How to use a Builder for different length of input?

Question

I am using a Builder(pattern) to build and return an object. There is a defined order depending on the number of available arguments on how the methods should be called. Currently I use if-else blocks. Is there a java 8 or higher alternative to use the builder dynamically?

public Task createTask(String[] params){
    if(params.length < 1){
       throw new IllegalArgumentException();
    }
    else if(params.length == 1){
        return new TaskBuilder().setOne(params[0]).build();
    }
    else if(params.length == 2){
        return new TaskBuilder().setOne(params[0])
                                .setTwo(params[1]).build();
    }
    else if(params.length == 3){
        return new TaskBuilder().setOne(params[0])
                                .setTwo(params[1])
                                .setThree(params[2]).build();
    }
    else if(params.length == 4){
        return new TaskBuilder().setOne(params[0])
                                .setTwo(params[1])
                                .setThree(params[2])
                                .setFour(params[3]).build();

    }
    else if(params.length == 5){
        return new TaskBuilder().setOne(params[0])
                                .setTwo(params[1])
                                .setThree(params[2])
                                .setFour(params[3])
                                .setFive(params[4]).build();

    }
    else{
        throw new IllegalArgumentException();
    }

}

You could theoretically have an array of function references to "setOne", "setTwo", and so on, and then iterate over that. — , Aug 21 '20 at 18:53
@Taschi I don't know what you mean exactly. Could you add one or two sentences about how I can implement your approach or give me a suitable search term so I can google it by myself? — nopens, Aug 21 '20 at 19:00
Check out https://stackoverflow.com/questions/49234884/how-to-declare-an-array-of-method-references, there are some examples of what I have in mind. — , Aug 21 '20 at 19:11

score 3 · Accepted Answer · answered Aug 21 '20 at 19:26

You don't really need anything fancy like function references. All you have to do is break the builder calls up:

public Task createTask(String[] params){
    if (params.length < 1 || params.length > 5) {
        throw new IllegalArgumentException();
    }

    TaskBuilder builder = new TaskBuilder();

    if (params.length >= 1) { builder = builder.setOne(params[0]); }
    if (params.length >= 2) { builder = builder.setTwo(params[1]); }
    if (params.length >= 3) { builder = builder.setThree(params[2]); }
    if (params.length >= 4) { builder = builder.setFour(params[3]); }
    if (params.length >= 5) { builder = builder.setFive(params[4]); }
    
    return builder.build();
}

Missed the wood for the trees. Thank you very much. – nopens Aug 21 '20 at 21:16 — nopens, Aug 21 '20 at 21:16

How to use a Builder for different length of input?

1 Answers1