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

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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

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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：

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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 + ")"; } } }