java optional parameters

1void foo(String a, Integer b) {
2    //...
3}
4
5void foo(String a) {
6    foo(a, 0); // here, 0 is a default value for b
7}
8
9foo("a", 2);
10foo("a");

1void foo(String a, Optional<Integer> bOpt) {
2    Integer b = bOpt.isPresent() ? bOpt.get() : 0;
3    //...
4}
5
6foo("a", Optional.of(2));
7foo("a", Optional.<Integer>absent());

1void foo(String a, Integer... b) {
2    Integer b1 = b.length > 0 ? b[0] : 0;
3    Integer b2 = b.length > 1 ? b[1] : 0;
4    //...
5}
6
7foo("a");
8foo("a", 1, 2);

1//Java 9 and above only    
2@SuppressWarnings("unchecked")
3    static <T> T getParm(Map<String, Object> map, String key, T defaultValue)
4    {
5        return (map.containsKey(key)) ? (T) map.get(key) : defaultValue;
6    }
7
8    void foo(Map<String, Object> parameters) {
9        String a = getParm(parameters, "a", "");
10        int b = getParm(parameters, "b", 0);
11        // d = ...
12    }
13
14    foo(Map.of("a","a",  "b",2,  "d","value"));

1@SuppressWarnings("unchecked")
2static <T> T getParm(Map<String, Object> map, String key, T defaultValue) {
3  return (map.containsKey(key)) ? (T) map.get(key) : defaultValue;
4}
5
6void foo(Map<String, Object> parameters) {
7  String a = getParm(parameters, "a", "");
8  int b = getParm(parameters, "b", 0);
9  // d = ...
10}
11
12foo(Map.of("a","a",  "b",2,  "d","value"));
13

1    void foo(String a, Object... b) {
2        Integer b1 = 0;
3        String b2 = "";
4        if (b.length > 0) {
5          if (!(b[0] instanceof Integer)) { 
6              throw new IllegalArgumentException("...");
7          }
8          b1 = (Integer)b[0];
9        }
10        if (b.length > 1) {
11            if (!(b[1] instanceof String)) { 
12                throw new IllegalArgumentException("...");
13            }
14            b2 = (String)b[1];
15            //...
16        }
17        //...
18    }
19
20    foo("a");
21    foo("a", 1);
22    foo("a", 1, "b2");
23