### Question:
AlphaNumericGenerator { public AlphaNumericGenerator(int length, String symbols){ if (length < 1) throw new IllegalArgumentException(); if (symbols.length() < 2) throw new IllegalArgumentException(); this.random = new SecureRandom(); this.symbols = symbols.toCharArray(); this.buf = new char[length]; } AlphaNumericGenerator(int length, String symbols);  AlphaNumericGenerator(int length);  AlphaNumericGenerator(String format); String generate(); static final String upper; static final String lower; static final String digits; static final String alphanum; public String format; }### Answer:
@Test public void testAlphaNumericGenerator(){ AlphaNumericGenerator alphaNumericGenerator = new AlphaNumericGenerator(15); Assert.assertNotNull(alphaNumericGenerator.generate()); alphaNumericGenerator = new AlphaNumericGenerator("DD??"); Assert.assertNotNull(alphaNumericGenerator.generate()); }