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当我尝试测试运行时,我不断得到第51行的空例外: songs [i] .title = Recording.setTitle(); 该方法似乎被称为罚款,那么为什么不是歌曲[我]。标题被设置? 我很新的导航类,所以请原谅,如果这是一个愚蠢的问题。这个错误的含义是什么:java.lang.NullPointerException
import java.util.Scanner;
class Recording {
String title;
String artist;
String time;
String getTitle(){
return title;
}
String getArtist(){
return artist;
}
String getTime(){
return time;
}
static String setTitle(){
Scanner title_input = new Scanner(System.in);
System.out.println("What is the title of your recording?");
String title_received = title_input.nextLine();
return title_received;
}
String setArtist(){
Scanner artist_input = new Scanner(System.in);
System.out.println("Who is the artist of your recording?");
String artist_received = artist_input.nextLine();
return artist_received;
}
String setTime(){
Scanner time_input = new Scanner(System.in);
System.out.println("How long is your recording of your recording?");
String time_received = time_input.nextLine();
return time_received;
}
}
public class RecordingSort {
public static void main(String[] args) {
Recording[] songs = new Recording[5];
for(int i = 0; i<5; ++i){
songs[i].title=Recording.setTitle();
System.out.println(songs[i].title);
}
}
}
的关键是,一个*参考*阵列最初充满空值。可以认为它与创建一个蛋盒相似。直到您首先用鸡蛋填充纸箱后才能使用任何鸡蛋。因此,例如对于您的歌曲数组,首先需要将录制对象分配给数组中的每个项目,然后才能调用它们的方法。 – 2015-04-03 21:52:40