CODEWITHSUNDEEP
javareflectiondelegates
end-user
end-user

Reputation: 2947

how do I invoke a passed Method? This is delegation, right?

Ok, I know this is been asked and answered hundreds of times, and I know I'm probably going to get the "go search for the answer" response, but I'm going to try asking anyway. Very simply, I want to pass a method and use it to do the writing of a string. For example:

void writeStuff(Method method) {
    method.invoke("the string to write");
}

This way, I could hand it the method that would be receiving the string, such as System.out.print, or LOGGER.info. Heck, why not any method that accepts a String as an

Upvotes: 0

Views: 63

Answers (3)

Joop Eggen
Joop Eggen

Reputation: 109613

For a non-static method you need its object, otherwise this owner can be null. And then there are the exceptions to handle.

void writeStuff(Object owner, Method method) {
    method.invoke(owner, "the string to write");
}

Therefore till a next version of java, one uses an interface (with one method) and passes instances of these:

interface Printable { void print(String s); }

void writeStuff(Printable p) {
    p.print("...");
});

writeStuff(new Printable() {
    @Override public void print(String s) { System.out.println(s); }
});

For a static method, a function, one indeed needs no this (owner). In a top ultimate language like Algol68 (1968 but still active!) one could do:

REAL y = IF c THEN sin ELSE cos FI (x);

were sin and cos are names for code values having type PROC(REAL)REAL.

Java make a sad distinction between field and method: you can have a field int x and method void x(boolean) with the same name, overloaded methods boolean x(). For something like function objects one never could use System.out.println.

Upvotes: 1

tb-
tb-

Reputation: 1290

You have to specify the object on which the method should be called, too.

Indeed, you can read this from popular sources:

Javadoc API 1.7 for invoke

and

Sun/Oracle tutorial on invoking methods

--tb

Upvotes: 0

pedrosorio
pedrosorio

Reputation: 870

Did you read the documentation for invoke?

http://docs.oracle.com/javase/1.4.2/docs/api/java/lang/reflect/Method.html#invoke(java.lang.Object, java.lang.Object[])

Upvotes: 0

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