refactor: PasswordGen

Author: alxkm

src/main/java/com/thealgorithms/others/PasswordGen.java

@@ -12,21 +12,32 @@
  * @date 2017.10.25
  */
 final class PasswordGen {
+    private static final String UPPERCASE_LETTERS = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
+    private static final String LOWERCASE_LETTERS = "abcdefghijklmnopqrstuvwxyz";
+    private static final String DIGITS = "0123456789";
+    private static final String SPECIAL_CHARACTERS = "!@#$%^&*(){}?";
+    private static final String ALL_CHARACTERS = UPPERCASE_LETTERS + LOWERCASE_LETTERS + DIGITS + SPECIAL_CHARACTERS;
+
     private PasswordGen() {
     }
 
-    static String generatePassword(int minLength, int maxLength) {
-        Random random = new Random();
-
-        String upper = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
-        String lower = "abcdefghijklmnopqrstuvwxyz";
-        String numbers = "0123456789";
-        String specialChars = "!@#$%^&*(){}?";
+    /**
+     * Generates a random password with a length between minLength and maxLength.
+     *
+     * @param minLength The minimum length of the password.
+     * @param maxLength The maximum length of the password.
+     * @return A randomly generated password.
+     * @throws IllegalArgumentException if minLength is greater than maxLength or if either is non-positive.
+     */
+    public static String generatePassword(int minLength, int maxLength) {
+        if (minLength > maxLength || minLength <= 0 || maxLength <= 0) {
+            throw new IllegalArgumentException("Incorrect length parameters: minLength must be <= maxLength and both must be > 0");
+        }
 
-        String allChars = upper + lower + numbers + specialChars;
+        Random random = new Random();
 
-        List<Character> letters = new ArrayList<Character>();
-        for (char c : allChars.toCharArray()) {
+        List<Character> letters = new ArrayList<>();
+        for (char c : ALL_CHARACTERS.toCharArray()) {
             letters.add(c);
         }
 
@@ -36,7 +47,7 @@ static String generatePassword(int minLength, int maxLength) {
 
         // Note that size of the password is also random
         for (int i = random.nextInt(maxLength - minLength) + minLength; i > 0; --i) {
-            password.append(letters.get(random.nextInt(letters.size())));
+            password.append(ALL_CHARACTERS.charAt(random.nextInt(ALL_CHARACTERS.length())));
         }
 
         return password.toString();

src/test/java/com/thealgorithms/others/PasswordGenTest.java

@@ -1,5 +1,6 @@
 package com.thealgorithms.others;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
@@ -10,7 +11,7 @@ public class PasswordGenTest {
     @Test
     public void failGenerationWithSameMinMaxLengthTest() {
         int length = 10;
-        assertThrows(IllegalArgumentException.class, () -> { PasswordGen.generatePassword(length, length); });
+        assertThrows(IllegalArgumentException.class, () -> PasswordGen.generatePassword(length, length));
     }
 
     @Test
@@ -23,12 +24,30 @@ public void generateOneCharacterPassword() {
     public void failGenerationWithMinLengthSmallerThanMaxLengthTest() {
         int minLength = 10;
         int maxLength = 5;
-        assertThrows(IllegalArgumentException.class, () -> { PasswordGen.generatePassword(minLength, maxLength); });
+        assertThrows(IllegalArgumentException.class, () -> PasswordGen.generatePassword(minLength, maxLength));
     }
 
     @Test
     public void generatePasswordNonEmptyTest() {
         String tempPassword = PasswordGen.generatePassword(8, 16);
         assertTrue(tempPassword.length() != 0);
     }
+
+    @Test
+    public void testGeneratePasswordWithMinGreaterThanMax() {
+        Exception exception = assertThrows(IllegalArgumentException.class, () -> PasswordGen.generatePassword(12, 8));
+        assertEquals("Incorrect length parameters: minLength must be <= maxLength and both must be > 0", exception.getMessage());
+    }
+
+    @Test
+    public void testGeneratePasswordWithNegativeLength() {
+        Exception exception = assertThrows(IllegalArgumentException.class, () -> PasswordGen.generatePassword(-5, 10));
+        assertEquals("Incorrect length parameters: minLength must be <= maxLength and both must be > 0", exception.getMessage());
+    }
+
+    @Test
+    public void testGeneratePasswordWithZeroLength() {
+        Exception exception = assertThrows(IllegalArgumentException.class, () -> PasswordGen.generatePassword(0, 0));
+        assertEquals("Incorrect length parameters: minLength must be <= maxLength and both must be > 0", exception.getMessage());
+    }
 }