计算随意无序字符串中的最大有序串

private void compare() {
//定义个无序字符串
String str = "sdifsdafsdabfwqicweedio";
//置于hashset去重
HashSet<Character> set = new HashSet<Character>();
for (int i = 0; i < str.length(); i++) {
set.add(str.charAt(i));
}
System.out.println("set=" + set);
Object[] list = set.toArray();
Object temp = "";
//冒泡排序
for (int i = 0; i < list.length; i++) {
for (int j = i; j < list.length; j++) {
char ch = (Character) list[i];
char ca = (Character) list[j];
if (ch > ca) {
temp = list[i];
list[i] = list[j];
list[j] = temp;
}
}
}
//此for为了方便展示排序后的数组的结果
String result = "";
for (int i = 0; i < list.length; i++) {
result += "" + list[i];
}
System.out.println("有序串=" + result);
}