为何向ArrayList添加一个对象后while循环提前终止？

问题根源 #

使用scanner.nextInt()读取节目时长后，输入缓冲区中会残留一个换行符（由按下回车产生）。当下一次循环执行scanner.nextLine()读取节目名称时，会直接读取到这个空的换行符，触发programName.isEmpty()的判断，导致循环提前终止。

修复方案 #

有两种简单的修复方式：

方式一：消耗残留的换行符

在调用scanner.nextInt()后，额外调用一次scanner.nextLine()来清空输入缓冲区里的换行符：

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

public class Main {

    public static void main(String[] args) {
        ArrayList<TelevisionProgram> programs = new ArrayList<>();
        Scanner scanner = new Scanner(System.in);

        while (true) {
            System.out.print("Name: ");
            String programName = scanner.nextLine();
            if (programName.isEmpty()) {
                break;
            }
            System.out.print("Duration: ");
            int durationOfProgram = scanner.nextInt();
            // 消耗掉nextInt()后残留的换行符
            scanner.nextLine();
            programs.add(new TelevisionProgram(programName, durationOfProgram));
        }
        System.out.println();
        System.out.print("Program's maximum duration? ");
        int maxDuration = scanner.nextInt();
        for (TelevisionProgram show : programs) {
            if (show.getDuration() <= maxDuration) {
                System.out.println(show);
            }
        }
    }
}

方式二：统一使用nextLine()读取输入

所有输入都用scanner.nextLine()读取，再将时长的字符串转换为整数，避免缓冲区残留问题：

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

public class Main {

    public static void main(String[] args) {
        ArrayList<TelevisionProgram> programs = new ArrayList<>();
        Scanner scanner = new Scanner(System.in);

        while (true) {
            System.out.print("Name: ");
            String programName = scanner.nextLine();
            if (programName.isEmpty()) {
                break;
            }
            System.out.print("Duration: ");
            // 读取整行后转换为整数
            int durationOfProgram = Integer.parseInt(scanner.nextLine());
            programs.add(new TelevisionProgram(programName, durationOfProgram));
        }
        System.out.println();
        System.out.print("Program's maximum duration? ");
        int maxDuration = Integer.parseInt(scanner.nextLine());
        for (TelevisionProgram show : programs) {
            if (show.getDuration() <= maxDuration) {
                System.out.println(show);
            }
        }
    }
}

内容的提问来源于stack exchange，提问作者Alex Roman