JAVA multiple class file
I just started learning JAVA a couple of days ago and the first program I wrote had two classes in one file. here is the program :
class fib_num {
public int value;
public boolean is_even;
}
class Fibonacci {
/** Print the Fibonacci sequence for values < MAX and mark even numbers with an asterick */
private static final int MAX = 50;
private static final String Title = "The Fibonacci sequence for values less than " + MAX + ":";
private static fib_num[] fib = new fib_num[MAX];//This is actually an array of object
//references to objects of the fib_num class
public static void main(String[] args) {
System.out.println(Title);
//We must initialize each element of the array also !!!!
for (int i = 0; i < fib.length; i += 1) {
fib = new fib_num();
}
int lo = 1, hi = 1;
fib[0].value = lo;
fib[0].is_even = false;
fib[1].value = hi;
fib[1].is_even = false;
for (int i = 2; i < fib.length; i += 1) {
//create the next Fibonacci number and then save the previous Fibonacci number
hi = lo + hi;
lo = hi - lo;
fib.value = hi;
//now indicate if the Fibonacci number is even/odd
if (fib.value % 2 == 0) {
fib.is_even = true;
}else {
fib.is_even = false;
}
}
print (fib);
}
//This method prints an array of Fibonacci numbers
public static void print(fib_num[] array) {
if (array == null || array.length == 0)
throw new IllegalArgumentException();
String mark;
for (int i = 0; array.value < MAX; i += 1) {
if (array.is_even) {
mark = "*";
}else {
mark = "";
}
System.out.println((i + 1) + ": " + array.value + mark);
}
}
}
I ran the program and everything went fine. But today I started to write another program with two classes. However the file will not compile and I get an error about interfacing or something. here is the program:
Note: it's not nearly complete.
class enumerate {
//print out all permutations of a list of integers
public static final int MAX = 4;
public static int[] initialize(int[] nums) {
for (int i = 0; i < nums.length; i++) {
nums = i + 1;
}
return nums;
}
public static void print(int[] nums) {
for (int i = 0; i < nums.length; i++) {
System.out.print(nums);
}
System.out.println("");
}
public static void swap (int[] nums, int i, int j) {
int temp = nums;
nums = nums[j];
nums[j] = temp;
}
public static void main (String[] args) {
int[] list = new int[MAX];
list = initialize(list);
PermutationGenerator x = new PermutationGenerator(5);
}
}
//--
// Systematically generate permutations.
//--
import java.math.BigInteger;
public class PermutationGenerator {
private int[] a;
private BigInteger numLeft;
private BigInteger total;
//--
// Constructor. WARNING: Don't make n too large.
// Recall that the number of permutations is n!
// which can be very large, even when n is as small as 20 --
// 20! = 2,432,902,008,176,640,000 and
// 21! is too big to fit into a Java long, which is
// why we use BigInteger instead.
//-
public PermutationGenerator (int n) {
if (n < 1) {
throw new IllegalArgumentException ("Min 1");
}
a = new int[n];
total = getFactorial (n);
reset ();
}
//
// Reset
//
public void reset () {
for (int i = 0; i < a.length; i++) {
a = i;
}
numLeft = new BigInteger (total.toString ());
}
//
// Return number of permutations not yet generated
//
public BigInteger getNumLeft () {
return numLeft;
}
//
// Return total number of permutations
//
public BigInteger getTotal () {
return total;
}
//--
// Are there more permutations?
//--
public boolean hasMore () {
return numLeft.compareTo (BigInteger.ZERO) == 1;
}
//
// Compute factorial
//
private static BigInteger getFactorial (int n) {
BigInteger fact = BigInteger.ONE;
for (int i = n; i > 1; i--) {
fact = fact.multiply (new BigInteger (Integer.toString (i)));
}
return fact;
}
//--
// Generate next permutation (algorithm from Rosen p. 284)
//--
public int[] getNext () {
if (numLeft.equals (total)) {
numLeft = numLeft.subtract (BigInteger.ONE);
return a;
}
int temp;
// Find largest index j with a[j] < a[j+1]
int j = a.length - 2;
while (a[j] > a[j+1]) {
j--;
}
// Find index k such that a[k] is smallest integer
// greater than a[j] to the right of a[j]
int k = a.length - 1;
while (a[j] > a[k]) {
k--;
}
// Interchange a[j] and a[k]
temp = a[k];
a[k] = a[j];
a[j] = temp;
// Put tail end of permutation after jth position in increasing order
int r = a.length - 1;
int s = j + 1;
while (r > s) {
temp = a[s];
a[s] = a[r];
a[r] = temp;
r--;
s++;
}
numLeft = numLeft.subtract (BigInteger.ONE);
return a;
}
}
I thought the error had somethin to do with only having one class per .java file since the compiler creates a .class file. But how come my first program had two classes and it was OK. Is it b/c the second class was merely a collection of fields, almost like a simple struct in C?
Any help would be appreciated. Thanks
