Java - Encapsulation

JAVA - ENCAPSULATION



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Encapsulat ion is one of t he four fundament al OOP concept s. The ot her t hree are inherit ance, polymorphism, and abst ract ion.

Encapsulat ion is t he t echnique of making t he fields in a class privat e and providing access t o t he fields via public met hods. If a field is declared privat e, it cannot be accessed by anyone out side t he class, t hereby hiding t he fields wit hin t he class. For t his reason, encapsulat ion is also referred t o as dat a hiding.

Encapsulat ion can be described as a prot ect ive barrier t hat prevent s t he code and dat a being randomly accessed by ot her code defined out side t he class. Access t o t he dat a and code is t ight ly cont rolled by an int erface.

The main benefit of encapsulat ion is t he abilit y t o modify our implement ed code wit hout breaking t he code of ot hers who use our code. Wit h t his feat ure Encapsulat ion gives maint ainabilit y, flexibilit y and ext ensibilit y t o our code.

Example:

Let us look at an example t hat depict s encapsulat ion:

/* File name : EncapTest.java */ public class EncapTest{

private String name; private String idNum; private int age;

public int getAge(){ return age;

}

public String getName(){ return name;

}

public String getIdNum(){ return idNum;

}

public void setAge( int newAge){ age = newAge;

}

public void setName(String newName){ name = newName;

}

public void setIdNum( String newId){ idNum = newId;

} }

The public met hods are t he access point s t o t his class' fields from t he out side java world. Normally, t hese met hods are referred as get t ers and set t ers. Therefore any class t hat want s t o access t he variables should access t hem t hrough t hese get t ers and set t ers.

The variables of t he EncapTest class can be access as below::

/* File name : RunEncap.java */ public class RunEncap{

public static void main(String args[]){ EncapTest encap = new EncapTest(); encap.setName("James");

encap.setAge(20); encap.setIdNum("12343ms");

System.out.print("Name : " + encap.getName()+ " Age : "+ encap.getAge());

} }

This would produce t he following result :

Name : James Age : 20

Benefit s of Encapsulat ion:

The fields of a class can be made read-only or writ e-only.

A class can have t ot al cont rol over what is st ored in it s fields.

The users of a class do not know how t he class st ores it s dat a. A class can change t he dat a t ype of a field and users of t he class do not need t o change any of t heir code.

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