Current Object confusion

[Roscoe Jb]

Hello all, first time poster and slowly but surely learning java. i have a question for a program im trying to create. im told that one of the methods should be:

this method takes one parameter (a Polynomial). It will return a new Polynomial that is equal to the sum of the current object and the parameter. (Do not modify the current object.)

here is what i have

  	public Polynomial add(Polynomial poly) {
		return new Polynomial(); 
	}   

and....im stuck. i dont understand, the current object? what would be considered the current object? Thank you all

[pete stein]

The current object is the one that's calling the method including all of its fields and such. So assuming your class has an int field called intField, you could add two like so:

private int intField;

public int add(MyClass otherObject) {
  int sum = intField /* the current object's intField */ + 
          otherObject.intField;  

  return sum
}

[Janeice DelVecchio]

And Welcome to JavaRanch!

[Roscoe Jb]

pete stein wrote:The current object is the one that's calling the method including all of its fields and such. So assuming your class has an int field called intField, you could add two like so:

private int intField;

public int add(MyClass otherObject) {
  int sum = intField /* the current object's intField */ + 
          otherObject.intField;  

  return sum
}

and if i had 3 current objects? (if im reading what you told me correctly)

  	private final MyDouble a;
	private final MyDouble b;
	private final MyDouble c;  

Janeice DelVecchio wrote:And Welcome to JavaRanch!

thank you ive heard good things about this ranch, glad i came here

[Jim Hoglund]

It may be helpful to take what Pete said above and add a bit more context.

class MyClass {
   public int intField = 23;
   public int add(MyClass otherObject) {
      int sum = intField + otherObject.intField;  
      return sum;
   } 
}

      MyClass co = new MyClass();
      MyClass pin = new MyClass();
      int result = co.add(pin);  

Your program would then create two instances of MyClass, one for your current
object, call it 'co', and the second called 'pin' that you want to add to 'co' (pass
in to co's add() method). This would look like lines 09-11 above, but you have
to put the main program around it, of course.

Jim ... ...

[pete stein]

Roscoe [surl='http://jenkins-ci.org/' class='api' title='Continuous Integration Engine wrote:Jenkins[/surl]]
and if i had 3 current objects? (if im reading what you told me correctly)

  	private final MyDouble a;
	private final MyDouble b;
	private final MyDouble c;  

Sorry no, I must not have communicated this well. You can only have one current object at any one time, but here that object has 3 fields.

[Md Ibrahim]

hi Roscoe,

First of all understand that Object is a behavioral representation of a Class at runtime,

Eg:

Assume You have written a Class name Vehicle.Java and an attribute say Speed

public Class Vehicle {

private int Speed;

public getSpeed() {

this.speed
}

public setSpeed(Speed pSpeed){
this.speed =pSpeed
}

}
This is the physical Calss which you have written and eligible to compile.

But Creating Objects out of it happens at runtime,

Vehicle aCar = new Vehicle();
aCar.setSpeed(100)

Vehicle aByke = new Vehcle();
aByke.setSpeed(50);

Now aCar and aByke will have their own speed attribute values at runtime since they are
Objects at runtime. They only stay till the Objects Live.

So now ask yourself this question of How it makes sense by telling we can add two objects
like below.
In the below code this keyword refers to current object and pVehicle the passed in Parameter Object of same type.

# public Vehicle add(Vehicle pVehicle) {
# return new (this + pVehicle) ; // And what in the world this means to be?? :-)
# }


we cant say aCar + aByke.(adding two objects)


But Yes we can add Primitive dataType objects as given an example by pete stein

Do write back if you are still in cofusion to differentiate between object and a Class

By,
Ibrahim

[Roscoe Jb]

Wow all these replies! Thank you all!! this is what i am left with right now:

  	public Polynomial add(Polynomial poly) {
		MyDouble sum = a.add(poly.a);
		MyDouble sum2 = b.add(poly.b);
		MyDouble sum3 = c.add(poly.c);
		MyDouble total = sum.add(sum2);
		MyDouble total2 = total.add(sum3);
		return new Polynomial(total2); 
	}   

i believe this is what the requirement for the method is referring to, add the a, b, c of the current object with the a, b, c of the polynomial passed through. i believe this is correct?

I am also supposed to input a junit test with this, though i am completely confused how to do it with this method. ive done it with others, just not this one. im not exactly sure how to even test a method like this, assuming its done correctly. any ideas please? Thanks again

[pete stein]

Can you show us what your Polynomial class constructors look like?

edit: and what is MyDouble?

[Roscoe Jb]

This is the polynomial class (though much work needed)

 
public class Polynomial {
	private final MyDouble a;
	private final MyDouble b;
	private final MyDouble c;
	
	public Polynomial (MyDouble a, MyDouble b, MyDouble c){
		this.a = a;
		this.b = b;
		this.c = c;
	}
	
	public Polynomial (MyDouble b, MyDouble c){
		a = new MyDouble(0);
		this.b = b;
		this.c = c;
	}
	
	public Polynomial (MyDouble c){
		a = new MyDouble (0);
		b = new MyDouble (0);
		this.c = c;
	}
	
	public Polynomial (){
		a = new MyDouble (0);
		b = new MyDouble (0);
		c = new MyDouble (0);
	}
	
	public Polynomial (Polynomial poly){
		this.a = poly.a;
		this.b = poly.b;
		this.c = poly.c;
	}
	
	
	
	public MyDouble getA(){
		return a;
	}
	
	public MyDouble getB(){
		return b;
	}
	
	public MyDouble getC(){
		return c;
	}
	
	public MyDouble eval(MyDouble x){
		MyDouble a = getA();
		MyDouble b = getB();
		MyDouble c = getC();
		MyDouble squareX = (x.square());//square x^2
		MyDouble multiplyA = squareX.multiply(a);//add square to a
		MyDouble multiplyB = b.multiply(x);//compute b
		MyDouble addC = c.add(multiplyB);//add c and b
		MyDouble addABC = multiplyA.add(addC);//add a and (c and b (addC))
		x = addABC;//x equals adding of a b and c
		return x;
	}
	
	public Polynomial add(Polynomial poly) {
		MyDouble sum = a.add(poly.a);
		MyDouble sum2 = b.add(poly.b);
		MyDouble sum3 = c.add(poly.c);
		MyDouble total = sum.add(sum2);
		MyDouble total2 = total.add(sum3);
		return new Polynomial(total2); 
	} 
	
	public Polynomial subtract(Polynomial poly) {
		MyDouble sum = a.subtract(poly.a);
		MyDouble sum2 = b.subtract(poly.b);
		MyDouble sum3 = c.subtract(poly.c);
		MyDouble total = sum.subtract(sum2);
		MyDouble total2 = total.subtract(sum3);
		return new Polynomial(total2); 
	} 
	
	public Polynomial limitedMultiply(Polynomial poly) {
		return new Polynomial();
	} 
	
	public Polynomial derivative() {
		//Polynomial poly = new Polynomial (a, b, c);
		MyDouble x = new MyDouble(3);
		MyDouble a = getA();
		MyDouble b = getB();
		MyDouble two = new MyDouble(2);
		MyDouble multiply2 = a.multiply(two);
		MyDouble multiplyX = multiply2.multiply(x);
		MyDouble addB = multiplyX.add(b);
		return new Polynomial();
	} 
	
	public boolean equals() {
		if()
		return true;
	} 
	
	public Polynomial norm() {
		return new Polynomial();
	}
	
	public int compareTo(Polynomial poly){
		int value = 0;
		return value;
	}
	
	public String toString(){
		String z = "";
		return z;
	}
	
	public static Polynomial parsePolynomial(String z){
		return new Polynomial();
	}
}  

And this is mydouble:

 
public class MyDouble {	
	private double doubleValue;
	private final static double EPSILON = 0.0001;
	

	protected static boolean toStringUsed = false;


	public static MyDouble zero = new MyDouble(0);
	
	
	public static MyDouble parseDouble(String str) {
		return new MyDouble(Double.parseDouble(str));
	}
	
	
	public MyDouble(double passedDouble) {
		this.doubleValue = passedDouble;
	}
	
	
	public MyDouble(MyDouble passedMyDouble) {
		doubleValue = passedMyDouble.doubleValue;
	}
	

	public MyDouble add(MyDouble passedVal) {
		return new MyDouble(this.doubleValue + passedVal.doubleValue);
	}
	

	public MyDouble subtract(MyDouble passedVal) {
		return new MyDouble(this.doubleValue - passedVal.doubleValue);
	}
	

	public MyDouble multiply(MyDouble passedVal) {
		return new MyDouble(this.doubleValue * passedVal.doubleValue);
		
	}

	public MyDouble divide(MyDouble passedVal) {
		return new MyDouble(this.doubleValue / passedVal.doubleValue);
	}

	public MyDouble sqrt() {
		return new MyDouble(Math.sqrt(this.doubleValue));
	}
	
	public MyDouble square() {
		return new MyDouble(this.doubleValue * this.doubleValue);
	}


	public int compareTo(MyDouble passedVal) {
		if (Math.abs(this.doubleValue - passedVal.doubleValue) < EPSILON)
			return 0;
		else if (this.doubleValue < passedVal.doubleValue)
			return -1;
		else
			return 1;
	}
	

	public boolean equals(MyDouble passedVal) {
		if (passedVal == null) {
			return false;
		}
		return Math.abs(this.doubleValue - passedVal.doubleValue) < EPSILON;
	}

	public boolean isZero() {
		return (Math.abs(this.doubleValue) < EPSILON);
	}
	
	public MyDouble abs() {
		return new MyDouble(Math.abs(this.doubleValue));
	}

	public String toString() {
		toStringUsed = true;
		if (((int)this.doubleValue) == this.doubleValue) {
			return new Integer((int)this.doubleValue).toString();
		} else {
			return new Double(this.doubleValue).toString();
		}
	}
}   

[pete stein]

Roscoe Jb wrote:This is the polynomial class (though much work needed)

 
public class Polynomial {
	private final MyDouble a;
	private final MyDouble b;
	private final MyDouble c;
	
	public Polynomial (MyDouble a, MyDouble b, MyDouble c){
		this.a = a;
		this.b = b;
		this.c = c;
	}
	

As I thought. Wouldn't you rather use this constructor above that takes three MyDouble objects as parameters rather than your current attempt where you combine the new a, b, and c all into one MyDouble object? Which makes more sense?