CODEWITHSUNDEEP
javaoopsettergetter
EMMERZOH
EMMERZOH

Reputation: 29

Updating instance variable values and ensuring private methods use them - Java

I have constructed a class that will compute an equation based on private instance variables.

These variables may be updated using getter and setter methods, the latter of which are called and changed from a separate control class within the project (I am using Eclipse if that is relavant)

I need to ensure that the constructor uses the updated values when passed from the separate control class to the setter methods in computing variable c.

Here is snipets of my code.

instance variables

    private double a;
    private double b; 
    private double c;

constructor

public Prob(){
    a = 4; //must be first initialized with these values then later changed from the control class
    b = 10;
    setA(a);
    setB(b);
    setC();

setter methods

public void setA(double a){
    if(isValidA(a))
        this.a = a;
    else this.a = 100; // 100 is meaningless and allows execution of "invalid" string
            }
public void setB(double b){
    if(isValidB(b))
        this.b = b;
    else this.b = -1; // -1 is meaningless, allows execution "invalid entry" code in string
        }

private void setC(){
        if(a<=5 && b>=2)
             c = (int)(5 + 0.5*a - 5*(Math.pow(b, 0.2)) + 0.5*(a)*b;
       else c = a; 
}

I can update variable a or variable b from the control class but how can I get variable c to update as well based on the current a and b?

Upvotes: 0

Views: 5169

Answers (2)

Eran
Eran

Reputation: 393956

If c depends on a and b, you should either call setC from setA and setB, or call setC after each time you call setA or setB.

The former would be cleaner to implement, but may cause redundant calculations (if you update both a and b at the same time, it would call setC twice).

The latter would be more efficient (since if you call both setA and setB, you can explicitelly call setC once after these two calls), but more bug prone (since you might forget to call setC in some of the places you call setA or setB).

Another option, which I think is the best, is to calculate c on demand in getC, and cache the result (so that following calls to getC won't have to recalculate its value, unless a or b are changed). In this case you don't need setC. You'll need to add a boolean member cIsValid that would be an indicator of whether the cached value of c is valid.

public double getC () 
{
  if (!cIsValid) {
       if(a<=5 && b>=2)
            c = (int)(5 + 0.5*a - 5*(Math.pow(b, 0.2)) + 0.5*(a)*b;
       else 
            c = a;
  }
  cIsValid = true;
  return c;
}

And in setA and setB you invalidate the cache by setting cIsValid to false :

public void setA(double a)
{
    if(isValidA(a))
        this.a = a;
    else 
        this.a = 100; // 100 is meaningless and allows execution of "invalid" string
    cIsValid = false;
}

public void setB(double b)
{
    if(isValidB(b))
        this.b = b;
    else 
        this.a = -1; // -1 is meaningless, allows execution "invalid entry" code in string
    cIsValid = false;
}

Upvotes: 0

Elliott Frisch
Elliott Frisch

Reputation: 201497

If I understand your question, then you could setA and setB like so

public void setA(double a) {
  this.a = (isValidA(a)) ? a : 100;
  setC(); // <-- call setC();
}
public void setB(double b) {
  this.b = (isValidB(b)) ? b : -1;
  setC(); // <-- call setC();
}

Upvotes: 2

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