader.nextInt();
            result(studentNumberPassed, cwMark, examMark);
        }
    }

    private static void result(int studentNumberPassed, int cwMark, int examMark) {
        int markTotal;
        double markAverage;
        markTotal = examMark + cwMark;
        // Cast to double before calculating
        markAverage = (double) markTotal / 2;
        String str = "sn = " + studentNumberPassed + " ex = " + examMark + " cw = " + cwMark + " mark = " + markAverage;
        storeResult.add(str);

    }

    private static void displayResult() {
        for(int data=0;data<storeResult.size();data++){
            System.out.println(""+storeResult.get(data));
        }
    }
}

输入多个数据集（输入）然后打印

2 个答案:

说明

解决方案

容器

收集数据

输出数据