Password Strength in Java

Java/Password_Strength/PasswordStrength.java

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+package password;
+
+import java.util.Scanner;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+public class PasswordStrength {
+
+	public static void main(String[] args) {
+		// TODO Auto-generated method stub
+        Scanner sc = new Scanner(System.in);
+        System.out.println("Enter the password:");
+        String password = sc.next();
+        check(password);
+	}
+
+	public static void check(String password) {
+		// TODO Auto-generated method stub
+		// ^ represents the starting of the string.
+		// (?=.*[a-z]) represent at least one lowercase character.
+		// (?=.*[A-Z]) represents at least one uppercase character.
+		// (?=.*\\d) represents at least one numeric value.
+		// (?=.*[-+_!@#$%^&*., ?]) represents at least one special character.
+		// . represents any character except line break.
+		// + represents one or more times.
+		String regex = "^(?=.*[a-z])(?=."+ "*[A-Z])(?=.*\\d)"+ "(?=.*[-+_!@#$%^&*., ?]).+$";
+
+		// Compile the ReGex
+        Pattern pattern = Pattern.compile(regex);
+
+        // if the string entered is null then the output will be password invalid
+        if (password == null) {
+            System.out.println("Password Invalid.");
+            return;
+        }
+
+        // Find match between given string & regular expression
+        Matcher matcher = pattern.matcher(password);
+
+        if (matcher.matches())
+            System.out.println("Password Valid and Strong.");
+        else
+            System.out.println("Weak Password.");
+    }
+
+	}

Java/Password_Strength/Readme.md

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+# Password Strength
+
+A program to check the strength of the password . For a strong password, the password must contain a mixture of upper case letters, a digit (including 0-9), and special characters with lower case letters.
+
+## Sample Input
+Sapna123@
+
+## Sample Output
+Password Valid and Strong.
+
+## Screenshot
+![demo](https://user-images.githubusercontent.com/56690856/98788220-90b3ed00-2426-11eb-94e6-c9115c61eebf.png)
+
+## Time Complexity
+O(N) 
+
+## Space Complexity
+O(1)