java按长度生成随机数字和字母组合

import java.util.Random;

public static Random random = new Random();

public static String getRandom(int length){
	StringBuilder ret= new StringBuilder();   
	    for(int i = 0; i < length; i++) {   
	        boolean isChar = (random.nextInt(2) % 2 == 0) ;// 输出字母还是数字   
	        if(isChar) { // 字符串    
	            int choice = random.nextInt(2) % 2 == 0 ? 65 : 97; //取得大写字母还是小写字母   
	            ret.append((char) (choice + random.nextInt(26)));   
	        } else { // 数字   
	            ret.append(Integer.toString(random.nextInt(10)));   
	        }
	    }
	    return ret.toString();   
}