difference between accessing the variable directly and using properties

[NareshN]

Hi All,

can u tell me difference between accessing the EmpId directly and using properties.How we can prevent data loss.This concept is called Encapsulation.
what happens if i use varibles direrctly.please explain me clearly

int m_employeeId;
string m_employeeName;
public int EmployeeId
{
get { return m_employeeId;
}
set
{
m_employeeId = value;
}

}
public string EmployeeName
{
get { return m_employeeName;
}
set
{
m_employeeName = value;
}
}

[Junky]

There are so many things wrong with that code that I'm not going to bother.

[goldest]

OP,

Go through these links: Encapsulation

What are Accessors and Mutators and how to use them: Java Accessors Mutators

You could have easily Googled them, but anyways...

Hope that helps,

Goldest

[goldest]

And yes, use Code Tags next time onwards while posting your code.

Goldest

[NareshN]

Hi,

In encapsulation concept can anyone explain this line with example.If we change the datatype of field but no need of changin user class.

•The users of a class do not know how the class stores its data. A class can change the data type of a field, and users of the class do not need to change any of their code.

[sunde887]

If all your classes fields are declared public it could cause problems for people using your code. For example, if you change from public to private, they may have code which sets variables manually, this would no longer be allowed. You encapsulate your class so they never have access to the information in the first place, this way, if you make a change, there code isn't affected.

[NareshN]

Hi,

Sorry i didn't get you .

Both is same thing how we are hidindg data.can u please elaborate it.How we preventing accedental loss of data.

This is the interview question i am facing.

[sunde887]

I had a detailed explanation but I realized what you meant with the line you were asking about. If you create a class with private fields, you also have constructors to initialize the members, and methods that allow you to change the fields.

class person{
  private String name;
  private int pn;
  person(){
    name = "bob";
    pn = 10;
  }
  person(String name){
    this.name = name;
    pn = 10;
  }
  person(String name, int pn){
    this.name = name;
    this.pn = pn;
  }
  public String lookupname(){
    return name;
  }
  public int lookupnum(){
    return pn;
  }
}

public class loblah{
  public static void main(String[] args){
    person chris = new person("Chris", 100);
    person john = new person("John");
    person liz = new person();
    chris.lookupname();
    chris.lookupnum();
    john.lookupname();
    john.lookupnum();
    liz.lookupname();
    liz.lookupnum();
  }
}

in this example, for some reason you do not want people to access the data fields directly, but they need to be able to create a person object somehow. If you declare it public something you may not want happening may happen, so you declare it private and create methods to lookup the information, and constructors to initialize the person.

if all the fields are public something may happen which doesn't cause an error but can give you results that are different with what you expect.

same code without encapsulation:

class Person{
	public String name;
	public int pn;
}

public class Loblah{
	public static void main(String[] args){
		Person chris = new Person();
		chris.name = "Chris";
		chris.pn = 10;
		Person john = new Person();
		john.name = "John";
		john.pn = 20;
		Person liz = new Person();
		liz.name = "Liz";
		liz.pn = 30;
		System.out.println(liz.name + " " + liz.pn);
		System.out.println(john.name + " " + john.pn);
		System.out.println(chris.name + " " + chris.pn);
	}
}

You may have circumstances where you don't want the classes information to be able to be changed by another class.

read that and see if it helps you at all:
Java Tutorial 4 - Encapsulation and Classes

[Tolls]

As another example, slightly more complex perhaps.

public class MyDateClass {
    public Date date;
}

With an object of this class I can change the values in date by using date.setTime(). MyDateClass may need to do some work when a date is changed (recalculate interest, say), but now it can't do that work since it has no idea that date has changed.

public class MyBetterDateClass {
    private Date date;

    public Date getDate() {
        return date.clone();
    }
    public void setDate(Date date) {
        this.date = date;
        recalculateStuff();
    }
}

Now I'm only supplying a copy of my date class which means that no one can change my data (without cheating anyway) without me knowing, so I can now do my recalculations whenever the date changes.