Merge pull request #203 from ThexXTURBOXx/regex

Implement RegEx Date Validation

Author: SarthakKeshari

String Handling/DateValidation.java

@@ -0,0 +1,56 @@
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.util.regex.Pattern;
+
+/**
+ * Parse a given date in dd/yyyy/mm format with different difficulties
+ */
+public class DateValidation {
+
+    /**
+     * Very naive approach.
+     */
+    public static Pattern EASY_FORMAT = Pattern.compile("\\d\\d/\\d\\d\\d\\d/\\d\\d");
+
+    /**
+     * Let's split up into different cases, i.e. different months.
+     */
+    public static Pattern MEDIUM_FORMAT = Pattern.compile(""
+            + "(((0[1-9])|([1-2][0-9]))/\\d\\d\\d\\d/02" // February
+            + "|((0[1-9])|([1-2][0-9])|(3[0-1]))/\\d\\d\\d\\d/(01|03|05|07|08|10|12)" // Months with 31 days
+            + "|((0[1-9])|([1-2][0-9])|(30))/\\d\\d\\d\\d/(04|06|09|11))" // Months with 30 days
+    );
+
+    /**
+     * For the hard format, take into account that a year is a leap year if it is divisible by 4, but not by 100.
+     * However, if the year is divisible by 400, it will nevertheless be counted as a leap year.
+     */
+    public static Pattern HARD_FORMAT = Pattern.compile(""
+            + "(29/" // 29th day
+            + "((([0-9]{2})(04|08|[2468][048]|[13579][26]))|" // First two numbers are arbitrary; if the last two
+                                                              // numbers are divisible by 4, but are not 00
+                                                              // So, the year is divisible by 4, but not 100
+            + "(00|04|08|[2468][048]|[13579][26])00)" // If the first two numbers are divisible by 4 and the last two
+                                                      // are 00. So, the year is divisible by 400
+            + "/02" // February
+            + "|((0[1-9])|(1[0-9])|(2[0-8]))/\\d\\d\\d\\d/02" // "Normal" Februaries
+            + "|((0[1-9])|([1-2][0-9])|(3[0-1]))/\\d\\d\\d\\d/(01|03|05|07|08|10|12)" // Months with 31 days
+            + "|((0[1-9])|([1-2][0-9])|(30))/\\d\\d\\d\\d/(04|06|09|11))" // Months with 30 days
+    );
+
+    public static void main(String[] args) throws IOException {
+        System.out.println("Starting the Regex Date Validation...");
+
+        try (InputStreamReader isr = new InputStreamReader(System.in);
+             BufferedReader in = new BufferedReader(isr)) {
+            System.out.print("Enter date to validate: ");
+            String date = in.readLine();
+
+            System.out.println("Matches dd/yyyy/mm format:   " + EASY_FORMAT.matcher(date).matches());
+            System.out.println("Matches also days per month: " + MEDIUM_FORMAT.matcher(date).matches());
+            System.out.println("Matches also leap years:     " + HARD_FORMAT.matcher(date).matches());
+        }
+    }
+
+}