Error: non-static variable height cannot be referenced from a static context at line

fernando · #1 (**permalink**) 08-01-2007, 05:55 PM

Hi, I have 2 classes (really 3 but the third doesn't need to be involved here)
This program calculates the BMI of a person (I'll work on the formulas as soon as I can get this problem fixed)
I want to get the input (text well it will be a number in this case) from the heights Text Field (GUI.java) (comments explaining at the code area) and put it in a formula under the class getHeight() (bodymassindex.java).

Code:

GUI .javapackage bmi;

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.util.*;
import javax.*;
import bmi.GUI.*;

public class GUI extends JFrame implements Observer {
//Create JTextFields
private JTextField heighttf;
private JTextField weighttf;
private JTextField bmitf;
private JTextField wvtf;
private bodymassindex Body;
private static int height;


//Default Constructor
public GUI(bodymassindex bm) {
super();
Body = bm;
Container contents = getContentPane();

//Create JPanels
JPanel panel1 = new JPanel();
panel1.setLayout(new BorderLayout());

JPanel panel2 = new JPanel();
panel2.setLayout(new GridLayout (1, 3, 5, 20));

JPanel panel3 = new JPanel();
panel3.setLayout(new GridLayout (1, 3, 5, 20));

JPanel panel4 = new JPanel();
panel4.setLayout(new GridLayout (1, 2, 5, 20));

//Create JTextFields
JTextField heighttf = new JTextField();
JTextField weighttf = new JTextField();
JTextField bmitf = new JTextField();
JTextField wvtf = new JTextField();


//Set Editable to False on bmitf and wvtf
heighttf.setEditable(true);
weighttf.setEditable(true);
bmitf.setEditable(false);
wvtf.setEditable(false);

//Create JLabels
JLabel heightl = new JLabel("Height");
JLabel weightl = new JLabel("Weight");
JLabel bmil = new JLabel("BMI");

//Create JButtons
JButton calcb = new JButton("Calculate");

//Add Panels to Panel1
panel1.add(panel2,BorderLayout.NORTH);
panel1.add(panel3,BorderLayout.CENTER);
panel1.add(panel4,BorderLayout.SOUTH);

//Add buttons, text fields, etc to panel2
panel2.add(heightl);
panel2.add(weightl);
panel2.add(bmil);

//Add buttons, text fields, etc to panel3
panel3.add(heighttf);
panel3.add(weighttf);
panel3.add(bmitf);

//Add buttons, text fields, etc to panel4
panel4.add(wvtf);
panel4.add(calcb);

//Set Text Align to Center
weighttf.setHorizontalAlignment(JTextField.CENTER);
heighttf.setHorizontalAlignment(JTextField.CENTER);
bmitf.setHorizontalAlignment(JTextField.CENTER);
wvtf.setHorizontalAlignment(JTextField.CENTER);

//Resgister Listener
weighttf.addActionListener(new weighttfhandler());
heighttf.addActionListener(new heighttfhandler());
calcb.addActionListener(new calcbuttonhandler());

//Frame information
contents.add(panel1);
setTitle("BMI Calculator");
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setSize(200, 100);
setVisible(false);
bmitf.setText("" +Body.getbmi());
}



public void update (Observable o, Object arg) {


}

private class calcbuttonhandler implements ActionListener {
public void actionPerformed (ActionEvent e) {
System.out.println("The JButton Works!");
Body.calc();
}
}
public class postActionEvent {
String heightget = heighttf.getText();
int height = Integer.parseInt(heightget);
}
public class heighttfhandler implements ActionListener {
public void actionPerformed (ActionEvent e) {
String heightget = heighttf.getText();
int height = Integer.parseInt(heightget);
System.out.println("Hello" + height);

}
}

private class weighttfhandler implements ActionListener {
public void actionPerformed (ActionEvent e) {
if (e.getSource() == weighttf) {
int weight =
Integer.parseInt(weighttf.getText().trim());
System.out.println("" + weight);
}
}
}
}

Code:

bodymassindex .java
package bmi;

import javax.swing.*;
import java.util.*;

public class bodymassindex extends Observable {
private void GUI();
private int height;
private int weight;
private int bmi;
private char wv;
private String heightString;


public bodymassindex () {
super();

height = 0;
weight = 0;
bmi = 0;
}

public void calc() {
getHeight();
getWeight();
getbmi();
setwvtf();
setChanged();
notifyObservers();
}

public int getHeight() {
height = GUI.postActionEvent.height;
return height;
}

public int getWeight() {

return weight;
}
public int getbmi() {
getHeight();
getWeight();
bmi = weight + height;
return bmi;
}
public char setwvtf() {
return wv;
}
}

I get an error:

Code:

non-static variable height cannot be referenced from a static context at line 33 (33:34)

Thanks.

hardwired · #2 (**permalink**) 08-01-2007, 11:25 PM

The Observer/Observable can become awkward to implement because of having to extend Observable. I suggest either not using it or trying a PropertyChangeListener approach. If you can do without it you could have the gui update the Body through/via its listeners.

Code:

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.util.*;
//import javax.*;
//import bmi.GUI.*;

public class BMITest extends JFrame {
    //Declare JTextFields
    private JTextField heighttf;
    private JTextField weighttf;
    private JTextField bmitf;
    private JTextField wvtf;
    private Body body;
//    private static int height;

    //Default Constructor
    public BMITest(Body body) {
        super();
        this.body = body;
        Container contents = getContentPane();

        //Create JPanels
        JPanel panel1 = new JPanel();
        panel1.setLayout(new BorderLayout());

        JPanel panel2 = new JPanel();
        panel2.setLayout(new GridLayout (1, 3, 5, 20));

        JPanel panel3 = new JPanel();
        panel3.setLayout(new GridLayout (1, 3, 5, 20));

        JPanel panel4 = new JPanel();
        panel4.setLayout(new GridLayout (1, 2, 5, 20));

        //Instantiate JTextFields
        // These local declarations hide the member variables.
        // Remove the declarations so the statements will/can
        // instantiate the member variables.
        /*JTextField*/ heighttf = new JTextField();
        /*JTextField*/ weighttf = new JTextField();
        /*JTextField*/ bmitf = new JTextField();
        /*JTextField*/ wvtf = new JTextField();

        //Set Editable to False on bmitf and wvtf
        heighttf.setEditable(true);
        weighttf.setEditable(true);
        bmitf.setEditable(false);
        wvtf.setEditable(false);

        //Create JLabels
        JLabel heightl = new JLabel("Height");
        JLabel weightl = new JLabel("Weight");
        JLabel bmil = new JLabel("BMI");

        //Create JButtons
        JButton calcb = new JButton("Calculate");

        //Add Panels to Panel1
        panel1.add(panel2,BorderLayout.NORTH);
        panel1.add(panel3,BorderLayout.CENTER);
        panel1.add(panel4,BorderLayout.SOUTH);

        //Add buttons, text fields, etc to panel2
        panel2.add(heightl);
        panel2.add(weightl);
        panel2.add(bmil);

        //Add buttons, text fields, etc to panel3
        panel3.add(heighttf);
        panel3.add(weighttf);
        panel3.add(bmitf);

        //Add buttons, text fields, etc to panel4
        panel4.add(wvtf);
        panel4.add(calcb);

        //Set Text Align to Center
        weighttf.setHorizontalAlignment(JTextField.CENTER);
        heighttf.setHorizontalAlignment(JTextField.CENTER);
        bmitf.setHorizontalAlignment(JTextField.CENTER);
        wvtf.setHorizontalAlignment(JTextField.CENTER);

        //Resgister Listener
        weighttf.addActionListener(new weighttfhandler());
        heighttf.addActionListener(new heighttfhandler());
        calcb.addActionListener(new calcbuttonhandler());

        //Frame information
        contents.add(panel1);
        setTitle("BMI Calculator");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setSize(200, 100);
        setVisible(false);
        bmitf.setText("" + body.getbmi());
    }

    private class calcbuttonhandler implements ActionListener {
        public void actionPerformed (ActionEvent e) {
            //System.out.println("The JButton Works!");
            updateBody();
            int bmIndex = body.getbmi();
            System.out.println("bmi = " + bmIndex);
            bmitf.setText(String.valueOf(bmIndex));
        }
    }

    public class heighttfhandler implements ActionListener {
        public void actionPerformed (ActionEvent e) {
            String heightget = heighttf.getText();
            int height = Integer.parseInt(heightget);
            System.out.println("Hello" + height);
            body.setHeight(height);
        }
    }

    private class weighttfhandler implements ActionListener {
        public void actionPerformed (ActionEvent e) {
            if (e.getSource() == weighttf) {
                int weight =
                    Integer.parseInt(weighttf.getText().trim());
                System.out.println("" + weight);
                body.setWeight(weight);
            }
        }
    }

    private void updateBody() {
        String w = heighttf.getText();
        int weight = w.equals("") ? 0 : Integer.parseInt(w);
        body.setHeight(weight);
        String h = weighttf.getText().trim();
        int height = h.equals("") ? 0 : Integer.parseInt(h);
        body.setWeight(height);
    }

    public static void main(String[] args) {
        BMITest test = new BMITest(new Body());
        test.setLocation(300,200);
        test.setVisible(true);
    }
}

class Body {
    private int height;
    private int weight;
    private int bmi;
    private char wv;
    private String heightString;

    public Body() {
        height = 0;
        weight = 0;
        bmi = 0;
    }

    public int getHeight() { return height; }

    public int getWeight() { return weight; }

    public void setHeight(int height) { this.height = height; }

    public void setWeight(int weight) { this.weight = weight; }

    public int getbmi() {
        bmi = weight + height;
        return bmi;
    }

    public char setwvtf() {
        return wv;
    }
}