如何解决Java的新手，试图解决OldMacdonald的练习的主要部分Had Farm歌曲
我正在尝试使用多态性对歌曲进行编码，但是我对Java编码非常陌生，并且具有非常基础的经验。我可以在类上使用一些帮助，但是我最大的问题是我不知道如何编写代码的主要部分，如果有人可以帮助我，我将非常感激。
这是我到目前为止的
public class OldMacdonald {
public interface Farm{
public String getName();
public String getNoise();
}
class Dog implements Farm{
String name;
String noise;
public Dog(String name,String noise) {
name=name;
noise=noise;
}
public String getName() {
return name;
}
public String getNoise() {
return noise;
}
}
class Cat implements Farm{
String name;
String noise;
public Cat(String name,String noise) {
name=name;
noise=noise;
}
public String getName() {
return name;
}
public String getNoise() {
return noise;
}
}
class Duck implements Farm{
String name;
String noise;
public Duck(String name,String noise) {
name=name;
noise=noise;
}
public String getName() {
return name;
}
public String getNoise() {
return noise;
}
}
class Cow implements Farm{
String name;
String noise;
public Cow(String name,String noise) {
name=name;
noise=noise;
}
public String getName() {
return name;
}
public String getNoise() {
return noise;
}
}
class Pig implements Farm{
String name;
String noise;
public Pig(String name,String noise) {
name=name;
noise=noise;
}
public String getName() {
return name;
}
public String getNoise() {
return noise;
}
}
class Song{
private Farm [] animal = new Farm[5];
Song() {
animal[0] = new Dog("dog","woof");
animal[1] = new Cat("cat","meow");
animal[2] = new Duck("duck","quack");
animal[3] = new Cow("cow","moo");
animal[4] = new Pig("pig","oink");
}
public void lyrics() {
int i;
for(i=0; i<animal.length; i++) {
System.out.println("Old MacDonald had a farm,E I E I O,\r\n" +
"And on his farm he had a " + animal[i].getName() + ",E I E I O.\r\n" +
"With a " + animal[i].getNoise() + " " + animal[i].getNoise() + " here and a " + animal[i].getNoise() + " " + animal[i].getNoise() + " there,\r\n" +
"Here a " + animal[i].getNoise() + ",there a " + animal[i].getNoise() + ",evrywhere a " + animal[i].getNoise() + " " + animal[i].getNoise() + ".\r\n" +
"Old MacDonald had a farm,E I E I O.\r\n\r\n");
}
}
}
public static void main(String[] args) {
// TODO Auto-generated method stub
}
}
解决方法
您需要在Java独立程序中以某种方式“启动”您的代码，这可以通过main方法完成：
_idSong似乎是您的课程，它实际上开始了所有事情，因此您需要创建一个实例：
public static void main(String[] args)
歌词是通过lyrics（）方法输出的，因此我们需要调用它：
public static void main(String[] args) {
Song mySong = new Song();
}
您也将要调整Song（）构造函数方法：
public static void main(String[] args) {
Song mySong = new Song();
mySong.lyrics();
}
您可能还想更新动物类中的构造函数，您正在为其分配参数（在params和private字段中对变量使用相同名称时很容易做到）：
public Song() {
如果我对您的理解正确，那么在您的main()方法中，您只需要创建Song的实例并对其调用lyrics()，不是吗？这样会将动物填充到Farm数组中，并在打印歌词时调用适当的方法。
您的代码存在三个问题：
- 您不需要声明类
OldMacdonald中的所有接口和类。 - 您尚未将任何参数值分配给实例变量，例如您需要使用
this.name = name来将参数name的值分配给实例变量name。 - 您需要实例化类
Song以便在实例上调用方法lyrics。
以下是包含这些注释的代码：
Farm.java：
public interface Farm {
public String getName();
public String getNoise();
}
OldMacdonald.java：
class Dog implements Farm {
String name;
String noise;
public Dog(String name,String noise) {
this.name = name;
this.noise = noise;
}
public String getName() {
return name;
}
public String getNoise() {
return noise;
}
}
class Cat implements Farm {
String name;
String noise;
public Cat(String name,String noise) {
this.name = name;
this.noise = noise;
}
public String getName() {
return name;
}
public String getNoise() {
return noise;
}
}
class Duck implements Farm {
String name;
String noise;
public Duck(String name,String noise) {
this.name = name;
this.noise = noise;
}
public String getName() {
return name;
}
public String getNoise() {
return noise;
}
}
class Cow implements Farm {
String name;
String noise;
public Cow(String name,String noise) {
this.name = name;
this.noise = noise;
}
public String getName() {
return name;
}
public String getNoise() {
return noise;
}
}
class Pig implements Farm {
String name;
String noise;
public Pig(String name,String noise) {
this.name = name;
this.noise = noise;
}
public String getName() {
return name;
}
public String getNoise() {
return noise;
}
}
class Song {
private Farm[] animal = new Farm[5];
Song() {
animal[0] = new Dog("dog","woof");
animal[1] = new Cat("cat","meow");
animal[2] = new Duck("duck","quack");
animal[3] = new Cow("cow","moo");
animal[4] = new Pig("pig","oink");
}
public void lyrics() {
int i;
for (i = 0; i < animal.length; i++) {
System.out.println("Old MacDonald had a farm,E I E I O,\r\n" + "And on his farm he had a "
+ animal[i].getName() + ",E I E I O.\r\n" + "With a " + animal[i].getNoise() + " "
+ animal[i].getNoise() + " here and a " + animal[i].getNoise() + " " + animal[i].getNoise()
+ " there,\r\n" + "Here a " + animal[i].getNoise() + ",there a " + animal[i].getNoise()
+ ",evrywhere a " + animal[i].getNoise() + " " + animal[i].getNoise() + ".\r\n"
+ "Old MacDonald had a farm,E I E I O.\r\n\r\n");
}
}
}
public class OldMacdonald {
public static void main(String[] args) {
new Song().lyrics();
}
}
输出：
Old MacDonald had a farm,And on his farm he had a dog,E I E I O.
With a woof woof here and a woof woof there,Here a woof,there a woof,evrywhere a woof woof.
Old MacDonald had a farm,E I E I O.
Old MacDonald had a farm,And on his farm he had a cat,E I E I O.
With a meow meow here and a meow meow there,Here a meow,there a meow,evrywhere a meow meow.
Old MacDonald had a farm,And on his farm he had a duck,E I E I O.
With a quack quack here and a quack quack there,Here a quack,there a quack,evrywhere a quack quack.
Old MacDonald had a farm,And on his farm he had a cow,E I E I O.
With a moo moo here and a moo moo there,Here a moo,there a moo,evrywhere a moo moo.
Old MacDonald had a farm,And on his farm he had a pig,E I E I O.
With a oink oink here and a oink oink there,Here a oink,there a oink,evrywhere a oink oink.
Old MacDonald had a farm,E I E I O.
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