public class Main {
public static boolean containsOnlyNumbers(String str) {
for (int i = 0; i < str.length(); i++) {
if (!Character.isDigit(str.charAt(i)))
return false;
}
return true;
}
public static void main(String[] args) {
System.out.println(containsOnlyNumbers("123456"));
System.out.println(containsOnlyNumbers("123abc456"));
}
}
/*
true
false
*/