filling an array list with values

[nathang1392]

im working on a program that calculates the trajectory of an object given its launch speed and its launch angle. i have two array lists. one for speed, and one for angle. i also have a method that given the speed and angle can calculate the distance that the object will go. i have everything i need besides what actually does the calculations, it gets kind of confusing at this point. i have to take each speed and angle and get the distance to fill a table. i made a new array called distance, what is confusing me though is how to take each value and calculate and so on and so on. i attached a picture of the table so it would be easy to get an idea of what i was talking about. i have been struggling trying to figure this out for the last few days. if you guys can help me figure this out it would be very appreciated.



/**
* Write a description of class Catapult here.
*
* @author (your name)
* @version (a version number or a date)
*/
import static java.lang.Math.*;
public class Catapult
{
public double launchSpeed, launchAngle, distanceFeet, distanceMeters, distance, speed, angle;
public static final double accelerationDueToGravity = 9.8, speedFeetFactor = 3.28;






public Catapult(double speed, double angle)
{


}



public void distanceMeters()
{

distanceMeters = pow(speed, 2) * Math.sin(2 * toRadians(angle)) / accelerationDueToGravity;

}

public void distanceFeet()
{
distanceFeet = distance * speedFeetFactor;

}
}



/**
* Write a description of class CatapultTester here.
*
* @author (your name)
* @version (a version number or a date)
*/
import java.util.ArrayList;
public class CatapultTester
{
public static void main(String[] args)
{
ArrayList<Integer> speed = new ArrayList<Integer>();
speed.add(new Integer(20));
speed.add(new Integer(25));
speed.add(new Integer(30));
speed.add(new Integer(35));
speed.add(new Integer(40));
speed.add(new Integer(45));
speed.add(new Integer(50));


ArrayList<Integer> angle = new ArrayList<Integer>();
angle.add(new Integer(25));
angle.add(new Integer(30));
angle.add(new Integer(35));
angle.add(new Integer(40));
angle.add(new Integer(45));
angle.add(new Integer(50));
angle.add(new Integer(55));





ArrayList<Double> distance = new ArrayList<Double>();
for(int i = 0; i < angle.size(); i ++)
{




}


//print header
System.out.println(" Projectile Distance (feet)");
System.out.println(" MPH \t 25 deg \t 30 deg \t 35 deg \t 40 deg \t 45 deg \t 50 deg \t 55 deg");
System.out.println("================================================== ================================================== ===========");





}
}

[dwhitney67]

It seems that for each velocity, you need to test each at different angles. Thus I would suspect that you need nested for-loops, to iterate through each of the arrays you have.

Something like:


for i := [0 ... array1.size)
{
for j := [0, array2.size)
{
// do something with array1[i] and array2[j]
}
}

Note, the code above is an attempt at pseudo-code.

[nathang1392]

thats mostly the part i dont understand, i mean i know thats what i need to do, but im having trouble getting how to actually perform it. im not really too familiar with array list and how they work. i know that i need to test each velocity against each angle, but...](*,)

basically what im trying to do is have a for loop that takes each velocity and then a for loop inside that takes each angle and plugs them into my method, but i dont know how to actually construct the part that tells the methods which numbers to use.

im having trouble explaining my problem, sorry.

[dwhitney67]

Since you are developing Java applications, the website detailing the API is a must-have; thus bookmark this URL:
http://java.sun.com/javase/6/docs/api/

For the ArrayList, click here:
http://java.sun.com/javase/6/docs/api/java/util/ArrayList.html

You are probably going to want to familiarize yourself with:
add(), get(), and size().

P.S. I can see from your code that you already know about add().

[nathang1392]

alright, im trying to follow your direction. i looked at the api's and i tried to familiarize myself. i got some code together, but im not sure it is right.


ArrayList<Double> distance = new ArrayList<Double>();
for(int i = 0; i < angle.size(); i ++)
{
for int j = 0; j < speed. size(); j++)
{
distance[i][j] = catapult.getDistance(speed[i], angle[j])
}
}
i dont know if this is the right track, but im getting compiler errors.

[PaulM1985]

Where do you get your compiler errors, can you post the full code.

Paul

[nathang1392]

/**
* Write a description of class Catapult here.
*
* @author (your name)
* @version (a version number or a date)
*/
import static java.lang.Math.*;
public class Catapult
{
public double launchSpeed, launchAngle, distanceFeet, distanceMeters, distance, speed, angle;
public static final double accelerationDueToGravity = 9.8, speedFeetFactor = 3.28;






public Catapult(double speed, double angle)
{


}



public void distanceMeters()
{

distanceMeters = pow(speed, 2) * Math.sin(2 * toRadians(angle)) / accelerationDueToGravity;

}

public void distanceFeet()
{
distanceFeet = distance * speedFeetFactor;

}
}


/**
* Write a description of class CatapultTester here.
*
* @author (your name)
* @version (a version number or a date)
*/
import java.util.ArrayList;
public class CatapultTester
{
public static void main(String[] args)
{
ArrayList<Integer> speed = new ArrayList<Integer>();
speed.add(new Integer(20));
speed.add(new Integer(25));
speed.add(new Integer(30));
speed.add(new Integer(35));
speed.add(new Integer(40));
speed.add(new Integer(45));
speed.add(new Integer(50));


ArrayList<Integer> angle = new ArrayList<Integer>();
angle.add(new Integer(25));
angle.add(new Integer(30));
angle.add(new Integer(35));
angle.add(new Integer(40));
angle.add(new Integer(45));
angle.add(new Integer(50));
angle.add(new Integer(55));





ArrayList<Double> distance = new ArrayList<Double>();
for(int i = 0; i < angle.size(); i ++)
{
for(int j = 0; j < speed. size(); j++)
{
distance[i][j] = catapult.getDistance(speed[i], angle[j];
}
}







//print header
System.out.println(" Projectile Distance (feet)");
System.out.println(" MPH \t 25 deg \t 30 deg \t 35 deg \t 40 deg \t 45 deg \t 50 deg \t 55 deg");
System.out.println("================================================== ================================================== ===========");





}
}

i get ")" expected on my line that is inside of my j loop. if you can help it would be very very appreciated.

[nathang1392]

sorry the ) was needed. i fixed that. now im getting that array is required, but arraylist is found.

[dwhitney67]

You need to add distance values to your 'distance' array; I do not believe you can set them manually as you have shown earlier.

Consider the following:


ArrayList<Double> distance = new ArrayList<Double>();

for (int i = 0; i < angle.size(); ++i)
{
for (int j = 0; j < speed.size(); ++j)
{
Double dist = new Double(catapult.getDistance(speed[i], angle[j]));

distance.add(dist);
}
}

To access the values in the 'distance' array list, you will need to perform some basic arithmetic so that you can associate the row/column for your table. Think of your angle index as being the row number, and the speed index as your column number.

Thus, to print the data of your table:


for (int i = 0; i < angle.size(); ++i)
{
for (int j = 0; j < speed.size(); ++j)
{
System.out.print(distance.get((i * speed.size()) + j) + " ");
}
System.out.println();
}

Of course, the code above lacks the pretty table to show the relationship between MPH and Angle, but I'll leave that up to you to do.

P.S. It's been a while since I did Java programming; you may need to convert the Double values in the distance array using toString() before you can print them.

P.S. #2 A lot of your compiler errors are due to poor syntax; pay careful attention when you write code.

[nathang1392]

im still getting the same problem with the first part of your code, array required, but arraylist found

[dwhitney67]

Just take a look at the following:


import java.util.ArrayList;
import java.lang.Math.*;

public class Catapult
{
private double speed;
private double angle;

private static final double GRAVITY_ACCELERATION = 9.8;
private static final double SPEED_FEET_FACTOR = 3.28;

public Catapult(double speed, double angle)
{
this.speed = speed;
this.angle = angle;
}

public double getDistance()
{
return Math.pow(speed, 2) * Math.sin(2.0 * Math.toRadians(angle)) / GRAVITY_ACCELERATION;
}

public static void main(String[] args)
{
ArrayList<Double> speed = new ArrayList<Double>();
speed.add(new Double(20));
speed.add(new Double(25));
speed.add(new Double(30));
speed.add(new Double(35));
speed.add(new Double(40));
speed.add(new Double(45));
speed.add(new Double(50));

ArrayList<Double> angle = new ArrayList<Double>();
angle.add(new Double(25));
angle.add(new Double(30));
angle.add(new Double(35));
angle.add(new Double(40));
angle.add(new Double(45));
angle.add(new Double(50));
angle.add(new Double(55));

//ArrayList<Double> distance = new ArrayList<Double>();

System.out.println(" Projectile Distance (feet)");
System.out.println(" MPH \t 25 deg \t 30 deg \t 35 deg \t 40 deg \t 45 deg \t 50 deg \t 55 deg");

for(int i = 0; i < angle.size(); ++i)
{
System.out.print("\n" + speed.get(i) + "\t");

for(int j = 0; j < speed.size(); ++j)
{
// A Catapult object needs to be constructed!
Catapult cat = new Catapult(speed.get(i), angle.get(j));
Double dist = new Double(cat.getDistance());

//distance.add(dist);
//System.out.print(distance.get((i*speed.size()) + j) + "\t");

System.out.print(dist + "\t");
}
}
System.out.println();
}
}


If you require the 'distance' array, then uncomment what I have commented-out above.

Also, do some research on how you can set the precision on the double values so that you yield a result that has no more, and no less, precision than your input data.

[nathang1392]

thanks so much. it makes alot more sense. your a java pro.