How do I handle this reference problem in java?

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January 1st, 2013, 11:52 AM

AngleWyrm

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How do I handle this reference problem in java?

Code:

class foo{
    Dog dogReference;

    foo(Dog _dog){
      dogReference = _dog; 
    }

    public bar(){
      dogReference.name = "Fido"; // fail -- doesn't alter the external _dog
    }
}

How do I manipulate dog data from within the foo class?

January 1st, 2013, 05:54 PM

NormR

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Quote:

How do I manipulate dog data from within the foo class?

Use the reference to the Dog class to access data in the Dog class.

Can you post a small, complete program that compiles, executes and shows the problem?

January 2nd, 2013, 01:42 AM

tvc3mye

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Manipulating data of an instance of class variable

Accessing and manipulating data of a class member within a class using direct reference is a bad practice and it completely beats the purpose of encapsulation in object-oriented software design.

Getter/setter methods can be declared for the purpose of data access by a 3rd party class, where all members in the Dog class should be declared private or protected. The data/class members in the Dog class that are supposed to be accessible by other classes should have their respective getter/setter methods declared in the class itself, and all other classes should only allowed to access/change the values of these data/members via these getter/setter methods.

java Code:

Original - java Code

 
public class Foo{
    Dog dogReference;
 
    public Foo(Dog _dog){
      dogReference = _dog; 
    }
 
    public bar(){
      dogReference.setName("Fido"); 
    }
 
    public void makeDogBark(){
        System.out.println(dogReference.getName());
    }
 
    public static void main(String args[]){
        Foo foo = new Foo(new Dog());
        System.out.println("name of the dog before bar()");
        foo.makeDogBark();
        foo.bar();
        System.out.println("name of the dog after bar()");
        foo.makeDogBark();
    }
}
 
public class Dog {
 
    private String name;
 
    /**
     *  Constructor.
     **/
    public Dog(){
        name = "Dido"; //default name.
    }
    
    /**
     *  Setter for name.
     **/
    public void setName(String _name){
        name = _name;
    }
 
    /**
     *  Getter for name.
     **/
    public String getName(){
        return name;
    }
}

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Last edited by tvc3mye : January 2nd, 2013 at 02:01 AM. Reason: missed out some words and added sample codes

How do I handle this reference problem in java?

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