StringBuffer sb = new StringBuffer();
for(int i='a';i<='z'; i++){
sb.append((char) i);
}
for(int i='A';i<='Z'; i++){
sb.append((char) i);
}
java.util.Random random = new java.util.Random();
int randomIndex = random.nextInt(sb.length());
char s = sb.charAt(randomIndex);
System.out.println("原始字符串: " + sb);
System.out.println("隨機下標: " + randomIndex);
System.out.println("隨機字符: " + s);
}
自己再封裝壹下即可