判断质数以及求某数以内的质数

package com.maodajun.javaeye5;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

public class SingleWord {
	List list = new ArrayList();
	/**
	 * 将list中的数据求合
	 * @return
	 */
	public int addAll(){
		int all = 0 ;
		String temp = null;
		for(Iterator it = list.iterator();it.hasNext();){
			temp = (String) it.next();
			all += Integer.parseInt(temp);
		}
		return all;
	}
	/**
	 * @deprecated
	 * 已过时方法
	 * 用于判断是否是质数
	 * @param str
	 */
	public void isSingle(String str){
		int tmp = Integer.parseInt(str);
		if(tmp<2){
			return;
		}
		for(int i = 2 ; Math.sqrt(tmp) >=i ; i ++ ){
			if(tmp%i==0){
				return;
			}
		}
		list.add(str);
	}
	/**
	 * 用来找到所有小于str的质数方法
	 * 
	 */
	public void findAllSingle(String str){
		int tmp = Integer.parseInt(str);
		for(int i = 0 ; tmp >i ;i ++){
			isOldSingle(""+i);
		}
	}
	/**
	 * 对输入的数值与已有的数值对比
	 * 看可否被整除.
	 * 
	 * @param str
	 */
	public void isOldSingle(String str){
		int tmp = Integer.parseInt(str);
		if(tmp<2){
			return;	
		}else{
			for(int i = 0 ; list.size()>i ;i++ ){
				int single =Integer.parseInt(list.get(i).toString());
				if(tmp%single ==0){
					return;
				}
			}			
		}
		list.add(str);
	}
	public List getList() {
		return list;
	}
	public void setList(List list) {
		this.list = list;
	}

}

package com.maodajun.javaeye5;

import java.util.ArrayList;
import java.util.List;

import junit.framework.TestCase;

public class SingleWordTest extends TestCase {

	public static void main(String[] args) {
		junit.textui.TestRunner.run(SingleWordTest.class);
	}

	public SingleWordTest(String arg0) {
		super(arg0);
	}

	protected void setUp() throws Exception {
		super.setUp();
	}

	protected void tearDown() throws Exception {
		super.tearDown();
	}

	/*
	 * Test method for 'com.maodajun.javaeye5.SingleWord.addAll()'
	 */
	public void testAddAll() {
		List list = new ArrayList();
		list.add("1");
		list.add("2");
		SingleWord singleword = new SingleWord();
		singleword.setList(list);
		int i = singleword.addAll();
		assertEquals(3,i);
	}
	public void testIsSingle(){
		SingleWord singleword = new SingleWord();
		singleword.isSingle("0");
		assertEquals(0,singleword.getList().size());
		singleword.isSingle("1");
		assertEquals(0,singleword.getList().size());
		singleword.isSingle("4");
		assertEquals(0,singleword.getList().size());
		singleword.isSingle("2");
		assertEquals(1,singleword.getList().size());
		singleword.isSingle("3");
		assertEquals(2,singleword.getList().size());
		singleword.isSingle("13");
		assertEquals(3,singleword.getList().size());
		singleword.isSingle("25");
		assertEquals(3,singleword.getList().size());
		
	}
	public void testIsOldSingle(){
		SingleWord singleword = new SingleWord();
		singleword.isOldSingle("0");
		assertEquals(0,singleword.getList().size());
		singleword.isOldSingle("1");
		assertEquals(0,singleword.getList().size());
		singleword.isOldSingle("2");
		assertEquals(1,singleword.getList().size());
		singleword.isOldSingle("3");
		assertEquals(2,singleword.getList().size());
		singleword.isOldSingle("4");
		assertEquals(2,singleword.getList().size());
		singleword.isOldSingle("5");
		assertEquals(3,singleword.getList().size());
		singleword.isOldSingle("6");
		assertEquals(3,singleword.getList().size());
		
	}
	public void testFindAllSingle(){
		SingleWord singleword = new SingleWord();
		singleword.findAllSingle("10");
		assertEquals(17,singleword.addAll());
		singleword .setList(new ArrayList());
		singleword.findAllSingle("20");
		assertEquals(77,singleword.addAll());

	}

}

来个Erlang版本的：

-module(test).
-export([main/1]).

main(N) ->
    L = calc(N, []),
    S = lists:foldl(fun(X, Total) -> Total+X end, 0, L),
    io:format("质数：~p~n", [L]),
    io:format("总和：~p~n", [S]).
    
%统计某个数以内的所有质数
calc(1, L) -> L;
calc(N, L) ->
    case is_single(N) of
        false -> calc(N-1, L);
        true -> calc(N-1, [N|L])
    end.

%判断是否是质数
is_single(N) -> is_single(N, N-1).
is_single(_N, 1) -> true;
is_single(N, D) when N rem D ==0 -> false;
is_single(N, D) -> is_single(N, D-1).