Builder方式创建对象

在创建对象需要初始化数据，数据参数不容易区别，可传可不传的时候，可以考虑使用Builder建造方法创建。每每当看到别人写的用Bulder方式来调用，就觉得so cool，那就自己也来用Builder方式创建对象吧。

现在要录入一系列人员的基本信息的示例：

创建Person类

public class Person {
    private String name;
    private int age;
    private float height;
    private float weight;

    public Person(String name, int age, float height, float weight) {
        this.name = name;
        this.age = age;
        this.height = height;
        this.weight = weight;
    }

    public String getName() {
        return name;
    }

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

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public float getHeight() {
        return height;
    }

    public void setHeight(float height) {
        this.height = height;
    }

    public float getWeight() {
        return weight;
    }

    public void setWeight(float weight) {
        this.weight = weight;
    }
}

那么创建对象就是这样，后面参数不容易看出表示的是什么，可读性不强

        new Person("冯提莫",18,150,43);
        new Person("温婉",17,164,48);

用Builder模式进行改造

创建一个Builder类，属性和Person类一样，加上SetXxx()方法

static class Builder{
        private String name;
        private int age;
        private float height;
        private float weight;

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

        public void setAge(int age) {
            this.age = age;
        }

        public void setHeight(float height) {
            this.height = height;
        }

        public void setWeight(float weight) {
            this.weight = weight;
        }
}

将Person的构造方法改为传入Builder对象，将Builder对象的属性值都赋予Person对象

    public Person(Builder builder){
        this.name = builder.name;
        this.age = builder.age;
        this.height = builder.height;
        this.weight = builder.weight;
    }

改造Builder类，关键步骤是将各个set方法返回Builder类对象，这样就能继续愉快地连续调用set方法了，最后调用build()创建方法返回Person对象。

static class Builder{
        private String name;
        private int age;
        private float height;
        private float weight;

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

        public Builder setAge(int age) {
            this.age = age;
            return this;
        }

        public Builder setHeight(float height) {
            this.height = height;
            return this;
        }

        public Builder setWeight(float weight) {
            this.weight = weight;
            return this;
        }

        public Person build(){
            return new Person(this);
        }
    }

将各个set方法的返回值类型改为Builder，每次都返回builder对象，这样才能将set方法实现连续的链式调用。
build()方法创建一个person对象，会调用Person的带参构造方法，将builder对象的属性依次赋予person对象。person中的属性值就是链式调用set方法的各个值。

使用Builder模式创建Person对象，明显看出代码可读性大大增强。注：Builder创建方式通常是在创建的对象少的情况下使用。

Person person = new Person.Builder()
            .setName("莉哥")
            .setAge(20)
            .setHeight(162)
            .setWeight(45)
            .build();