如何在 Java 中检查字符串是否为二进制

Question

   /**
     * Given a String as input, return true if the String represents a valid
     * binary value (i.e. contains only the digits 1 and 0). Returns false if
     * the String does not represent a binary value.
     *
     * @param value
     *            A String value that may contain a binary value
     * @return true if the String value contains a binary value, false otherwise
     */

No matter what I do it only returns false. I am new to programming and suck at seeing how the logic runs. Thank you for any and all help.

public static boolean validBinary(String value) {

    int b = Integer.parseInt(value);
    int binCount = 0;
    for(int i = 0; i < value.length(); i++) {
        int tempB = value.charAt(i);
        if(tempB % 10 == 0 || tempB % 10 == 1) {
            binCount = binCount + 1;
        }
        else {
            binCount = -1;
            break;
        }
    }
    if (binCount > 0) {
        return true;
    }
    else {
        return false;
    }

}

Answer 1

I believe your issue is here: int tempB = value.charAt(i); You convert tempB into a char, which is being cast to an int. But that converts it to its ASCII int value, so each '0' char is cast to 48 and each '1' value is cast to 49. Note: neither 48 nor 49 is zero or one mod 10, so nothing is ever being added to bin.

You need to convert each char to its actual integer value (namely, zero or one), with String.valueOf or Character.getNumericValue:

https://www.javatpoint.com/java-char-to-int

Otherwise (besides the fact that you never use the b variable anywhere, so don't really need it) your logic looks pretty sound.

Answer 2

Here is step by step analysis of your program.

public static boolean validBinary(String value) {

Get rid of the following as it is not used.

    int b = Integer.parseInt(value);

Initializing binCount and starting the loop.

    int binCount = 0;
    for(int i = 0; i < value.length(); i++) {
        int tempB = value.charAt(i);

This is where the problem starts. Even though tempB is declared an int it still has the value of an ASCII character. So '0' thru '9' are really 48 thru 57 inclusive. So instead of converting to integers, just compare them as they exist which are characters. In that case you can forget the % operator. So the new if statement should be:

    if (tempB == '0' || tempB == '1') {

instead of

    if(tempB % 10 == 0 || tempB % 10 == 1) {

Keep the rest of your code and the program should work just fine.

      binCount = binCount + 1;
    }
    else {
            binCount = -1;
            break;
        }
    }
    if (binCount > 0) {
        return true;
    }
    else {
        return false;
    }
}

Possible Improvements

The whole point of the exercise is to validate whether the number is binary. So you don't need any bookkeeping such as bincount do do that. As soon as your test for 0 or 1 fails, just return false . No need for further processing. But if you finish checking the entire string and haven't failed the test, then all the characters must be 0 or 1. So return true . That would look like this.

  for(int i = 0; i < value.length(); i++) {
        int tempB = value.charAt(i);
        if (tempB == '0' || tempB == '1') {
             continue; // process next character.
                       // continue skips rest of loop
         }
         return false;
   }
   // no failures, so
   return true;

Alternative logic without the continue could be:

  for(int i = 0; i < value.length(); i++) {
        int tempB = value.charAt(i);
        if (tempB != '0' && tempB != '1') {
             return false;
         }
   }
   // no failures, so
   return true;

Answer 3

You could use a basic regular expression:

public static final String BIT_REGEX = "[01]{1,}";
Pattern pattern = Pattern.compile(BIT_REGEX);
Matcher matcher = pattern.matcher(value);
isValid = matcher.matches();

Answer 4

public static boolean validBinary(String value) {

int binCount = 0;
int len = value.length();
for(int i = 0; i < len; i++) {
    char tempB = value.charAt(i);
    if(tempB == '0' || tempB == '1') {
        binCount = binCount + 1;
        continue;
    }
    else {
        binCount = -1;
        break;
    }
}
if (binCount > 0) {
    return true;
}
else {
    return false;
}

}