how to use optional array parameter ... in java code example

Example 1: java how to make a parameter optional

//Java 9 and above only    
@SuppressWarnings("unchecked")
    static <T> T getParm(Map<String, Object> map, String key, T defaultValue)
    {
        return (map.containsKey(key)) ? (T) map.get(key) : defaultValue;
    }

    void foo(Map<String, Object> parameters) {
        String a = getParm(parameters, "a", "");
        int b = getParm(parameters, "b", 0);
        // d = ...
    }

    foo(Map.of("a","a",  "b",2,  "d","value"));

Example 2: java how to make a parameter optional

void foo(String a, Object... b) {
    Integer b1 = 0;
    String b2 = "";
    if (b.length > 0) {
      if (!(b[0] instanceof Integer)) { 
          throw new IllegalArgumentException("...");
      }
      b1 = (Integer)b[0];
    }
    if (b.length > 1) {
        if (!(b[1] instanceof String)) { 
            throw new IllegalArgumentException("...");
        }
        b2 = (String)b[1];
        //...
    }
    //...
}

foo("a");
foo("a", 1);
foo("a", 1, "b2");