Java学生Vector数组无法打印姓名问题求助及代码修复

问题描述 #

我正在学习Java数组（题目中提及的Vector指此），练习时遇到问题：代码无法打印学生姓名字符串，不清楚原因。最终项目需求是打印平均分≥6的学生姓名，因姓名无法打印，我临时改为打印合格学生的平均分来验证功能，请帮忙修复？

现有代码 #

主类代码 #

package Program;

import java.util.Scanner;
import java.util.Locale;
import Entities.Student;

public class Program {

    public static void main(String[] args) {

        Locale.setDefault(Locale.US);
        Scanner sc = new Scanner(System.in);

        String name;
        double grade1;
        double grade2;
        double average;

        System.out.printf("how many students will you enter? ");
        int n = sc.nextInt();

        Student[] vect = new Student[n]; // 存储学生对象的数组

        for (int i = 0; i < vect.length; i++) {
            System.out.printf("imput the name, first and second grade for the student number %d%n ", i + 1);
            name = sc.nextLine(); // 读取姓名
            sc.nextLine();
            grade1 = sc.nextDouble();
            grade2 = sc.nextDouble();
            average = (grade1 + grade2) / 2;
            vect[i] = new Student(name, grade1, grade2, average);
        }

        for (int i = 0; i < vect.length; i++) {
            if (vect[i].getAverage() >= 6.0) {
                System.out.printf("%s%n", vect[i].getName());
                System.out.printf("%.2f%n", vect[i].getAverage());
            }
        }
    }
}

Student类代码 #

package Entities;

public class Student {
    private String name;
    private double grade1;
    private double grade2;
    private double average;

    public Student(String name, double grade1, double grade2, double average) {
        this.name = name;
        this.grade1 = grade1;
        this.grade2 = grade2;
        this.average = average;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public double getGrade1() {
        return grade1;
    }

    public void setGrade1(double grade1) {
        this.grade1 = grade1;
    }

    public double getGrade2() {
        return grade2;
    }

    public void setGrade2(double grade2) {
        this.grade2 = grade2;
    }

    public double getAverage() {
        return average;
    }

    public void setAverage(double average) {
        this.average = average;
    }

}

当前控制台输出 #

how many students will you enter? 5
imput the name, first and second grade for the student number 1
 John
10.0
9.0
imput the name, first and second grade for the student number 2
 Mary
5.0
4.5
imput the name, first and second grade for the student number 3
 Peter
8.5
9.5
imput the name, first and second grade for the student number 4
 Carl
9.9
7.5
imput the name, first and second grade for the student number 5
 Patricia
2.5
8.0

9.50

9.00

8.70

预期输出 #

John
9.5

Peter
9.0

Carl
8.70

问题分析与修复 #

核心问题 #

问题出在Scanner的输入缓冲区处理：

1. 调用sc.nextInt()读取学生数量后，输入缓冲区中残留了换行符，第一个sc.nextLine()会读取这个空换行符，导致name被赋值为空字符串。
2. 后续多余的sc.nextLine()会跳过用户实际输入的姓名，进一步导致所有学生姓名为空。

修复后的主类代码 #

package Program;

import java.util.Scanner;
import java.util.Locale;
import Entities.Student;

public class Program {

    public static void main(String[] args) {

        Locale.setDefault(Locale.US);
        Scanner sc = new Scanner(System.in);

        String name;
        double grade1;
        double grade2;
        double average;

        System.out.printf("how many students will you enter? ");
        int n = sc.nextInt();
        sc.nextLine(); // 读取nextInt()遗留的换行符，避免干扰后续输入

        Student[] vect = new Student[n];

        for (int i = 0; i < vect.length; i++) {
            System.out.printf("input the name, first and second grade for the student number %d%n", i + 1);
            name = sc.nextLine(); // 正确读取姓名
            grade1 = sc.nextDouble();
            grade2 = sc.nextDouble();
            sc.nextLine(); // 读取nextDouble()遗留的换行符，保证下一次循环的姓名读取正常
            average = (grade1 + grade2) / 2;
            vect[i] = new Student(name, grade1, grade2, average);
        }

        // 输出合格学生信息
        for (int i = 0; i < vect.length; i++) {
            if (vect[i].getAverage() >= 6.0) {
                System.out.printf("%s%n", vect[i].getName());
                System.out.printf("%.2f%n%n", vect[i].getAverage());
            }
        }
        sc.close(); // 关闭Scanner资源
    }
}

额外优化（可选） #

Student类中的average字段可以通过计算动态生成，无需存储，避免数据不一致问题：
修改后的Student类代码：

package Entities;

public class Student {
    private String name;
    private double grade1;
    private double grade2;

    public Student(String name, double grade1, double grade2) {
        this.name = name;
        this.grade1 = grade1;
        this.grade2 = grade2;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public double getGrade1() {
        return grade1;
    }

    public void setGrade1(double grade1) {
        this.grade1 = grade1;
    }

    public double getGrade2() {
        return grade2;
    }

    public void setGrade2(double grade2) {
        this.grade2 = grade2;
    }

    // 动态计算平均分
    public double getAverage() {
        return (grade1 + grade2) / 2;
    }
}

此时主类中创建Student对象的代码需改为：

vect[i] = new Student(name, grade1, grade2);

内容的提问来源于stack exchange，提问作者Laura