考虑使用构建器（二）

考虑使用构建器

这个比较好理解，能够解决多参数构造器的复杂性，相对于get和set的JavaBean来说也有线程安全性的优势，个人倾向于使用lombok的@Builder注解，注解虽好用，不过也需要了解下注解背后的一些原理。

先看一下我写的一个简单示例


public class  {

	private String name;
	
	private int age;
	
	public static void main(String[] args) {
    
    	Person p = Person.builder().age(15).build();
   
	} 
}

再看下官方的标准示例


import lombok.Builder;
import java.util.Set;


public class BuilderExample {
   private String name;
   private int age;
   @Singular
   private Set<String> occupations;
}

等效代码：

import java.util.Set;
class BuilderExample {
    private String name;
    private int age;
    private Set<String> occupations;

    BuilderExample(String name, int age, Set<String> occupations) {
        this.na 大专栏  考虑使用构建器（二）me = name;
        this.age = age;
        this.occupations = occupations;
    }

    public static BuilderExampleBuilder builder() {
        return new BuilderExampleBuilder();
    }

    public static class BuilderExampleBuilder {
        private String name;
        private int age;
        private java.util.ArrayList<String> occupations;

        BuilderExampleBuilder() {
        }

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

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

        public BuilderExampleBuilder occupation(String occupation) {
            if (this.occupations == null) {
                this.occupations = new java.util.ArrayList<String>();
            }

            this.occupations.add(occupation);
            return this;
        }

        public BuilderExampleBuilder occupations(Collection<? extends String> occupations) {
            if (this.occupations == null) {
                this.occupations = new java.util.ArrayList<String>();
            }

            this.occupations.addAll(occupations);
            return this;
        }

        public BuilderExampleBuilder clearOccupations() {
            if (this.occupations != null) {
                this.occupations.clear();
            }

            return this;
        }

        public BuilderExample build() {
            // complicated switch statement to produce a compact properly sized immutable set omitted.
            // go to https://projectlombok.org/features/Singular-snippet.html to see it.
            Set<String> occupations = ...;
            return new BuilderExample(name, age, occupations);
        }

        @java.lang.Override
        public String toString() {
            return "BuilderExample.BuilderExampleBuilder(name = " + this.name + ", age = " + this.age + ", occupations = " + this.occupations + ")";
        }
    }
}