生成随机数的类

public String getString(){
String str = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
Random ran = new Random();
StringBuffer sb = new StringBuffer();

for (int i = 0; i <10; i++) {
char ch = str.charAt(ran.nextInt(str.length()));
sb.append(ch);
}
return sb.toString();
}

//随机生成一个字符串，长度由传进来的值定义
public String getString(int len){
String str = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
Random ran = new Random();
StringBuffer sb = new StringBuffer();

for (int i = 0; i <len; i++) {
char ch = str.charAt(ran.nextInt(str.length()));
sb.append(ch);
}
return sb.toString();
}
//随机生成字符串，返回List集合中
public List<String> getStringList(int len){
List<String> list = new ArrayList<String>();

for (int i = 0; i < len; i++) {
String str = getString();
list.add(str);
}

return list;
}