effective java（一）遇到多个构造器参数 时要考虑用构建器

当一个类的变量比较多，构造函数也比较多，用重载构造函数的方法，会导致有客户端代码比较难维护，用这种Builder构造器来实现，扩展性好，便于维护。

/** * Created by wzj on 2016/9/11. */public class BuilderMode{    private int id;    private String name;    private String age;    private String score;    public static class Builder    {        //初始化        private final int id;        private String name = "";        private String age = "";        private String score = "";        //id是不能够改变的        public Builder(final int id)        {            this.id = id;        }        public Builder name(final String name)        {            this.name = name;            return this;        }        public Builder age(final String age)        {            this.age = age;            return this;        }        public Builder score(final String score)        {            this.score = score;            return this;        }        public BuilderMode build()        {            return new BuilderMode(this);        }    }    //构造函数    public BuilderMode(Builder builder)    {        this.id = builder.id;        this.name = builder.name;        this.age = builder.age;        this.score = builder.score;    }    @Override    public String toString()    {        return id + "--" + name + "--" + age + "--" + score;    }    public static void main(String[] args)    {        //构建对象        BuilderMode.Builder builder = new BuilderMode.Builder(1001);        BuilderMode builderMode = builder.name("wzj").age("23").score("100").build();        System.out.println(builderMode.toString());    }}