Challenge exercise Java

Question

I need help with problem 41.



Exercise 3.40 Assume a class Tree has a field of type Triangle called leaves and a field of type Square called trunk. The constructor of Tree takes no parameters and its constructor creates the Triangle and Square objects for its fields. Using the figures project from Chapter 1, create a simple Tree class to fit this description. You do not need to define any methods in the class and the shapes do not have to be made visible.

Exercise 3.41 Challenge Exercise Complete the Tree class described in the previous exercise, by having the constructor move the trunk square beneath the leaves triangle and then make both shapes visible. Do this by defining a method in the Tree class called setup and include a call to this method in the constructor of Tree. Change the size of the triangle so that it looks more like the leaves of a fir tree growing from the trunk.

Bellow is the code for the "triangle" in the figures project from chapter one.

package figures;

import java.awt.*;

/**
* A triangle that can be manipulated and that draws itself on a canvas.
*
* @author Michael Kölling and David J. Barnes
* @version 2011.07.31
*/

public class Triangle
{
private int height;
private int width;
private int xPosition;
private int yPosition;
private String color;
private boolean isVisible;

/**
* Create a new triangle at default position with default color.
*/
public Triangle()
{
height = 60;
width = 70;
xPosition = 210;
yPosition = 140;
color = "green";
isVisible = false;
}

/**
* Make this triangle visible. If it was already visible, do nothing.
*/
public void makeVisible()
{
isVisible = true;
draw();
}

/**
* Make this triangle invisible. If it was already invisible, do nothing.
*/
public void makeInvisible()
{
erase();
isVisible = false;
}

/**
* Move the triangle a few pixels to the right.
*/
public void moveRight()
{
moveHorizontal(20);
}

/**
* Move the triangle a few pixels to the left.
*/
public void moveLeft()
{
moveHorizontal(-20);
}

/**
* Move the triangle a few pixels up.
*/
public void moveUp()
{
moveVertical(-20);
}

/**
* Move the triangle a few pixels down.
*/
public void moveDown()
{
moveVertical(20);
}

/**
* Move the triangle horizontally by 'distance' pixels.
*/
public void moveHorizontal(int distance)
{
erase();
xPosition += distance;
draw();
}

/**
* Move the triangle vertically by 'distance' pixels.
*/
public void moveVertical(int distance)
{
erase();
yPosition += distance;
draw();
}

/**
* Slowly move the triangle horizontally by 'distance' pixels.
*/
public void slowMoveHorizontal(int distance)
{
int delta;

if(distance < 0)
{
delta = -1;
distance = -distance;
}
else
{
delta = 1;
}

for(int i = 0; i < distance; i++)
{
xPosition += delta;
draw();
}
}

/**
* Slowly move the triangle vertically by 'distance' pixels.
*/
public void slowMoveVertical(int distance)
{
int delta;

if(distance < 0)
{
delta = -1;
distance = -distance;
}
else
{
delta = 1;
}

for(int i = 0; i < distance; i++)
{
yPosition += delta;
draw();
}
}

/**
* Change the size to the new size (in pixels). Size must be >= 0.
*/
public void changeSize(int newHeight, int newWidth)
{
erase();
height = newHeight;
width = newWidth;
draw();
}

/**
* Change the color. Valid colors are "red", "yellow", "blue", "green",
* "magenta" and "black".
*/
public void changeColor(String newColor)
{
color = newColor;
draw();
}

/**
* Draw the triangle with current specifications on screen.
*/
private void draw()
{
if(isVisible) {
Canvas canvas = Canvas.getCanvas();
int[] xpoints = { xPosition, xPosition + (width/2), xPosition - (width/2) };
int[] ypoints = { yPosition, yPosition + height, yPosition + height };
canvas.draw(this, color, new Polygon(xpoints, ypoints, 3));
canvas.wait(10);
}
}

/**
* Erase the triangle on screen.
*/
private void erase()
{
if(isVisible) {
Canvas canvas = Canvas.getCanvas();
canvas.erase(this);
}
}
}

Answer 1

Exercise 3.40: The question asks you to create a Tree class, which has only 2 fields - leaves (Triangle class) and trunk (Square class). So first let us build a Tree class and a constructor inside it.

____________________Step 1_________________

class Tree(){

public Tree(){ //This is the constructor

}

}

__________________________________________

Now, we need to declare 2 fields, leaves and trunk, in the Tree class. We will instantiate the 2 variables inside the constructor.

____________________Step 2_________________

class Tree(){

Square trunk;

Triangle leaves;

public Tree(){. //This is the constructor

trunk = new Square(); //object created

leaves = new Triangle(); //object created

}

}

__________________________________________

Now we are done. We did not take any parameters for the constructor.

Exercise 3.41:

NOTE: Since the question does not provide code for the square class. So the names of the square methods are unknown. I have answered how to apply the triangle methods and assumed the names for square methods.

Let us first create a method called setup

____________________Step 1_________________

class Tree(){

Square trunk;

Triangle leaves;

public Tree(){. //This is the constructor

trunk = new Square(); //object created

leaves = new Triangle(); //object created

}

public void setup(){

}

}

__________________________________________

Now, we will use the changeSize method to make the fig leaves look bigger, move their position, and then draw them. Similarly, we only need to display the trunk without changing anything.

We will also call the setup method in the constructor.

____________________Step 2_________________

class Tree(){

Square trunk;

Triangle leaves;

public Tree(){. //This is the constructor

trunk = new Square(); //object created

leaves = new Triangle(); //object created

setup(); // Calling the setup method

}

public void setup(){

leaves.changeSize(125,100); //We will make the fig leaves big

leaves.draw(); // We need to draw them first in order to move them

leaves.moveHorizontal(100); //Please move accordingly to the size and position of trunk

leaves.moveVertical(-150); //Please move accordingly to the size and position of trunk

leaves.makeVisible(); // Lastly this will display the fig leaf

//ASSUMING that trunk's method name is draw and makeVisible

trunk.draw();

trunk.makeVisible();

}

}

__________________________________________

Feel free to ask me any questions if you're still unclear.