java编程实现求质数与因式分解代码分享

import java.util.*; 
 
public class Prime {   
  public static int[] findPrimes(final int max) {  
    int[] prime = new int[max+1];  
    ArrayList list = new ArrayList(); 
 
    for(int i = 2; i <= max; i++)  
      prime[i] = 1;  
 
    for(int i = 2; i*i <= max; i++) { // 这边可以改进  
      if(prime[i] == 1) {  
        for(int j = 2*i; j <= max; j++) {  
          if(j % i == 0)  
            prime[j] = 0;  
        }  
      }  
    }  
 
    for(int i = 2; i < max; i++) {  
      if(prime[i] == 1) {  
        list.add(new Integer(i));  
      }  
    } 
     
    int[] p = new int[list.size()]; 
    Object[] objs = list.toArray();  
    for(int i = 0; i < p.length; i++) { 
      p[i] = ((Integer) objs[i]).intValue(); 
    } 
     
    return p; 
  } 
   
  public static void main(String[] args) { 
    int[] prime = Prime.findPrimes(1000); 
     
    for(int i = 0; i < prime.length; i++) { 
      System.out.print(prime[i] + " "); 
    } 
     
    System.out.println(); 
  } 
} 

import java.util.ArrayList; 
 
public class Factor { 
  public static int[] factor(int num) { 
    int[] pNum = Prime.findPrimes(num); 
     
    ArrayList list = new ArrayList(); 
     
    for(int i = 0; pNum[i] * pNum[i] <= num;) {  
      if(num % pNum[i] == 0) {  
        list.add(new Integer(pNum[i])); 
        num /= pNum[i];  
      }  
      else  
        i++;  
    }  
 
    list.add(new Integer(num)); 
     
    int[] f = new int[list.size()]; 
    Object[] objs = list.toArray(); 
    for(int i = 0; i < f.length; i++) { 
      f[i] = ((Integer) objs[i]).intValue(); 
    } 
     
    return f; 
  } 
   
  public static void main(String[] args) { 
    int[] f = Factor.factor(100); 
    for(int i = 0; i < f.length; i++) { 
      System.out.print(f[i] + " "); 
    } 
    System.out.println(); 
  } 
}