Inheritance using extend class

[vigalegiadom]

Hello forum,

I have been trying to run the code below using inheritance keyword "extends" from command prompt in windows xp, but I get the error message
C:\Program Files\Java\jdk1.7.0_03\bin>javac rect.java
rect.java:65: error: non-static variable this cannot be referenced from a static
context
triangle tri=new triangle();

Can someone debug this using command prompt in windows xp, the complete program is below:

/*
* To change this template, choose Tools | Templates
* and open the template in the editor.
*/
package inheritprog;
class rect
{
protected double h;
protected double b;
public void seth(double h)
{
this.h=h;
}
public void setb(double b)
{
this.b=b;
}
public double geth()
{
return h;
}
public double getb()
{
return b;
}
public double arearect()
{
return h*b;
}

class triangle extends rect
{
public double areatri()
{
return(1./2.*h*b);
}

}

/**
*
* @author HP
*/


/**
*
* @author user
*/
//public class Inheritprog {

/**
* @param args the command line arguments
*/
public static void main(String[] args) {
/**
* @param args the command line arguments
*/

// TODO code application logic here
rect rec=new rect();
rec.seth(10);
rec.setb(5);
System.out.println("Area of a rectangle= "+rec.arearect());
triangle tri=new triangle();
tri.seth(10);
tri.setb(8);
System.out.println("Area of a triangle= "+tri.areatri());
}


}





Thanks

[DarrylBurke]

Moved from Advanced Java.

Please go through Guide For New Members and BB Code List - Java Programming Forum and edit your post accordingly.

db

[Jingoism]

You had a few problems.

First off when you extend a class you must have the method in your subclass implemented in the superclass.

Secondly I just moved your triangle class outside the rect class, and everything seems to work fine now.

Take my advice with a grain of salt though as I am still a newbie to Java... might wanna have an actual expert chime in.

class rect {
	protected double h;
	protected double b;
	public void seth(double h)
	{
		this.h=h;
	}
	public void setb(double b)
	{
		this.b=b;
	}
	public double geth()
	{
		return h;
	}
	public double getb()
	{
		return b;
	}
	public double arearect()
	{
		return h*b;
	}
	public double areatri()
	{
		//This must exist in the superclass
		return(1./2.*h*b);
	}
	

	/**
	 *
	 * @author HP
	 */


	/**
	 *
	 * @author user
	 */
	//public class Inheritprog {

	/**
	 * @param args the command line arguments
	 */
	public static void main(String[] args) {
		/**
		 * @param args the command line arguments
		 */

		// TODO code application logic here
		rect rec=new rect();
		rec.seth(10);
		rec.setb(5);
		System.out.println("Area of a rectangle= "+rec.arearect());
		triangle tri=new triangle();
		tri.seth(10);
		tri.setb(8);
		System.out.println("Area of a triangle= "+tri.areatri());
	}
	
}

class triangle extends rect {
	@Override
	public double areatri()
	{
		System.out.println("Calling from triangle");
		return(1./2.*h*b);
	}

}