generate a random string in java

/**
 * @author lautturi.com
 * Java example: Randomly generate a string of the specified length injava
 */

import java.util.*;

public class Lautturi {

	static String randomString(int len)
    {
  
        // LowerCase Letters
		int a=97;
		int z=122;
		// UpperCase Letters
		int A=65;
		int Z=90;
		// Digits
		int d0 = 48;
		int d9=57;
  
        Random random = new Random();
  
        StringBuffer sb = new StringBuffer(len);
  
        for (int i = 0; i < len; i++) {
  
        	int randtype = (int)(random.nextFloat()*3);
        	int nextRandomChar = 0;
        	
        	switch(randtype) {
        		case 0:
        			nextRandomChar = a + (int)(random.nextFloat() * (z - a + 1));
        		break;
        		case 1:
        			nextRandomChar = A + (int)(random.nextFloat() * (Z - A + 1));
        		break;
        		case 2:
        			nextRandomChar = d0 + (int)(random.nextFloat() * (d9 - d0 + 1));
        		break;
        		default:
        			nextRandomChar = a + (int)(random.nextFloat() * (z - a + 1));
        		break;
        	}
        	sb.append((char)nextRandomChar);
        }
 
        return sb.toString();
    }
	
	public static void main(String[] args) {

		String rndStr = randomString(10);
		
		System.out.println(rndStr);
        
	}

}

output example:

7xqJtJNY6Z