你可以使用泛型来解决它。我认为这称为“好奇地重复通用模式”
将基类构建器方法的返回类型设为通用参数。
public class NutritionFacts {
private final int calories;
public static class Builder<T extends Builder<T>> {
private int calories = 0;
public Builder() {}
public T calories(int val) {
calories = val;
return (T) this;
}
public NutritionFacts build() { return new NutritionFacts(this); }
}
protected NutritionFacts(Builder<?> builder) {
calories = builder.calories;
}
}
现在使用派生的类构建器作为通用参数实例化基本构建器。
public class GMOFacts extends NutritionFacts {
private final boolean hasGMO;
public static class Builder extends NutritionFacts.Builder<Builder> {
private boolean hasGMO = false;
public Builder() {}
public Builder GMO(boolean val) {
hasGMO = val;
return this;
}
public GMOFacts build() { return new GMOFacts(this); }
}
protected GMOFacts(Builder builder) {
super(builder);
hasGMO = builder.hasGMO;
}
}
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