如何摆脱这个Builder实现中的instanceof

public interface Builder {
    public Object build();
}

public class ConcreteBuilder1 implements Builder {
    public Object build() {
        // 实现Builder1的build()方法
    }
}

public class ConcreteBuilder2 implements Builder {
    public Object build() {
        // 实现Builder2的build()方法
    }
}

public class Director {
    private Builder builder;

    public Director(Builder builder) {
        this.builder = builder;
    }

    public Object construct() {
        return builder.build();
    }
}