Optional parameter in java (can be null)

Question

I have a function with a boolean parameter, but it could be null too.

If it's true or false, it makes a query with a "WHERE" clause. If it was null, the query has no "WHERE" clause, only the select clause.

How can I do that in Java ?

Answer 1

Use Boolean class

public String foo(Boolean addWhere){
    String query = "SELECT * FROM tbl";
    if(addWhere != null){
        query += (addWhere? " WHERE true" : " WHERE false");
    }
    return query;
}

Call it as following,

String q = foo(false);

Answer 2

You can use java.lang.Boolean; this is the wrapper class for primitive boolean. The value can be null, Boolean.TRUE or Boolean.FALSE, but due to auto-unboxing you can also directly compare with true and false.

Answer 3

There are several ways to do so:

• Declaring two functions, one with a boolean parameter and one without a parameter.
• Declaring one function with an Optional<Boolean> parameter.
• Declaring one funktion with a Boolean parameter, where null is the unspecified case.