Abstract and array

[John Valiant]

Hi

My issue is i cant get the arrays correct,with abstract class.Can some one highlight to me the errors in class Example1.I want to create 2 extra pets (iguana & hamster) but i am getting it wrong.

below are the errors from my complier

23.java:37: error: constructor GoldFish in class GoldFish cannot be applied to given types;
owner.pets[2]=new GoldFish();
^
required: String
found: no arguments
reason: actual and formal argument lists differ in length
23.java:38: error: constructor Dog in class Dog cannot be applied to given types;
owner.pets[3]=new Dog("Hamster");
^
required: no arguments
found: String
reason: actual and formal argument lists differ in length
23.java:39: error: constructor Dog in class Dog cannot be applied to given types;
owner.pets[4]=new Dog("Iguana");
^
required: no arguments
found: String
reason: actual and formal argument lists differ in length
3 errors

abstract class Pet {

abstract void perform();
}

class Dog extends Pet {
void perform() { System.out.println("*The dog rolls over*"); }
}
class GoldFish extends Pet{
void perform() { 
System.out.println("*GoldFish eats alot*"); }
public String action="Blowing bubbles";
GoldFish(String action){
this.action = action;
}
public String getAction(){
return action;

}   
}
class Human {

String firstName = "Unknown";
String lastName = "Unknown";
Pet[] pets = new Pet[5]; 
void speak() { System.out.println("My name is " + firstName + " " + lastName); }
}
class Example1 {
public static void main(String[] args) {
    Human owner = new Human();
    owner.firstName="Andy";
    owner.lastName="Cole";
    owner.speak();
    owner.pets[0]=new Dog();
    owner.pets[1]=new Fish();
    owner.pets[2]=new GoldFish();
    owner.pets[3]=new Dog("Hamster");
    owner.pets[4]=new Dog("Iguana");

    System.out.println("My pets will perform the following tricks:");
    if (owner.pets != null) {
        for (int i = 0; i < owner.pets.length; i++) {
            Pet somePet = owner.pets[i];
            if (somePet != null) {
                somePet.perform();
            }
        }
    }

}

}

[Mohamed Sanaulla]

From what the error says- your Dog doesn't have a constructor which takes a String and the GoldFish class doesnt have a constructor which takes no arguments. So you need to be adding them.

[Winston Gutkowski]

John Valiant wrote:Can some one highlight to me the errors in class Example1.I want to create 2 extra pets (iguana & hamster) but i am getting it wrong.

Well, your Goldfish class has a contructor that takes a String, and your Dog class doesn't; yet you're trying to add a Dog with a String and a Goldfish without one.

Winston

[Edit] Too slow

[John Valiant]

ok thanks but how can this be solved then? should i be making changes to array in class example?

[John Valiant]

class Example1 {
	public static void main(String[] args) {
		Human owner = new Human();
		owner.firstName="Andy";
		owner.lastName="Cole";
		owner.speak();
		owner.pets[0]=new Dog();
		owner.pets[1]=new Fish();
		owner.pets[2]=new GoldFish();
		owner.pets[3]=new GoldFish("Hamster");
		owner.pets[4]=new GoldFish("Iguana");

This time 1 error....errrrr any idea how to solve this?

23.java:37: error: constructor GoldFish in class GoldFish cannot be applied to given types;
owner.pets[2]=new GoldFish();
^
required: String
found: no arguments
reason: actual and formal argument lists differ in length
1 error

[Mohamed Sanaulla]

owner.pets[2]=new GoldFish(); this line is using a constructor which is non existent in the GoldFish class. Either change this to pass a String or add a Default constructor to GoldFish class. Once you provide an overloaded constructor the compiler doesn't add the No-Args (default) constructor, so in such cases one has to provide the default constructor.

[John Valiant]

Thanks Mohammad, managed to get things running but a few queries(pardon my ignorance).
1.Why didnt the complier recognize the below code as a constructor?

GoldFish(String action){
	this.action = action;
	}

2.if i want to use the getAction() in ,let say, hamster,how can i go about doing that?

[Mohamed Sanaulla]

John Valiant wrote:Thanks Mohammad, managed to get things running but a few queries(pardon my ignorance).
1.Why didnt the complier recognize the below code as a constructor?

GoldFish(String action){
	this.action = action;
	}

It is recognised as a constructor. And that is why these lines owner.pets[3]=new GoldFish("Hamster"); and the other worked.

John Valiant wrote:2.if i want to use the getAction() in ,let say, hamster,how can i go about doing that?

if you mean invoking getAction() on owner.pets[3]=new GoldFish("Hamster"); then it would be owner.pets[3].getAction();

On a side note: please indent your code so that its more readable.

[John Valiant]

ok it worked only when i overloaded it.GoldFish(){
}

class GoldFish extends Pet{
	void perform() { 
	System.out.println("*GoldFish eats alot*"); }
	public String action="Blowing bubbles";
	GoldFish(){
	}
	GoldFish(String action){
	this.action = action;
	}
	public String getAction(){
	return this.action;

[Jeff Verdegan]

John Valiant wrote:ok it worked only when i overloaded it.GoldFish(){

Of course. That's what people have been telling you all along. You have this:

owner.pets[2]=new GoldFish();  
owner.pets[3]=new GoldFish("Hamster");  

So since you're calling both a no-arg Goldfish c'tor and a String-arg Goldfish c'tor, you need to define both a no-arg Goldfish c'tor and a String-arg Goldfish c'tor.

One of the rules of constructors that was mentioned above is: If you don't define any c'tors on your class, the compile inserts a no-arg c'tor that does nothing. But if you define one or more, then the compiler no longer inserts one.

If the no-arg Goldfish() {} c'tor doesn't exist--either from the compiler or from you--there's no way that first line can work.