Item 02: Consider a builder when faced with many constructor parameters
Builder pattern
- Good for designing classes whose constructors or static factories would have more than a handful of parameters.
- Better to start with a builder in the first place to avoid obsolete constructors or static factories.
public class NutritionFacts {
public static class Builder {
// required parameters
// ...
// optional parameters - initialized to default values
// ...
// builder methods
public NutritionFacts build() {
return new NutritionFacts(this);
}
}
// builder constructor
private NutritionFacts(Builder builder) {
// set up parameters
}
}Builder for class hierarchies
Simulated self-type idiom: the self() method provides a workaround for the fact that Java lacks a self type.
public abstract class Pizza {
abstract static class Builder<T extends Builder<T>> {
abstract Pizza build();
// self-type idiom
protected abstract T self();
}
Pizza(Builder<?> builder) {
// set up parameters
}
}