littleprime.java

打印质数的Java源代码

//输出小于等于用户输入之自然数的所有素数
import java.io.*;
public class LittlePrime
{
	public static void main(String args[]) throws IOException
	{
		System.out.print("Please input a natural number: ");
		BufferedReader in = new BufferedReader (new InputStreamReader(System.in));
		String s = in.readLine();//得到输入
		int n = Integer.parseInt(s);
		if(n==1)
			System.out.println("There is no prime number!");
		else
		{
			System.out.print("The prime number is: ");
			for(int i=1;i<=n;i++)
			{
				if(IsPrimeNum(i)==1)
				System.out.print(i+" ");
			}
			System.out.println();
		}
	}
	static int IsPrimeNum(int a)	//判断一个自然数是否是素数
	{
		if(a==1) return 0;
		else if(a==2 || a==3)
			return 1;
		else
		{
			for(int i=2;i<=a/2;i++)
			{
				if(a%i==0)
				return 0;
				continue;
			}
			return 1;
		}
	}
}