/*******************************************************************************
* Copyright (c) 2013-2015 IBM Corp.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
*    http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*******************************************************************************/

package com.acmeair.service;

import java.util.Random;

public class KeyGenerator {

  public Object generate() {
    char[] chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ".toCharArray();
    StringBuilder sb = new StringBuilder();
    Random random = new Random();
    for (int i = 0; i < 6; i++) {
        char c = chars[random.nextInt(chars.length)];
        sb.append(c);
    }
    return "booking number " + sb.toString();
  }
}

/*******************************************************************************
* Copyright (c) 2013-2015 IBM Corp.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
*    http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*******************************************************************************/

package com.acmeair.service;

import java.util.Random;

public class KeyGenerator {

  public Object generate() {
    char[] chars = "1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ".toCharArray();
    StringBuilder sb = new StringBuilder();
    Random random = new Random();
    for (int i = 0; i < 6; i++) {
        char c = chars[random.nextInt(chars.length)];
        sb.append(c);
    }
    return "Booking number " + sb.toString();
  }
}

Update KeyGenerator.java