我有个书上的程序不明白是哪里有问题,是关于向上转型的;
有四个类文件;
(1)
package thinkinjava.c07;
class Instrument {
public void play(){}
static void tune(Instrument i){
i.play();
}
}
(2)
package thinkinjava.c07;
public class Wind extends Instrument {
public void play(Note n) {
System.out.println( "Wind.play() " + n);
}
}
(3)
package thinkinjava.c07;
public class Note {
private String noteName;
private Note(String noteName) {
this.noteName = noteName;
}
public String toString() {
return noteName;
}
public static final Note
MIDDLE_C = new Note( "Middle C "),
C_SHARP = new Note( "C Sharp "),
B_FLAT = new Note( "B Flat ");
}
(4)
package thinkinjava.c07;
public class Music {
public static void tune(Instrument i){
i.play(Note.MIDDLE_C); //这里提示i.play这行出错
}
public static void main(String[] agrs){
Wind flute = new Wind();
tune(flute);
}
}
在这里我把tune()方法里的参数改成Instrument的子类Wind就是正常的,可是这种向上转型在书上说是允许的,我不明白这是哪里错了为什么错了,所以请大家帮帮我
------解决方案--------------------
向上转型是允许的
------解决方案--------------------
Instrument 没有 play(Note.MIDDLE_C) 这个方法 只有public void play(){}