www.hope.ac.uk faculty of sciences and social sciences hope object oriented programming pie eater...

www.hope.ac.uk Faculty of Sciences and Social Sciences

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Object Oriented ProgrammingPie Eater

Stewart Blakeway

FML 213

[email protected]

0151 291 3113


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What we have done so far

• Created PieEaters world– grid of 8x6– cells of 20px by 20px

• Created PieEater– walks (in direction facing)– records his direction– turns left– turns right


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Aims of the Presentation

• To apply advanced features for PieEater– World Boundaries– Creating Pies– Placing Pies– Random Pies


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What we know - Recap

public class Picture {

private Circle pieEater;

}

public void walk() {

}


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Let’s Create World Boundaries• How can we achieve this?

– How many steps can pieEater take before he leaves his world if facing East?

– How many steps can pieEater take before he leaves his world if facing South?

– How many steps can pieEater take before he leaves his world if facing West?

– How many steps can pieEater take before he leaves his world if facing North?


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Sliding Scales

• Walking East and West

1 2 3 4 5 6 7 8

int stepsx = 1; //PieEater starts in square 1 facing E

We know his direction because each time we turn left or right, it is set.

Each time we walk we add 1 to stepsxIf stepsx < 8 and direction = ‘E’ then walkelse do nothing!


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Pie Eater and Boundariespublic class Picture { private Circle pieEater; int direction = “E”; int stepsx = 1;

}

public void walk() { if ((direction == "E") && (stepsx < 8)) { pieEater.moveHorizontal(40); tail.moveHorizontal(40); stepsx++; } }

Class Exercises – Write the code to

solve the problem with the North and South

boundary issue


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My Solutionpublic class Picture { private Circle pieEater; int direction = “E”; int stepsy = 1;

}

public void walk() { if ((direction == "N") && (stepsy > 1)) { pieEater.moveVertical(-40); tail.moveVertical(-40); stepsy--; } if ((direction == "S") && (stepsy < 6)) { pieEater.moveVertical(40); tail.moveVertical(40); stepsy++; } }


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Let’s Create Some Pies

• How can we achieve this?– We will do this in a method (message)– Remember we have use of the other classes

• Triangle• Square• Circle• Rectangle

This is a complex problem. What do we do with complicated

problems?


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One Piepublic class Picture { private Circle pie;

}

public void drawPie() { pie = new Circle(); pie.changeColor("red"); pie.moveHorizontal(-30); pie.moveVertical(86); pie.changeSize(30); pie.makeVisible(); }

First we create one pie


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Creating Pies Considerations

• We need to ask the user how many pies they want on the grid

• We need to place the pies on the grid at random locations

• Dealing with co-ordinates x and y can be confusing and difficult to work with – easier to work with rows and columns


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public class Picture { int[] gridColumn = new int[8];

Creating Pies initial solution

1. Create a data structure that stores the positions of the 8 columns

public void createPie() { int posx = 86; for (int column=0 ; column<8; column++) { gridColumn[column] = posx; posx=posx+40; } }

What data structure would you use for this?


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public class Picture { int[] gridColumn = new int[8];

Creating Pies initial solution

1. Create a data structure that stores the positions of the 6 rows – the first row position is -30

public void createPie() { int posx = 86; for (int column=0 ; column<8; column++) { gridColumn[column] = posx; posx=posx+40; } }

What data structure would you use for this?


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Creating Pies Initial Solutionpublic class Picture { private Circle pieEater; private Rectangle xLine; private Rectangle yLine; private Rectangle tail;

}

public void createPie() { int posy = -30; for (int row=0 ; row<6; row++) { gridRow[row] = posy; posy=posy+40; } }

My solution


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So far

• we have created a method called– drawPie ()

• draws a pie and places it in the first square

– createPie ()• creates two data structures which contains arrays called

gridRow and gridColumn

• How can we draw a pie using a gridRow and gridColumn value?


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Two Messagespublic void createPie() { int posx = 86; for (int column=0 ; column<8; column++) { gridColumn[column] = posx; posx=posx+40; }

int posy = -30; for (int row=0 ; row<6; row++) { gridRow[row] = posy; posy=posy+40; }

drawPie (gridColumn[4],gridRow[3]); }

public void drawPie(int col, int row) { pie = new Circle(); pie.changeColor("red"); pie.moveHorizontal(col); pie.moveVertical(row); pie.changeSize(30); pie.makeVisible(); }


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Placing Pies Randomly

• Java comes with an inbuilt message that will generate and return a random value

– We could use this to return a random gridColumn– and then again for a random gridRow

row = (int)(Math.random() * 6);

column = (int)(Math.random() * 8);


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Two Messagespublic void createPie() { int posx = 86; for (int column=0 ; column<8; column++) { gridColumn[column] = posx; posx=posx+40; }

int posy = -30; for (int row=0 ; row<6; row++) { gridRow[row] = posy; posy=posy+40; }

int row = (int)(Math.random() * 6);int column = (int)(Math.random() * 8);

drawPie (gridColumn[column],gridRow[row]); }



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Nearly There!

• we have created a method called– drawPie ()

• draws a pie and places it in a square specified

– createPie ()• creates two data structures which are arrays called

gridRow and gridColumn • populates the array with y and x coordinates • creates random values for row and column• passes the gridRow and gridColum array elements

using the random values

What if we want more pies?


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Two Messagespublic void createPie(int numOfPies) { int posx = 86; for (int column=0 ; column<8; column++) { gridColumn[column] = posx; posx=posx+40; }

int posy = -30; for (int row=0 ; row<6; row++) { gridRow[row] = posy; posy=posy+40; } for (int x=1; x < numOfPies ; x++) { int row = (int)(Math.random() * 6); int column = (int)(Math.random() * 8); drawPie (gridColumn[column],gridRow[row]); } }



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So far• Pie Eater

– Created Pie Eater (with a tail)

– Walked

– Turned Left

– Turned Right

– Checked Direction

– Updated Direction

• We have discussed boundaries– Stopped Pie Eater leaving his world

• The pies– Placing them on the grid

– Random location when placing them

– Allowing a specific number of pies


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Next

• Pie Eater encounters a pie– How does pie eater know there is a pie?– How does pie eater eat the pie?

• Should Pie Eater have friends in his world?


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Conclusion

• Pie Eater is a complicated application• Many real world factors have to be accounted for• Object Orient Programming is an excellent

approach for this type of problem

• You are to finish your own PieEater Application– Your project will be compiled– You will demonstrate your project next week (5 min per

person)– Your project will be placed on the website so that you

can impress your friends and your tutors (better work hard)


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Any Questions?

• Next week is a drop in support session – location to be arranged.

www.hope.ac.uk faculty of sciences and social sciences hope object oriented programming pie eater...

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