CODEWITHSUNDEEP
javainterface
cheifing
cheifing

Reputation: 25

Returning something that is equal to nothing in an interface

I have been making a Tetris-like game in Java recently, I have a interface IBlocks which goes over ConsBlock and EmptyBlock (ConsBlock is a list with a block at the beginnning and a IBlock list at the end, for some reason that's the way my teacher wanted it).

I have the getfirst() function in the interface:

public interface IBlocks{
//returns the first block in a list of blocks
public Resting getfirst();

(A Resting is one block in the Game)

Then, in the ConsBlock class, I have:

public class ConsBlock implements IBlocks{
//returns the first block in a list of blocks
public Resting getfirst(){
    return this.first;

But in the EmptyBlock class, I want it to return something that would be similar to saying there isn't one. I tried returning null, but that gave me a null pointer exception due to that fact that the function in the interface tells it to return a Resting. What would be the best way to represent an empty one without returning a Resting with random numbers?

Upvotes: 0

Views: 70

Answers (2)

durron597
durron597

Reputation: 32323

public interface IResting;
public class Resting implements IResting;

Then

public class EmptyResting implements IResting {
    @Override
    public Object sampleMethod() {
        // return what an empty block ought to return
    }
}

Further reading: http://en.wikipedia.org/wiki/Null_Object_pattern

Response to your comment: you still need to do:

public class EmptyBlock implements IBlocks {
    @Override
    public IResting getFirst() {
        return new EmptyResting();
    }
}

Note that your IBlocks and ConsBlock classes need to return an IResting not a Resting

Make sure to read that wiki link!

Upvotes: 1

D_Jones
D_Jones

Reputation: 16

I could be off-base with this but, I believe with your method header it is asking to have a Resting returned. Is there any way you can create a boolean object and have that returned? maybe name it something like empty and if it is empty it returns true and if it is not empty it returns false? Another suggestion would be to manually set Resting to 0 if it meets the criteria for being set to zero such as if (condition is met) { returnedResting = 0; }.

Upvotes: 0

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