java 构建者模式

In my last post, I explained about Builder Pattern in Java. Sometime back I wrote an article about how to create immutable class in java. In this post, we will learn how easy it’s to create java immutable class using Builder pattern. Using builder pattern to create immutable class is a good approach when the number of arguments in the Constructor is more that can cause confusion in their ordering.

在上一篇文章中，我解释了Java中的Builder模式 。 有时我写了一篇关于如何在java中创建不可变类的文章。 在这篇文章中，我们将学习使用Builder模式创建Java不可变类是多么容易。 当构造函数中的参数数量更多而可能导致其顺序混乱时，使用构造器模式创建不可变类是一种好方法。

Java不可变类要点 (Java Immutable class important points)

• The immutable class should have only getter methods.不可变类应仅具有getter方法。
• The immutable class will have a private constructor with Builder object as parameter that will be used to create the immutable class.不可变类将具有一个私有构造函数，其中带有Builder对象作为参数，将用于创建不可变类。
• If the immutable class attributes are not immutable, for example HashMap, we should perform deep copy or cloning to avoid modification of its attributes.如果不可更改的类属性不是不可更改的，例如HashMap，则应执行深度复制或克隆操作，以避免对其属性进行修改。
• Using Builder pattern is easy when number of optional attributes are more in the immutable class.当不可变类中的可选属性数量更多时，使用Builder模式很容易。

Java不可变类–构建器模式 (Java Immutable Class – Builder Pattern)

Here is the implementation of an immutable class in java using Builder pattern.

这是使用Builder模式在Java中实现不可变类的实现。

package com.journaldev.design.builder;import java.util.HashMap;public class ImmutableClass {//required fieldsprivate int id;private String name;//optional fieldsprivate HashMap<String, String> properties;private String company;public int getId() {return id;}public String getName() {return name;}public HashMap<String, String> getProperties() {//return cloned object to avoid changing it by the client applicationreturn (HashMap<String, String>) properties.clone();}public String getCompany() {return company;}private ImmutableClass(ImmutableClassBuilder builder) {this.id = builder.id;this.name = builder.name;this.properties = builder.properties;this.company = builder.company;}//Builder classpublic static class ImmutableClassBuilder{//required fieldsprivate int id;private String name;//optional fieldsprivate HashMap<String, String> properties;private String company;public ImmutableClassBuilder(int i, String nm){this.id=i;this.name=nm;}public ImmutableClassBuilder setProperties(HashMap<String,String> hm){this.properties = (HashMap<String, String>) hm.clone();return this;}public ImmutableClassBuilder setCompany(String comp){this.company = comp;return this;}public ImmutableClass build(){return new ImmutableClass(this);}}
}

Here is the test program to check if the object we create is immutable or not.

这是测试程序，用于检查我们创建的对象是否不可变。

package com.journaldev.design.test;import java.util.HashMap;import com.journaldev.design.builder.ImmutableClass;public class ImmutableBuilderTest {public static void main(String[] args) {// Getting immutable class only with required parametersImmutableClass immutableClass = new ImmutableClass.ImmutableClassBuilder(1, "Pankaj").build();HashMap<String,String> hm = new HashMap<String, String>();hm.put("Name", "Pankaj");hm.put("City", "San Jose");// Getting immutable class with optional parametersImmutableClass immutableClass1 = new ImmutableClass.ImmutableClassBuilder(1, "Pankaj").setCompany("Apple").setProperties(hm).build();//Testing immutabilityHashMap<String,String> hm1 = immutableClass1.getProperties();//lets modify the Object passed as argument or get from the Objecthm1.put("test", "test");hm.put("test", "test");//check that immutable class properties are not changedSystem.out.println(immutableClass1.getProperties());}}

That’s all for creating immutable class in java using builder pattern.

这就是使用生成器模式在Java中创建不可变类的全部内容。

Reference: Oracle Documentation

参考： Oracle文档

翻译自: https://www.journaldev.com/1432/java-immutable-class-builder

java 构建者模式