使用变量类名而不是许多if子句？

Question

I'm trapped right now and don't know an easier solution to this, maybe you can help me out.

I have an Interface called Animal and lots of Animal Classes implementing it. EDIT: The interface must be wrong then:

public interface Animals {
    Integer lifespan = 0;

    public Integer getLifespan();
} 

In a function I get some random animal Object back and I want to get variables of it.

if (animal instanceof GuineaPig) {
            lifespan = ((GuineaPig) animal).getLifespan();
            age = ((GuineaPig) animal).getAge();
            value = ((GuineaPig) animal).getValue();
}
if (animal instanceof Rabbit) {
            lifespan = ((Rabbit) animal).getLifespan();
            age = ((Rabbit) animal).getAge();
            value = ((Rabbit) animal).getValue();
}

Now I need to have if clauses for every animal, there must be an easier way, right? What am I doing wrong?

EDIT2: Full Interface and Classes:

public interface Animals {
final Integer id = 0;
Integer prize = 999999;
Integer value = 0;
Integer age = 0;
Integer lifespan = 0;


String[] colors = {
        "c_bw", "c_w", "c_brw"
};


String name = null;
String finalColor = null;


public String[] getColors();
public Integer getPrize();
public Integer getId();
public Integer getLifespan();
public Integer getAge();
public Integer getValue();
public String getName();
public String setName(String animalName);
public String setFinalColor(String finalColor);
}

class GuineaPig implements Animals {
private final Integer id = 0;
private Integer prize = 10;
private final Integer difficulty = 0; // easy
private final Integer licenceNeeded = 0;
private Integer value = 5;
private Integer age = 0;


private String[] colors = {
    "c_bw", "c_w", "c_brw"
};


private String name = null;
private String finalColor = null;

@Override
public Integer getPrize() {
    return prize;
}


public void setPrize(Integer prize) {
    this.prize = prize;
}

public Integer getDifficulty() {
    return difficulty;
}

public Integer getLicenceNeeded() {
    return licenceNeeded;
}
@Override
public String[] getColors() {
    return colors;
}

public Integer getId() {
    return id;
}

@Override
public Integer getLifespan() {
    return null;
}

public String getName() {
    return name;
}

public String setName(String name) {
    this.name = name;
    return name;
}

public String getFinalColor() {
    return finalColor;
}

public String setFinalColor(String finalColor) {
    this.finalColor = finalColor;
    return finalColor;
}

public Integer getValue() {
    return value;
}

public void setValue(Integer value) {
    this.value = value;
}

public Integer getAge() {
    return age;
}

public void setAge(Integer age) {
    this.age = age;
}
}

class Rabbit implements Animals {
private final Integer id = 1;
private Integer prize = 15;
private Integer lifespan = 30;
private Integer difficulty = 0; // easy
private final Integer licenceNeeded = 1;
private Integer value = 7;
private Integer age = 0;


private String[] colors = {
        "c_b", "c_w", "c_br"
};


private String name = null;
private String finalColor = null;

@Override
public Integer getPrize() {
    return prize;
}

public void setPrize(Integer prize) {
    this.prize = prize;
}

public Integer getDifficulty() {
    return difficulty;
}

public Integer getLicenceNeeded() {
    return licenceNeeded;
}
@Override
public String[] getColors() {
    return colors;
}

public Integer getId() {
    return id;
}

@Override
public Integer getLifespan() {
    return null;
}

public String getName() {
    return name;
}

public String setName(String name) {
    this.name = name;
    return name;
}

public String getFinalColor() {
    return finalColor;
}

public String setFinalColor(String finalColor) {
    this.finalColor = finalColor;
    return finalColor;
}

public Integer getValue() {
    return value;
}

public void setValue(Integer value) {
    this.value = value;
}

public Integer getAge() {
    return age;
}

public void setAge(Integer age) {
    this.age = age;
}
}

Answer 1

In your small code sample, you can simply let the Animals interface have getLifespan() , getAge() and getValue() methods, and avoid the casting and the if statements :

lifespan = animal.getLifespan();
age = animal.getAge();
value = animal.getValue();

You didn't show the definition of your interface, but based on your question, it's possible that the Animal interface already has all those methods.

EDIT :

Your Animals interface (BTW Animal would be a better name) only defines getLifespan() . If you add the other methods to it (assuming all the classes that implement this interface have these methods), you'll be able to call them without casting.

Answer 2

You are not trapped. You overlooked at your problem.

Since Animal is an Interface, you need not to cast them to respected Instance types. Just removing all the conditions and writing

        lifespan = animal.getLifespan();
        age = animal.getAge();
        value = animal.getValue();

That should work as you are doing programming with interfaces. No need to add conditions at all.

Answer 3

Just use abstraction:

abstract class Animal {
    abstract int getAge();
    abstract int getValue();
...
}

And implements this methods in Rabbit(etc) classes or you can implement them in Animal class and just extend it.

Answer 4

you should declare getLifespan(), getAge() and getValue() methods in Animal interface. And then can use this:

Animal animal = new Rabbit(); //for example. Can change to new GuineaPig()
lifespan = animal.getLifespan();
age = animal.getAge();
value = animal.getValue();

Answer 5

I found the problem. It wasn't the Interface at fault or the classes...

Apparently I used a raw ArrayAdapter instead of a generic one. With a generic adapter it let me use the methods... I don`t even understand why, but whatever...