Write a class named gastank containing:
an instance variable named amount of type double, initialized to 0.
a method named addgas that accepts a parameter of type double.
the value of the amount instance variable is increased by the value of the parameter.
a method named usegas that accepts a parameter of type double.
the value of the amount instance variable is decreased by the value of the parameter.
a method named getgaslevel that accepts no parameters.
getgaslevel returns the value of the amount instance variable.

The answer to this question can be given as:

Class definition:

public class GasTank   //define class GasTank

{

private double amount = 0;  //define variable.

public void addGas(double x)  //define function addGas.

{

amount=amount+x;   //calculate value.

}

public void useGas(double x)  //define function useGas.

{

amount=amount-x;   //calculate value.

}

public double getGasLevel()  //define function getGasLevel

{

return amount;   //return value.

}

}

Explanation:

The description of the above class definition can be given as:

In the class definition first we define a class that is "GasTank". In this class we define a variable that is amount the datatype of this variable is double that is used to store real or decimal values.Then we define three function that is  addGas(), useGas() and getGasLevel(). addGas() and useGas() function does not return any value and in both function we pass variable x as a parameter that calculate there value and the getGasLevel() function will return amount variable value.

//. Program is written in Java Programming Language

// Comments are used for explanatory purpose

// Program starts here

// import required libraries

import java.swing.JApplet;

import java.awt.*;

// Declare class as

public class DrawGraphics extends JApplet

{

//.Assume the following values for width, height and area of the shape

final int area= 150 ;

final int width = 100, height = 50;

{

//Draw a Rectangle around the applet's display area starting from 5,15

g.drawRect( 5,15, area-1, area-1 );

//Draw the current string inside the rectangle

g.drawRect( area/2 - width/2 , area/2 - height/2, width, height );

}

}