判断一个字符串字符是否唯一

package lishi;

import java.util.Scanner;

public class the_only_Z {

public static void main(String[] args) {
// TODO Auto-generated method stub
Scanner sc = new Scanner(System.in);
String str = sc.next();
if(ifUniqueChars(str)){
System.out.println("This is a only character.");
}else{
System.out.println("This isn't a only character.");
}

}

public static boolean ifUniqueChars(String str){
int checker = 0;
for(int i = 0;i<str.length();i++){
int val = str.charAt(i)-'a';
if((checker&(1<<val))>0)return false;
checker|=(1<<val);
}
return true;
}

}