Question

非常新的java，并想知道为什么即使扫描器的输入为“N”，这个while语句也不会结束，从而将表达式计算为false。

import java.util.*;

public class addSongs {

    public static void main (String[]args){

        Scanner songAdd = new Scanner(System.in);
        Scanner addContinue = new Scanner(System.in);
        String ceaseAdd = new String();
        ceaseAdd = "Y";

        while(ceaseAdd != "N")
            System.out.println("Enter track title");
            String newSong = songAdd.nextLine();
            MP3_catalogue.title.add(newSong);
            System.out.println("Enter artist name");
            String newArtist = songAdd.nextLine();
            MP3_catalogue.artist.add(newArtist);
            System.out.println("Enter duration");
            String newDuration = songAdd.nextLine();
            MP3_catalogue.duration.add(newDuration);
            System.out.println("Would you like to add another song? Y/N");
            ceaseAdd = addContinue.nextLine().toUpperCase();
    }

}

Answer 1

除了已经指出的字符串检查。遗失{}。正确缩进代码如下所示：

while(ceaseAdd != "N")
    System.out.println("Enter track title");
String newSong = songAdd.nextLine();
MP3_catalogue.title.add(newSong);
System.out.println("Enter artist name");

没有{} while仅适用于第一行。它应该是这样的：

while(!ceaseAdd.equals("N")){      
    System.out.println("Enter track title");
    String newSong = songAdd.nextLine();
    MP3_catalogue.title.add(newSong);
    System.out.println("Enter artist name");
    String newArtist = songAdd.nextLine();
    MP3_catalogue.artist.add(newArtist);
    System.out.println("Enter duration");
    String newDuration = songAdd.nextLine();
    MP3_catalogue.duration.add(newDuration);
    System.out.println("Would you like to add another song? Y/N");
    ceaseAdd = addContinue.nextLine().toUpperCase();
}

Answer 2

在java中，你不要将字符串与“==”进行比较。 “==”检查它是否是完全相同的对象，如果它具有相同的值则不会。要检查它是否具有相同的文本，您必须使用

string.equals()

在您的示例中，它看起来像这样：

public static void main (String[]args){

Scanner songAdd = new Scanner(System.in);
Scanner addContinue = new Scanner(System.in);
String ceaseAdd = new String();
ceaseAdd = "Y";

while(!ceaseAdd.equals("N"))
    System.out.println("Enter track title");
    String newSong = songAdd.nextLine();
    MP3_catalogue.title.add(newSong);
    System.out.println("Enter artist name");
    String newArtist = songAdd.nextLine();
    MP3_catalogue.artist.add(newArtist);
    System.out.println("Enter duration");
    String newDuration = songAdd.nextLine();
    MP3_catalogue.duration.add(newDuration);
    System.out.println("Would you like to add another song? Y/N");
    ceaseAdd = addContinue.nextLine().toUpperCase();
}

尽管错误的评估，仍然继续循环扫描仪表达

2 个答案: