macOS java homework, I am stuck

letsdiscussit · Apr 5, 2008

I take a course at univ in Java for beginners and we got an assignment and I just don't know how to solve it.

I programed an array of integers that get sorted and than printed. Now I want to produce the same thing with random numbers using "import java.util.Random". How I am going to do that?

package Assignment1.sorting;

import java.awt.Graphics;
import java.applet.Applet;

public class Assignment1 extends Applet {

int a[] = {55, 25, 66, 45, 8, 10, 12, 89, 68, 37};

public void paint(Graphics g) {
print(g, "Data items in original order", a, 25, 25);

sort(a);

print(g, "Data items in ascending order", a, 25, 55);

}

public void sort(int b[]) {
int temp;
for (int i = 0; i < b.length - 1; i++) {
for (int j = i + 1; j < b.length; j++) {
if (b > b[j]) {
temp = b;
b = b[j];
b[j] = temp;
}
}

}
}

public void print(Graphics g, String head, int b[], int x, int y) {
g.drawString(head, x, y);
x += 15;
y += 15;
for (int i = 0; i < b.length; i++) {
g.drawString(String.valueOf(b), x, y);
x += 20;
}
}
}

stevento · Apr 5, 2008

if you want a random int i wouldn't bother with importing that i would do this

Code:

int r = (int) (10.0* Math.rand());

and that will give you a random number from 0 to 9

sord · Apr 5, 2008

You need to create a Random object, and then look at the documentation here:
http://java.sun.com/j2se/1.4.2/docs/api/java/util/Random.html

This shows you the methods you can call for a Random object.

SC68Cal · Apr 5, 2008

Code:

Random generator = new Random();

generator.nextInt();

letsdiscussit · Apr 6, 2008

Thanks for your replies. I am still doing something wrong, in bold I highlited the are, doesn't except the variable a. How I am going to do so?

package assignment2;

import java.awt.Graphics;
import java.applet.Applet;
import java.util.Random;

public class Assignment2 extends Applet {

public void fill( int max ) {
final int MAX = 6;

Random generator = new Random();

int[] a = new int[MAX];

for(int k = 0; k < MAX; k++){

a[k] = generator.nextInt(100) + 1;

}
}

// What am I doing wrong that it cannot find variable a??

public void paint(Graphics g) {
print(g, "Data items in original order", a, 25, 25);

sort(a);

print(g, "Data items in ascending order", a, 25, 55);

}

public void sort(int b[]) {
int temp;
for (int i = 0; i < b.length - 1; i++) {
for (int j = i + 1; j < b.length; j++) {
if (b > b[j]) {
temp = b;
b = b[j];
b[j] = temp;
}
}

}
}

public void print(Graphics g, String head, int b[], int x, int y) {
g.drawString(head, x, y);
x += 15;
y += 15;
for (int i = 0; i < b.length; i++) {
g.drawString(String.valueOf(b), x, y);
x += 20;
}
}
}

eharley · Apr 6, 2008

letsdiscussit said:
Thanks for your replies. I am still doing something wrong, in bold I highlited the are, doesn't except the variable a. How I am going to do so?

You're defining a inside the fill() method. So it's only accessible to that method. If you want other methods in your class to be able to get to it, you need to declare it in your class like this:

Code:

public class Assignment2 extends Applet {
	
	final int MAX = 6;
	int[] a = new int[MAX];

	/// ....

letsdiscussit · Apr 6, 2008

thanks Eharley, I almost got it. In two lines, it now says:local variable hides field (highlighted below), what's wrong there?

package assignment2;

import java.awt.Graphics;
import java.applet.Applet;
import java.util.Random;

public class Assignment2 extends Applet {
private int MAX;

int[] a = new int[MAX];
public void fill( int max ) {
//local variable hides field
final int MAX = 6;

Random generator = new Random();
//local variable hides field
int[] a = new int[MAX];

for(int k = 0; k < MAX; k++){

a[k] = generator.nextInt(100) + 1;

}
}

public void paint(Graphics g) {
print(g, "Data items in original order", a, 25, 25);

sort(a);

print(g, "Data items in ascending order", a, 25, 55);

toddburch · Apr 6, 2008

First, you declare MAX as a global private int.

Then, inside a method, you redefine it as a constant.

Then, in your method, you reference it as a constant.

Pick one.

letsdiscussit · Apr 6, 2008

toddburch can u show me how? I thought I refernced it here already as a constant:

private int MAX;

int[] a = new int[MAX];

toddburch · Apr 6, 2008

Your variable a was out of scope. Declaring it as a global, it is no longer out of scope.

Code:

package assignment2;

import java.awt.Graphics;
import java.applet.Applet;
import java.util.Random;



public class Assignment2 extends Applet {

[color=red]final int MAX = 6;
int[] a = new int[MAX];[/color]


public void fill( int max ) {

	Random generator = new Random();

	for(int k = 0; k < MAX; k++){
		a[k] = generator.nextInt(100) + 1;
		}
	}	

	public void paint(Graphics g) {
		print(g, "Data items in original order", a, 25, 25);

		sort(a);

		print(g, "Data items in ascending order", a, 25, 55);

	}

	public void sort(int b[]) {
		int temp;
		for (int i = 0; i < b.length - 1; i++) {
			for (int j = i + 1; j < b.length; j++) {
				if (b[i] > b[j]) {
					temp = b[i];
					b[i] = b[j];
					b[j] = temp;
				}
			}		
		}
	}

	public void print(Graphics g, String head, int b[], int x, int y) {
		g.drawString(head, x, y);
		x += 15;
		y += 15;
		for (int i = 0; i < b.length; i++) {
			g.drawString(String.valueOf(b[i]), x, y);
			x += 20;
		}
	}
}

toddburch · Apr 6, 2008

P.S.

You still need to call the fill() method. Once you do that, it looks good!

letsdiscussit · Apr 6, 2008

How I am going to call the fill () method? If I run the program, it generates only zeros. Please help!

letsdiscussit · Apr 7, 2008

Please help, don't understand where the problem is ...

toddburch · Apr 7, 2008

You have to call the fill() method from paint(), otherwise, your "a" array will have no data in it.

lee1210 · Apr 7, 2008

Code:

package Assignment2;

import java.awt.Graphics;
import java.applet.Applet;
import java.util.Random;



public class Assignment2 extends Applet {

public int[] a = null;

public void fill( int max ) {

        Random generator = new Random();
        a = new int[max];

        for(int k = 0; k < max; k++){
                a[k] = generator.nextInt(100) + 1;
                }
        }

        public void paint(Graphics g) {
                print(g, "Data items in original order", a, 25, 25);

                sort(a);

                print(g, "Data items in ascending order", a, 25, 55);

        }

        public void sort(int b[]) {
                int temp;
                for (int i = 0; i < b.length - 1; i++) {
                        for (int j = i + 1; j < b.length; j++) {
                                if (b[i] > b[j]) {
                                        temp = b[i];
                                        b[i] = b[j];
                                        b[j] = temp;
                                }
                        }
                }
        }

        public void print(Graphics g, String head, int b[], int x, int y) {
                g.drawString(head, x, y);
                x += 15;
                y += 15;
                for (int i = 0; i < b.length; i++) {
                        g.drawString(String.valueOf(b[i]), x, y);
                        x += 20;
                }
        }

        public void init() {
                this.fill(6);
        }

        public Assignment2() { System.out.println("Test!"); }
}

Either init() or the constructor needs to call fill. I have never dealt with applet programming before, but I was finally able to get this to run with appletviewer, displaying what I would expect.

-Lee

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