Java code for factoring a positive integer into a prime factor

Program analysis: to decompose the prime factor of n, the smallest prime number k should be found first, and then completed according to the following steps:
1. If the prime number is exactly equal to n, then the decomposition of the prime factors has been completed, just print it out.

2. If n < > k, but n is divisible by k, print out the value of k and use the quotient of n divided by k as the new positive integer you repeat step 1.

3. If n is not divisible by k, use k+1 as the value of k and repeat step 1.

Program design:

public class exp2{
  public exp2(){}
  public void fengjie(int n){
    for(int i=2;i<=n/2;i++){
      if(n%i==0){
        System.out.print(i+"*");
        fengjie(n/i);
        }
    }
    System.out.print(n);
    System.exit(0);/// Do not omit this sentence, or the result will be wrong 
    }
    public static void main(String[] args){
       String str="";
       exp2 c=new exp2();
       str=javax.swing.JOptionPane.showInputDialog(" Please enter the N Value of (input exit Exit) : ");
       int N;
       N=0;
       try{
           N=Integer.parseInt(str);
           }catch(NumberFormatException e){
             e.printStackTrace();
             }
      System.out.print(N+" Factorization prime factor: "+N+"=");
      c.fengjie(N);
    }  
}