我试图在步骤6中返回创建的狗。
对于第6步，返回创建的狗只是
return selected_dog;
还是其他什么？因为selected_dog返回错误
这是DogTest类
import java.util.Scanner;
public class DogsTest
{
private static Scanner input = new Scanner(System.in);
public static void main(String[] args)
{
final String YES = "y";
String answer;
Dog my_dog; // Step 1
do
{
// ------------------------------------------------------------
// The compiler cannot know at compile time what type my_dog is
// so it is determined at runtime every time the loop iterates
// ------------------------------------------------------------
my_dog = getDog();
System.out.println(my_dog.getName() + " says " + my_dog.speak());
System.out.print("Try again? ");
answer = input.next();
} while (answer.equalsIgnoreCase(YES));
}
public static Dog getDog() // Step 2
{
int choice;
Dog selected_dog; // Step 3
String name,
color;
do
{
// ----------------------------------
// A null reference indicates that an
// invalid menu choice was entered
// ----------------------------------
selected_dog = null;
System.out.print("Choose a Breed (1. Labrador 2. Yorkshire): ");
choice = input.nextInt();
switch (choice)
{
case 1: System.out.print("Enter dog's name: ");
name = input.next();
System.out.print("Enter dog's color: ");
color = input.next();
selected_dog = Labrador; // Step 4
break;
case 2: System.out.print("Enter dog's name: ");
name = input.next();
selected_dog = ______; // Step 5
break;
default: System.out.println("Invalid choice");
break;
}
} while (selected_dog == null);
return __________________; // Step 6
}
}
狗班
public class Dog
{
protected String name;
public Dog(String name)
{
this.name = name;
}
public String getName()
{
return name;
}
public String speak()
{
return "Woof";
}
}
拉布拉多班
public class Labrador extends Dog
{
private String color;
private static int breed_weight = 75;
public Labrador(String name, String color)
{
this.color = color;
}
// =========================================
// Big bark -- overrides speak method in Dog
// =========================================
public String speak()
{
return "WOOF";
}
public static int avgBreedWeight()
{
return breed_weight;
}
}
答案 0 :(得分：1)
在您已经显示的第一行代码中，您尝试使用＆＃34;默认构造函数＆＃34;创建三个对象。那些课程。它会工作，但你错过了括号。它应该是这样的：
selected_dog = new Labrador();
但是，在你的狗和拉布拉多阶级，除了聋人之外你还有其他建设者。因此，如果您想创建具有特定名称和颜色的新拉布拉多，您应该这样写：
selected_dog = new Labrador("name", "color");
最后一件事。在labrador的构造函数中，您将名称作为参数传递但不使用它。您应该向该构造函数的第一行添加对超类构造函数的调用，如下所示：
public Labrador(String name, String color)
{
super(name);
this.color = color;
}
我希望我足够清楚:) 快乐学习！
<强>重新编辑：
看一下这段代码并尝试理解它：
DogsTest课程：
public class DogsTest {
private static final Scanner INPUT = new Scanner(System.in);
/**
* @param args the command line arguments
*/
public static void main(String[] args) {
final String YES = "y";
final String NO = "n";
String answer;
Dog my_dog; // Step 1
do {
// ------------------------------------------------------------
// The compiler cannot know at compile time what type my_dog is
// so it is determined at runtime every time the loop iterates
// ------------------------------------------------------------
my_dog = getDog();
System.out.println(my_dog.getName() + " says " + my_dog.speak());
do {
System.out.print("Try again? ");
answer = INPUT.next();
} while ( !( answer.equalsIgnoreCase(YES) || answer.equalsIgnoreCase(NO) ) );
} while (answer.equalsIgnoreCase(YES));
}
public static Dog getDog() {
int choice;
String name;
String color;
boolean loop = true;
do {
System.out.print("Choose a Breed (1. Labrador 2. Yorkshire) 3. Cancel: ");
choice = INPUT.nextInt();
switch (choice) {
case 1:
System.out.print("Enter dog's name: ");
name = INPUT.next();
System.out.print("Enter dog's color: ");
color = INPUT.next();
return new Labrador(name, color);
case 2:
System.out.print("Enter dog's name: ");
name = INPUT.next();
System.out.print("Enter dog's color: ");
color = INPUT.next();
return new Yorkshire(name, color);
case 3:
loop = false;
break;
default:
System.out.println("Invalid choice");
break;
}
} while (loop);
return null;
}
}
狗班：
public class Dog {
// ====================================================================================================
// DATA STRUCTURE
// Instance data
private String name;
// Class data
private static final String DEFAULT_NAME = "No name";
// ====================================================================================================
// CONTRUCTORS
// Complete
public Dog(String name) {
this.name = name;
}
// Default
public Dog() {
this.name = DEFAULT_NAME;
}
// Copy
public Dog(Dog dogToCopy) {
this.name = dogToCopy.name;
}
// ====================================================================================================
// GET
public String getName() {
return name;
}
// ====================================================================================================
// SET
public void setName(String name) {
this.name = name;
}
// ====================================================================================================
// TO STRING
@Override
public String toString() {
return "The dog's name is "+name+". ";
}
// ====================================================================================================
// FUNCTIONALITIES
public String speak() {
return "woof";
}
// ====================================================================================================
}
拉布拉多班：
public class Labrador extends Dog{
// ====================================================================================================
// DATA STRUCTURE
// Instance data
private String color;
// Class data
private static int breedWeight = 75;
private static final String DEFAULT_COLOR = "No color";
// ====================================================================================================
// CONTRUCTORS
// Complete
public Labrador(String name, String color) {
super(name);
this.color = color;
}
// Incomplete
public Labrador(String name) {
super(name);
}
// Default
public Labrador() {
super();
this.color = DEFAULT_COLOR;
}
// Copy
public Labrador(Labrador labradorToCopy) {
super(labradorToCopy.getName());
this.color = labradorToCopy.color;
}
// ====================================================================================================
// GET
public String getColor() {
return color;
}
// ====================================================================================================
// SET
public void setColor(String color) {
this.color = color;
}
public static void setBreedWeight(int newBreedWeight) {
Labrador.breedWeight = newBreedWeight;
}
// ====================================================================================================
// TO STRING
@Override
public String toString() {
return super.toString()+"The dog's color is "+color+". ";
}
// ====================================================================================================
// FUNCTIONALITIES
@Override
public String speak() {
return "WOOF";
}
public static int avgBreedWeight() {
return breedWeight;
}
// ====================================================================================================
}
约克郡班：
public class Yorkshire extends Dog {
// ====================================================================================================
// DATA STRUCTURE
// Instance data
private String color;
// Class data
private static int breedWeight = 75;
private static final String DEFAULT_COLOR = "No color";
// ====================================================================================================
// CONTRUCTORS
// Complete
public Yorkshire(String name, String color) {
super(name);
this.color = color;
}
// Incomplete
public Yorkshire(String name) {
super(name);
}
// Default
public Yorkshire() {
super();
this.color = DEFAULT_COLOR;
}
// Copy
public Yorkshire(Yorkshire yorkshireToCopy) {
super(yorkshireToCopy.getName());
this.color = yorkshireToCopy.color;
}
// ====================================================================================================
// GET
public String getColor() {
return color;
}
// ====================================================================================================
// SET
public void setColor(String color) {
this.color = color;
}
public static void setBreedWeight(int newBreedWeight) {
Yorkshire.breedWeight = newBreedWeight;
}
// ====================================================================================================
// TO STRING
@Override
public String toString() {
return super.toString()+"The dog's color is "+color+". ";
}
// ====================================================================================================
// FUNCTIONALITIES
@Override
public String speak() {
return "WOOF";
}
public static int avgBreedWeight() {
return breedWeight;
}
// ====================================================================================================
}
你能理解我做了什么吗？ 注意它的方式，如果你不在狗类型选择上写一个int，应用程序可能会崩溃。有办法防止这种情况;）
答案 1 :(得分：0)
好像你忘了输入正确
selected_dog = new Labrador("Bingo", "White");
Doe解决了你的问题？