适应方法调用的Builder模式

问题描述

这是试图从有效Java第2版中了解第40项：小心设计方法签名的部分。

This is an attempt to understand a portion of ITEM 40: Design Method Signatures Carefully from Effective Java 2nd Edition.

建议改进方法签名可读性的事情是针对四个或更少的参数。建议使用多种技术来管理更长的参数列表，其中之一如下：

One of the things suggested to improve method signature readability is to aim for four or fewer parameters. It is suggested that longer parameter lists be managed by using a variety of techniques one of which is as follows :

我熟悉Builder模式，因为它用于对象构造，但不知道我是否已经正确地了解了如何使它适应于方法调用。

I am familiar with the Builder pattern as it is used for object construction, but am not sure whether I have correctly understood how to adapt it to method invocation.

这是我到目前为止：

（我已经尝试改进方法调用的 move 方法）

Here is what I have thus far :
( I have attempted to improve the method invocation for the move method)

public class Space {

    public static class Builder {
        // Required parameters
        private final int x;
        private final int y;
        private final int z;

        // optional params
        private long time = 0;

        public Builder(int x, int y, int z) {
            this.x = x;
            this.y = y;
            this.z = z;
        }

        public Builder time(long val) {
            time = val;
            return this;
        }

        public void move() {
            if (x == 0 || y == 0 || z == 0) {
                throw new IllegalArgumentException("Cannot move to the centre of the universe");
            }

            // Do the actual work here
        }
    }

//  public void move(int x, int y, int z, long time) {
//      // Do the work here
//  }

    public static void main(String[] args) {
        new Builder(1, 1, -1).time(1234).move();
    }
}

我对Joshua Bloch的建议的解释是否正确？ p>


Is my interpretation of Joshua Bloch's advice correct ?

推荐答案

我使用我想要实例化的类中定义的接口完成了Builder模式的验证。

I've done reifications of the Builder pattern using an interface defined inside the class I want to instantiate.

有关这个和相关的双向构建器的更多信息，请参阅这里：

See here for extra info on this and the related "bidirectional builder": http://www.javaworld.com/javaworld/jw-01-2004/jw-0102-toolbox.html?page=3

我会做如下的事情：虽然这对于3个必填字段可能是过分的，但是对于构建较大的对象而言，这对于每个必需字段都是非常有帮助的。

I would do something like the following; although this is overkill perhaps for 3 required fields, it is very helpful for constructing larger objects while accounting for every required field.

public Class Space
{
    public interface Builder
    {
        public Space build();
        public int x();
        public int y();
        public int z();
    }

    // Build a complete Space object accounting for every field.
    public Space(Space.Builder spaceBuilder)
    {
        this.x = spaceBuilder.x();
        this.y = spaceBuilder.y();
        this.z = spaceBuilder.z();
        this.time = builder.time();
    }

    // Might not be necessar if you update time when you update x, y, and z
     public Builder time(long val)
     {
            time = val;
            return this;
     }

     public void move()
     {
        // ...
     }

    public static void main(String[] args)
    {
        new Builder()
        {
            @Override
            public Space build(){ return new Space(this);}

            @Override
            public int x(){ return 1;}

            @Override
            public int y{ return 1;}

            @Override int z{ return -1;}
        }.build().time(1234).move();
    }
}

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