private String octal;

private int decimal;

public Octal(String octal) {

this.octal = octal;

this.decimal = getDecimalFromOctal(octal);

}

public int getDecimal() {

return decimal;

}

private static int getDecimalFromOctal(String octal) {

if (!isValid(octal)) {

return 0;

}

int sum = 0;

for (int index = 0; index < octal.length(); index++) {

sum += Character.getNumericValue(octal.charAt(index)) * Math.pow(8, octal.length() - index - 1);

}

return sum;

}

private static boolean isValid(String binaryRepresentation) {

return binaryRepresentation.chars()

.allMatch(x -> Character.isDigit((char) x) && Character.getNumericValue((char) x) < 8);

}