non-static variable cant be referenced from a static context

[Ben Hultin]

As I have been working on this program, I keep running into static issues. My latest static error is:

BenHultinProg2.java:29: non-static variable hw4 cannot be referenced from a stat
ic context
double totalPPoints = hw1.getPPoints() + hw2.getPPoints() + hw3.
getPPoints() + hw4.getPPoints();

^
BenHultinProg2.java:34: non-static variable lGrade cannot be referenced from a s
tatic context
lGrade = totalEPoints / totalPPoints;
^
BenHultinProg2.java:36: non-static variable lGrade cannot be referenced from a s
tatic context
if (lGrade >= 0.9) {
^

Trying to avoid static errors I have put a methods content into a the main method, which just created more static errors.

This is currently what I have now.

  




public class BenHultinProg2
{

	double lGrade;
	
	HwScore hw1 = new HwScore(26.5, 30.0); // 26 earned points, 30 possible points
			
	HwScore hw2 = new HwScore(29.0, 27.5); // 29 earned points, 27 possible points
			
	HwScore hw3 = new HwScore(0.0, 20.0); // 0 earned points, 20 possible points
			
	HwScore hw4 = new HwScore(16.0, 20.0); // 16 earned points, 20 possible points

	
    public static void main (String[] args)
    {
	
	new BenHultinProg2();
	
	//printOverallGrade();
	
		double totalEPoints = hw1.getEPoints() + hw2.getEPoints() + hw3.getEPoints() + hw4.getEPoints();

		double totalPPoints = hw1.getPPoints() + hw2.getPPoints() + hw3.getPPoints() + hw4.getPPoints();
		
		System.out.println(totalEPoints); // earned points
		System.out.println(totalPPoints); // possible points
		
		lGrade = totalEPoints / totalPPoints;
		
		if (lGrade >= 0.9) {
			System.out.println("A");
			
		} else if (lGrade >= 0.8) {	
			System.out.println("B");
			
		} else if (lGrade >= 0.7) {	
			System.out.println("C");	
			
		} else {	
			System.out.println("D");	
		}	
	
	} // end main method
	
	
	public BenHultinProg2 () {
	
		
	
		hw1.printGrade();
		hw2.printGrade();
		hw3.printGrade();
	
	}
	
	
	// public void  printOverallGrade () {
	
	
	
	
	// } // end printOverallGrade method
} // end main class

  

and my driven class is:

   



public class HwScore {

	double ePoints;
	double pPoints;
	double lGrade;
	
	


	public HwScore (double e, double p) {
	
	this.ePoints = e;
	this.pPoints = p;
	
	}
	
	
	
	private void letterGrade () {
	
		if (lGrade >= 0.9) {
			System.out.println("A");
			
		} else if (lGrade >= 0.8) {	
			System.out.println("B");
			
		} else if (lGrade >= 0.7) {	
			System.out.println("C");	
			
		} else {	
			System.out.println("D");	
		}	
		
		
	}
	
	
	


	public void printGrade () {
	

	
	System.out.println(ePoints); // earned points
	System.out.println(pPoints); // possible points
	
	lGrade = ePoints / pPoints;
	letterGrade();
	
	
	}
	
	public void setEPoints(double newEPoints)
    {
        ePoints = newEPoints; 
    }
	
	public void setPPoints(double newPPoints)
    {
        pPoints = newPPoints; 
    }
	
	public double getEPoints()
    {
        return ePoints; 
    }
	
	public double getPPoints()
    {
        return pPoints; 
    }


}

 

I appreciate any help in the matter

[fred rosenberger]

Static methods/variable exist regardless of whether or not you create the object where they are defined.

Non-static methods/variables don't exist until you create an object.

So, if you try and use a non-static thing from a static context, the java compiler tells you 'Hey - that thing doesn't exist yet'.

on line 23 in your main, you create a new BenHultinProg2 object, but you don't SAVE it anywhere. So you have created all those HwScore objects, but they all get lost since there is no active reference anymore. you need to do something like this:

BenHultinProg2 myProg2 = new BenHultinProg2();

then you'll need to do this:

double totalEPoints = myProg2.hw1.getEPoints() + myProg2.hw2.getEPoints() + myProg2.hw3.getEPoints() + myProg2.hw4.getEPoints();

[Ben Hultin]

thanks a lot for the help, I will definelty save that explanation of static and non-static variables. With that I was able to fix everything. My program now works and Im done with the assignment! Thanks again for the help.