在JAVA中如何检查两个ArrayList中的多个数字

Question

Trying to check if a number is binary or not - so User will type an integer & will validate if that is binary or not. My code is as below & it is always returning False so the if statement is not working - also tried to convert to string but getting the same result - Thanks

public static void main(String[] args) {

int aa = 5101012;

ArrayList dd = new ArrayList();

while(aa>0){
    dd.add(aa%10);
    aa = aa/10;}

ArrayList dd1 = new ArrayList();

dd1.add(2);
dd1.add(3);
dd1.add(4);
dd1.add(5);
dd1.add(6);
dd1.add(7);
dd1.add(8);
dd1.add(9);

System.out.println(dd1.contains(dd));}}

Answer 1

***************************REGEX SHORT VERSION********************************************************* If you want to shorten your code you could use regex:

public static void main(String[] args) {

    int aa = 10101;
    String test = "" + aa;
    System.out.println("" + !test.matches(".*[23456789].*"));

}

This will return true for 10101 and false for 5101012 .

************************************LONG VERSION********************************************************* You should check each element individually if you want to see which digits are binary and which ones aren't:

public static void main(String[] args) {

    int aa = 5101012;

    ArrayList<Integer> dd = new ArrayList<Integer>();

    while(aa>0){
        dd.add(aa%10);
        aa = aa/10;}

    ArrayList<Integer> dd1 = new ArrayList<Integer>();

    dd1.add(2);
    dd1.add(3);
    dd1.add(4);
    dd1.add(5);
    dd1.add(6);
    dd1.add(7);
    dd1.add(8);
    dd1.add(9);

    for(Integer a : dd)
    {
        System.out.println(dd1.contains(a));
    }
}

You were trying to see if dd1 contains an arraylist of objects which it doesn't it contains objects( Integer ) individually.

Answer 2

One way (not the most elegant) is to convert it to string and then do:

    for (int i = 0; i < string.length(); i++) {
if ( string.charAt(i) != '1' && string.charAt(i) != '0') {
System.out.println("Not a binary number!");
break;
}
}