java邮箱正确性验证

判断邮箱输入是否正确：

import java.util.Arrays;
import java.util.Scanner;
public class Main 
{
	public static void main(String args[]){
        Scanner scan = new Scanner(System.in);
        String str1 = scan.nextLine();
        char[] c1 = str1.toCharArray();
        int a = 0,b=0,c=0;
        for(int i=0;i<str1.length();i++){
        	int num = (int)c1[i];
        	
        	if(num==64){
        		int numl = (int)c1[i-1];
            	int numn = (int)c1[i+1];
            	int numn1 = (int)c1[i+2];
            	int numn2 = (int)c1[i+3];
        		if(((numl>=97&&numl<=122)||(numl>=65&&numl<=90)||(numl>=48&&numl<=57)) && ((numn>=97&&numn<=122)||(numn>=65&&numn<=90)||(numn>=48&&numn<=57))){
        			a=0;
        		}else{
        			a=1;
        		}
        	}
        	if(num == 46){
        		int numl = (int)c1[i-1];
            	int numn = (int)c1[i+1];
            	int numn1 = (int)c1[i+2];
            	int numn2 = (int)c1[i+3];
        		if(numn == 90&&numn1 == 111&&numn2 == 109 ){
        			b=0;
        		}else{
        			b=1;
        		}
        	}
        	
        	if(num ==95&&((num>=97&&num<=122)||(num>=65&&num<=90)||(num>=48&&num<=57))){
        		c=0;
        	}else{
        		c=1;
        	}
        	
        }
        if(a==1&&b==1&&c==1){
    		System.out.print("NO");
    	}else{
    		System.out.print("YES");
    	}
    }
}