Java Coding Problems

4. Checking whether a string contains only digits

The solution to this problem relies on the Character.isDigit() or String.matches() method.

The solution relying on Character.isDigit() is pretty simple and fast—loop the string characters and break the loop if this method returns false:

public static boolean containsOnlyDigits(String str) {  for (int i = 0; i < str.length(); i++) {    if (!Character.isDigit(str.charAt(i))) {      return false;    }  }  return true;}

In Java 8 functional style, the preceding code can be rewritten using anyMatch():

public static boolean containsOnlyDigits(String str) {  return !str.chars()    .anyMatch(n -> !Character.isDigit(n));}

Another solution relies on String.matches(). This method returns a boolean value indicating whether ...