[tex]answer[/tex]

Sure! Here's a full program to find the factorial of a number using the four forms of methods in BlueJ:

```java

public class Factorial {

// Method 1: Non-recursive method

public static int factorialNonRecursive(int n) {

int result = 1;

for (int i = 1; i <= n; i++) {

result *= i;

}

return result;

}

// Method 2: Recursive method

public static int factorialRecursive(int n) {

if (n == 0 || n == 1) {

return 1;

}

return n * factorialRecursive(n - 1);

}

// Method 3: Tail-recursive method

public static int factorialTailRecursive(int n, int result) {

if (n == 0 || n == 1) {

return result;

}

return factorialTailRecursive(n - 1, n * result);

}

// Method 4: Iterative method

public static int factorialIterative(int n) {

int result = 1;

while (n > 1) {

result *= n;

n--;

}

return result;

}

public static void main(String[] args) {

int num = 5;

int result1 = factorialNonRecursive(num);

System.out.println("Factorial (Non-recursive): " + result1);

int result2 = factorialRecursive(num);

System.out.println("Factorial (Recursive): " + result2);

int result3 = factorialTailRecursive(num, 1);

System.out.println("Factorial (Tail-recursive): " + result3);

int result4 = factorialIterative(num);

System.out.println("Factorial (Iterative): " + result4);

}

}

```

To run this program in BlueJ, follow these steps:

1. Open BlueJ and create a new project.

2. Create a new class called "Factorial".

3. Copy and paste the above code into the "Factorial" class.

4. Click on the "Compile" button in BlueJ to compile the code.

5. Right-click on the "Factorial" class and select "void main(String[] args)" to run the program.

6. The program will calculate and display the factorial of the number 5 using the four different methods.

The output will be:

```

Factorial (Non-recursive): 120

Factorial (Recursive): 120

Factorial (Tail-recursive): 120

Factorial (Iterative): 120

```

Each method will calculate the factorial of the given number (5 in this case) and display the result.