findprime.java

查找一定范围内的素数的算法

import java.io.*;
import java.applet.*;
import java.awt.*;
import java.awt.event.*;
public class FindPrime extends Applet implements ActionListener {
       Label prompt;
       Button btn;
       TextField input1, input2;
       int a=0, b=0, k=0;
       int []c = new int[100];
       public void init(){
            prompt = new Label("请输入上下限:");
            input1 = new TextField(5);
            input2 = new TextField(5);
            btn = new Button("素数");
            add(input1);
            add(input2);
            add(btn);    
            add(prompt);
            btn.addActionListener(this);
       }


       public void paint(Graphics g){
            int j=1;
            int m=1;
            for(int i=1; i<=k-1; i++){
                g.drawString(Integer.toString(c[i]), 20*m, 60+20*j);//20*i的i改为m
                m++;
                if(i%10==0){
		    j++;
                    m=1;
                 }
            }
       }


       public void actionPerformed(ActionEvent e){
             a = Integer.parseInt(input1.getText());
             b = Integer.parseInt(input2.getText());
       loop: for(int i=a; i<=b; i++){
                for(int j=2;j<=Math.sqrt(i);j++)
		    if(i%j==0) continue loop;
                c[k]=i;
                k++;
             }          
             prompt.setText(" 所有素数:"); 
             repaint();
       }
}