Java optional parameters

Question

How do I use optional parameters in Java? What specification supports optional parameters?

Answer 1

There is optional parameters with Java 5.0. Just declare your function like this:

public void doSomething(boolean... optionalFlag) {
    //default to "false"
    //boolean flag = (optionalFlag.length >= 1) ? optionalFlag[0] : false;
}

you could call with doSomething(); or doSomething(true); now.

Answer 2

Java now supports optionals in 1.8, I'm stuck with programming on android so I'm using nulls until I can refactor the code to use optional types.

Object canBeNull() {
    if (blah) {
        return new Object();
    } else {
        return null;
    }
}

Object optionalObject = canBeNull();
if (optionalObject != null) {
    // new object returned
} else {
    // no new object returned
}

Answer 3

There are no optional parameters in Java. What you can do is overloading the functions and then passing default values.

void SomeMethod(int age, String name) {
    //
}

// Overload
void SomeMethod(int age) {
    SomeMethod(age, "John Doe");
}

Answer 4

We can make optional parameter by Method overloading or Using DataType...

|*| Method overloading :

RetDataType NameFnc(int NamePsgVar)
{
    // |* Code Todo *|
    return RetVar;
}

RetDataType NameFnc(String NamePsgVar)
{
    // |* Code Todo *|
    return RetVar;
}

RetDataType NameFnc(int NamePsgVar1, String NamePsgVar2)
{
    // |* Code Todo *|
    return RetVar;
}

---

Easiest way is

|*| DataType... can be optional parameter

RetDataType NameFnc(int NamePsgVar, String... stringOpnPsgVar)
{
    if(stringOpnPsgVar.length == 0)  stringOpnPsgVar = DefaultValue; 

    // |* Code Todo *|
    return RetVar;
}

---

Answer 5

If it's an API endpoint, an elegant way is to use "Spring" annotations:

@GetMapping("/api/foos")
@ResponseBody
public String getFoos(@RequestParam(required = false, defaultValue = "hello") String id) { 
    return innerFunc(id);
}

Notice in this case that the innerFunc will require the variable, and since it's not api endpoint, can't use this Spring annotation to make it optional. Reference: https://www.baeldung.com/spring-request-param

Answer 6

varargs could do that (in a way). Other than that, all variables in the declaration of the method must be supplied. If you want a variable to be optional, you can overload the method using a signature which doesn't require the parameter.

private boolean defaultOptionalFlagValue = true;

public void doSomething(boolean optionalFlag) {
    ...
}

public void doSomething() {
    doSomething(defaultOptionalFlagValue);
}