Is there a way to pass a method as a parameter to a method?

Question

I'm writing a program and I want to know if I can pass a method as a parameter of another method. For example, something of the following:

public boolean update(Method m){ //input is a method
    int i = m.execute();
    // logic relating to the value of i
}

I want to know if I can do this in java. I'm currently reading about functional programming and Reflection right now.

Are you able to use Java 8? It adds support for lambda expressions, which makes functional programming a lot easier. If not, then reflection is the way to do what you're asking. — Andrew Williamson, Apr 24 '16 at 01:07
I gather from your question that you haven't tried to create a simple program to try it out? Even if it doesn't work, it makes for a better question when you write code, test it, and tell us about the result. See http://stackoverflow.com/help/mcve — Hank D, Apr 24 '16 at 01:10
Yes. Lambdas are very useful and offer some functional programming capabilities in Java — Logan, Apr 24 '16 at 01:10
See this https://stackoverflow.com/questions/4685563/how-to-pass-a-function-as-a-parameter-in-java — sebenalern, Apr 24 '16 at 01:11

Hank D · Accepted Answer · 2016-04-24T01:35:38.190

This has nothing to do with reflection, but you can pass "method references" if you are using java 8+. Assuming from your example that you intend to use methods that take no parameters and just return an int, you could do this:

public class MyClass {
    public int getIntMemberFunction(){ ... }
    public static int getIntStaticFunction(){ ... }
}

with your update function modified to look like this,

public boolean update(IntSupplier s){ //input is a method reference or lambda
    int i = s.get();
    // logic relating to the value of i
}

Then you could call update passing in a reference to any static function on any class as long as it takes no parameters and returns an int, like this:

boolean result = update(MyClass::getIntStaticFunction);

or you could call update passing in a reference to any member function of a specific object as long as it takes no parameters and returns an int, like this:

MyClass myClassInstance = ...
boolean result = update(myClassInstance::getIntMemberFunction);

If you want to add methods that take 1 or 2 parameters, you could create versions of update that take ToIntFunction or ToIntBiFunction. Beyond 2 parameters you would have to add your own functional interfaces.

score 0 · Answer 2 · answered Apr 24 '16 at 01:12

One way to do it is to use Interfaces. In Java you can pass as argument to a function an object that implements a particular interface and thus you can call that method on that object. More modern languages, such as Python, Swift, Javascript, have better support for this idiom.

Is there a way to pass a method as a parameter to a method?

2 Answers2