62 lines
2.0 KiB
Markdown
62 lines
2.0 KiB
Markdown
---
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title: POJO
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---
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## POJO
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POJO stands for "Plain Old Java Object". This is different from Plain Old _Javascript_ Objects.
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A Plain Old Java Object refers to the Object Oriented Programming (OOP) paradigm that is used in the Java programming language. The [OOP model](https://en.wikipedia.org/wiki/Object-oriented_programming) treats data as 'objects'. Each 'object' is an instance of a 'Class', which represents the archetype or template from which all objects inherit their properties and attributes.
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A POJO is therefore simply a Java Object. However, it must also satisfy the following additional criteria:
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1. it must not extend prespecified Java Classes;
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```java
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public class Foo extends javax.servlet.http.HttpServlet {
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...// body ...
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}
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```
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2. it must not implement prespecified Interfaces;
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```java
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public class Bar implements javax.ejb.EntityBean {
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... // body
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}
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```
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3. it must not contain prespecified Annotations.
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```java
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@javax.persistence.Entity public class Baz {
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... // body ...
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}
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```
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4. For any class field which is marked as private it must have getter and setter methods alongside it. Also it must have EMPTY constructor if custom constructor declared.
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```
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public class Car {
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private int gear;
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// default constructor
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public Car() { }
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// custom constructor
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public Car(int car){
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this.car = car;
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}
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public int getGear() {
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return this.gear;
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}
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public void setGear(int gear){
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this.gear = gear;
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}
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}
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```
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Therefore a Java Object qualifies as a POJO only when it is free from the above modifications. It therefore follows that a POJO is not 'bound by any restrictions' other those prescribed by the formal Java language specification.
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POJO is usually used to describe a class that doesn't need to be a subclass of anything, or implement specific interfaces, or follow a specific pattern. It has properties, getters and setters for respective properties. It may also override Object.toString() and Object.equals().
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#### More Information:
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[Wikipedia - POJOs](https://en.wikipedia.org/wiki/Plain_old_Java_object)
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