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iluwatar#1638 Add Parameter Object pattern (iluwatar#1650)
* iluwatar#1638 Add Parameter Object pattern * iluwatar#1638 Fix comments and formatting for Parameter Object pattern * iluwatar#1638 Fix formatting, commenting, remove string concatenation in Parameter Object pattern * iluwatar#1638 Fix readme formatting and log parameter object
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‎parameter-object/README.md

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---
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layout: pattern
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title: Parameter Object
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folder: parameter-object
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permalink: /patterns/parameter-object/
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categories: Behavioral
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tags:
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- Extensibility
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---
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## Intent
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The syntax of Java language doesn’t allow you to declare a method with a predefined value
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for a parameter. Probably the best option to achieve default method parameters in Java is
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by using the method overloading. Method overloading allows you to declare several methods
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with the same name but with a different number of parameters. But the main problem with
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method overloading as a solution for default parameter values reveals itself when a method
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accepts multiple parameters. Creating an overloaded method for each possible combination of
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parameters might be cumbersome. To deal with this issue, the Parameter Object pattern is used.
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## Explanation
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The Parameter Object is simply a wrapper object for all parameters of a method.
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It is nothing more than just a regular POJO. The advantage of the Parameter Object over a
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regular method parameter list is the fact that class fields can have default values.
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Once the wrapper class is created for the method parameter list, a corresponding builder class
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is also created. Usually it's an inner static class. The final step is to use the builder
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to construct a new parameter object. For those parameters that are skipped,
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their default values are going to be used.
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**Programmatic Example**
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Here's the simple `SearchService` class where Method Overloading is used to default values here. To use method overloading, either the number of arguments or argument type has to be different.
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```java
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public class SearchService {
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//Method Overloading example. SortOrder is defaulted in this method
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public String search(String type, String sortBy) {
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return getQuerySummary(type, sortBy, SortOrder.DESC);
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}
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/* Method Overloading example. SortBy is defaulted in this method. Note that the type has to be
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different here to overload the method */
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public String search(String type, SortOrder sortOrder) {
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return getQuerySummary(type, "price", sortOrder);
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}
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private String getQuerySummary(String type, String sortBy, SortOrder sortOrder) {
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return "Requesting shoes of type \"" + type + "\" sorted by \"" + sortBy + "\" in \""
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+ sortOrder.getValue() + "ending\" order...";
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}
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}
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```
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Next we present the `SearchService` with `ParameterObject` created with Builder pattern.
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```java
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public class SearchService {
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/* Parameter Object example. Default values are abstracted into the Parameter Object
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at the time of Object creation */
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public String search(ParameterObject parameterObject) {
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return getQuerySummary(parameterObject.getType(), parameterObject.getSortBy(),
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parameterObject.getSortOrder());
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}
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private String getQuerySummary(String type, String sortBy, SortOrder sortOrder) {
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return "Requesting shoes of type \"" + type + "\" sorted by \"" + sortBy + "\" in \""
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+ sortOrder.getValue() + "ending\" order...";
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}
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}
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public class ParameterObject {
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public static final String DEFAULT_SORT_BY = "price";
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public static final SortOrder DEFAULT_SORT_ORDER = SortOrder.ASC;
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private String type;
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private String sortBy = DEFAULT_SORT_BY;
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private SortOrder sortOrder = DEFAULT_SORT_ORDER;
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private ParameterObject(Builder builder) {
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type = builder.type;
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sortBy = builder.sortBy != null && !builder.sortBy.isBlank() ? builder.sortBy : sortBy;
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sortOrder = builder.sortOrder != null ? builder.sortOrder : sortOrder;
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}
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public static Builder newBuilder() {
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return new Builder();
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}
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//Getters and Setters...
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public static final class Builder {
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private String type;
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private String sortBy;
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private SortOrder sortOrder;
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private Builder() {
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}
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public Builder withType(String type) {
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this.type = type;
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return this;
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}
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public Builder sortBy(String sortBy) {
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this.sortBy = sortBy;
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return this;
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}
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public Builder sortOrder(SortOrder sortOrder) {
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this.sortOrder = sortOrder;
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return this;
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}
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public ParameterObject build() {
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return new ParameterObject(this);
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}
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}
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}
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```
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## Class diagram
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![alt text](./etc/parameter-object.png "Parameter Object")
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## Applicability
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This pattern shows us the way to have default parameters for a method in Java as the language doesn't default parameters feature out of the box.
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## Credits
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- [Does Java have default parameters?](http://dolszewski.com/java/java-default-parameters)

‎parameter-object/etc/parameter-object.png

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‎parameter-object/etc/parameter-object.urm.puml

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@startuml
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package com.iluwatar.parameter.object {
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class App {
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- LOGGER : Logger {static}
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+ App()
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+ main(args : String[]) {static}
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}
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class ParameterObject {
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+ DEFAULT_SORT_BY : String {static}
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+ DEFAULT_SORT_ORDER : SortOrder {static}
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- sortBy : String
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- sortOrder : SortOrder
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- type : String
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- ParameterObject(builder : Builder)
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+ getSortBy() : String
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+ getSortOrder() : SortOrder
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+ getType() : String
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+ newBuilder() : Builder {static}
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+ setSortBy(sortBy : String)
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+ setSortOrder(sortOrder : SortOrder)
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+ setType(type : String)
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}
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class Builder {
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- sortBy : String
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- sortOrder : SortOrder
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- type : String
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- Builder()
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+ build() : ParameterObject
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+ sortBy(sortBy : String) : Builder
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+ sortOrder(sortOrder : SortOrder) : Builder
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+ withType(type : String) : Builder
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}
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class SearchService {
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+ SearchService()
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- getQuerySummary(type : String, sortBy : String, sortOrder : SortOrder) : String
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+ search(parameterObject : ParameterObject) : String
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+ search(type : String, sortBy : String) : String
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+ search(type : String, sortOrder : SortOrder) : String
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}
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enum SortOrder {
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+ ASC {static}
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+ DESC {static}
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- value : String
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+ getValue() : String
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+ valueOf(name : String) : SortOrder {static}
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+ values() : SortOrder[] {static}
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}
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}
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Builder --> "-sortOrder" SortOrder
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Builder ..+ ParameterObject
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ParameterObject --> "-DEFAULT_SORT_ORDER" SortOrder
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@enduml

‎parameter-object/pom.xml

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<?xml version="1.0"?>
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<!--
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The MIT License
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Copyright © 2014-2019 Ilkka Seppälä
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Permission is hereby granted, free of charge, to any person obtaining a copy
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of this software and associated documentation files (the "Software"), to deal
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in the Software without restriction, including without limitation the rights
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to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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copies of the Software, and to permit persons to whom the Software is
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furnished to do so, subject to the following conditions:
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The above copyright notice and this permission notice shall be included in
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all copies or substantial portions of the Software.
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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THE SOFTWARE.
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-->
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<project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd" xmlns="http://maven.apache.org/POM/4.0.0"
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xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
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<modelVersion>4.0.0</modelVersion>
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<parent>
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<groupId>com.iluwatar</groupId>
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<artifactId>java-design-patterns</artifactId>
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<version>1.24.0-SNAPSHOT</version>
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</parent>
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<artifactId>parameter-object</artifactId>
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<dependencies>
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<dependency>
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<groupId>org.junit.jupiter</groupId>
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<artifactId>junit-jupiter-engine</artifactId>
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<scope>test</scope>
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</dependency>
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</dependencies>
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<build>
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<plugins>
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<plugin>
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<groupId>org.apache.maven.plugins</groupId>
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<artifactId>maven-assembly-plugin</artifactId>
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<executions>
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<execution>
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<configuration>
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<archive>
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<manifest>
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<mainClass>com.iluwatar.parameter.object.App</mainClass>
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</manifest>
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</archive>
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</configuration>
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</execution>
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</executions>
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</plugin>
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</plugins>
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</build>
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</project>

‎parameter-object/src/main/java/com/iluwatar/parameter/object/App.java

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/*
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* The MIT License
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* Copyright © 2014-2019 Ilkka Seppälä
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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* THE SOFTWARE.
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*/
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package com.iluwatar.parameter.object;
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import org.slf4j.Logger;
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import org.slf4j.LoggerFactory;
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/**
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* The syntax of Java language doesn’t allow you to declare a method with a predefined value
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* for a parameter. Probably the best option to achieve default method parameters in Java is
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* by using the method overloading. Method overloading allows you to declare several methods
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* with the same name but with a different number of parameters. But the main problem with
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* method overloading as a solution for default parameter values reveals itself when a method
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* accepts multiple parameters. Creating an overloaded method for each possible combination of
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* parameters might be cumbersome. To deal with this issue, the Parameter Object pattern is used.
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* The Parameter Object is simply a wrapper object for all parameters of a method.
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* It is nothing more than just a regular POJO. The advantage of the Parameter Object over a
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* regular method parameter list is the fact that class fields can have default values.
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* Once the wrapper class is created for the method parameter list, a corresponding builder class
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* is also created. Usually it's an inner static class. The final step is to use the builder
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* to construct a new parameter object. For those parameters that are skipped,
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* their default values are going to be used.
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*/
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public class App {
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private static final Logger LOGGER = LoggerFactory.getLogger(App.class);
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/**
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* Program entry point.
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*
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* @param args command line args
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*/
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public static void main(String[] args) {
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ParameterObject params = ParameterObject.newBuilder()
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.withType("sneakers")
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.sortBy("brand")
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.build();
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LOGGER.info(params.toString());
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LOGGER.info(new SearchService().search(params));
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}
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}

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