内部与外部类的Builder模式？

Question

在类外使用构建器模式有什么好处？

课内:

public class Person {
    private String name;
    private String eyeColor;
    private String hairColor;

    public Person setName(String name) {
        this.name = name;
        return this;
    }

    public Person setEyeColor(String eyeColor) {
        this.eyeColor = eyeColor;
        return this;
    }

    public Person setHairColor(String hairColor) {
        this.hairColor = hairColor;
        return this;
    }
} 

// Example usage:
Person p = new Person()
                 .setName("Bob")
                 .setHairColor("Black")
                 .setEyeColor("Brown")

课外:

public class Person {
    private String name;
    private String eyeColor;
    private String hairColor;

    public Person(String name, String eyeColor, String hairColor) {
        this.name = name;
        this.eyeColor = eyeColor;
        this.hairColor = hairColor; 
    }  
} 

public class PersonBuilder {
    private String name;
    private String eyeColor;
    private String hairColor;

    public Person build() {
        return new Person(name, eyeColor, hairColor);
    }

    public PersonBuilder with(String name) {
        this.name = name;
        return this;
    }

    public PersonBuilder setEyeColor(String eyeColor) {
        this.eyeColor = eyeColor;
        return this;
    }

    public PersonBuilder setHairColor(String hairColor) {
        this.hairColor = hairColor;
        return this;
    }
} 

// Example usage:
Person p = new PersonBuilder()
                 .setName("Bob")
                 .setHairColor("Black")
                 .setEyeColor("Brown")
                 .build();

Answer 1

这取决于.

我经常组合Builder和Factory模式,因此将Builder作为外部类是有意义的,因为"构建"对象可能是许多实现之一.这有一个额外的好处,允许实现是包私有或甚至是Builder的私有内部类.

如果您正在使用Builder来使公共类的构造函数更具有意图,或者更加简洁,而不是真正的个人偏好.人们可以权衡在API中增加一个类的优缺点,这可能会让用户感到困惑.

但是,我建议选择其中一个选项并在整个API中坚持使用它.如果所有构建器都是内部类或外部类,它使整个系统架构更容易理解; 不要混合它们.

不要像这样混合内部和外部构建器:

Foo foo = new Foo.Builder(...)

Bar bar = new BarBuilder(...)