Adding Password Generator in Java (#63)

Java/Random Password Generator Java/README.md

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+This is a password generator program that allows you to generate passwords as well as mention length of each password.
+
+Here is a screenshot of the welcome screen of the application.
+

Java/Random Password Generator Java/src/App.java

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+/* 
+* This program generates a password of specified length
+*/
+
+import java.util.Random;
+class App {
+
+    // All the capital letters
+    static final char ALPHA_CAPS[] = { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K',
+            'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V',
+            'W', 'X', 'Y', 'Z'
+    };
+
+    // All the small letters
+    static final char ALPHA_LOWER[] = { 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k',
+            'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
+            'w', 'x', 'y', 'z'
+    };
+
+    //All the numeric characters
+    static final char NUMERIC[] = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9'};
+
+    //All the special characters
+    static final char SPECIAL[] = { '!', '@', '#', '$', '%', '^', '&', '*', '|', ';', ':' };
+
+    // All characters
+    static final char ALL_CHARS[] = { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K',
+            'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V',
+            'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k',
+            'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
+            'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
+            '!', '@', '#', '$', '%', '^', '&', '*', '|', ';', ':'
+    };
+
+    public static void main(String[] args) {
+        System.out.println("Random password generator in Java");
+        System.out.println(generatePassword(8));
+        System.out.println(generatePassword(14));
+        System.out.println(generatePassword(3));
+        System.out.println(generatePassword(10));
+        System.out.println(generatePassword(9));
+
+    }
+
+    /* 
+     * Password generating function
+     * Input: Password length
+     * Output: Password string
+     */
+
+    private static String generatePassword(int length) {
+        // Assert that given length is that greater than 3
+        if (length < 4) {
+            System.out.print("Length of Password to generate must be greater than 3");
+            return "";
+        }
+
+        char password[] = new char[length];
+
+        // Random number generator
+        Random random = new Random();
+
+        // Generate at least one character of each type
+        password[0] = ALPHA_CAPS[random.nextInt(ALPHA_CAPS.length)];
+        password[1] = ALPHA_LOWER[random.nextInt(ALPHA_LOWER.length)];
+        password[2] = NUMERIC[random.nextInt(NUMERIC.length)];
+        password[3] = SPECIAL[random.nextInt(SPECIAL.length)];
+
+        // Generate remaining number of characters
+        for (int i = 4; i < length; i++) {
+            password[i] = ALL_CHARS[random.nextInt(ALL_CHARS.length)];
+        }
+
+        // Shuffling all the characters
+        for (int i = 0; i < password.length; i++) {
+            int r = random.nextInt(password.length);
+            char temp = password[r];
+            password[r] = password[i];
+            password[i] = temp;
+        }
+
+        // Create the string from password arr
+        return new String(password);
+
+    }
+}