Question

Using Java:

Create a class called MyNumber with an integer private attribute.

Create a constructor that defines an integer parameter to set the private integer attribute.

Create a setter that validates the attribute does not accept a value lower than 2 or the method will throw a IllegalArgumetException.

Create a getter to return the private integer attribute value.

Define a public method that is called isPrime() that returns a boolean and implements the Sieve of Eratosthenes method.

Define a public method that is called numberOfPrimes() that returns the number of prime numbers between 2 and the private attribute value.

Demonstrate this object in a main method that allows the user to interact with all the public methods of your class.

Answer 1

Refer to code snippet below. Output is attached.

public class MyClass {
        private int n;
        public MyClass() {}
        public MyClass(int n) throws Exception //param constructor
        {
                if(n<2)
                {
                        throw new IllegalArgumentException("Number is less than 2");
                }
                else
                {
                        this.n = n;
                }
        }
        public void setNum(int n) throws Exception //setter method
        {
                if(n<2)
                {
                        throw new IllegalArgumentException("Number is less than 2");
                }
                else
                {
                        this.n = n;
                }
        }
        public int getNum()//getter method
        {
                return this.n;
        }
        public boolean isPrime() //O(root(n))
        {
                for(int i = 2; i<Math.sqrt(this.n); i++)
                {
                        if(this.n%i == 0)
                        {
                                return false;
                        }
                }
                return true;
        }
        public int numberOfPrimes() //implements SOE
    {  
        boolean prime[] = new boolean[n+1]; 
        int count = 0;
        for(int i=0;i<this.n;i++) 
            prime[i] = true; 
          
        for(int p = 2; p*p <=this.n; p++) 
        { 
            
            if(prime[p] == true) 
            { 
                for(int i = p*p; i <= this.n; i += p) 
                    prime[i] = false; 
            } 
        }  
        for(int i = 2; i <= this.n; i++) 
        { 
            if(prime[i] == true) 
                count++; 
        } 
        return count;
    }
        public static void main(String[] args) throws Exception{
                MyClass cl = new MyClass(20);
                System.out.println(cl.isPrime());
                System.out.println(cl.numberOfPrimes());
                System.out.println(cl.getNum());
        }
}

Output:

false
8
20