Is lambda expression and functional pointers different or same? How?

[jagrutkumar dalwadi]

I am not sure that lambda expression and function pointers are same or different. can anyone please help me in this?

[Campbell Ritchie]

Very different.
Does Java8 even support function pointers?

[Jesper de Jong]

Java 8 will not have function pointers.

There is a notation, however, to refer to methods by their name (method references). It uses the "::" notation. The following pieces of code are equivalent:

List<String> names = ...;

// Print all names; reads as "for each name in names, do System.out.println(name)"
names.forEach(name -> System.out.println(name));

// Print all names; reads as "for each name in names, call the method System.out.println"
names.forEach(System.out::println);

You can assign method references to functional interfaces (interfaces with a single abstract method):

// c refers to the System.out.println() method
Consumer<String> c = System.out::println;

So, it looks a little bit like a function pointer in languages such as C or C++.

[Cay Horstmann]

As Jesper says, the equivalent of a function pointer in C/C++ is the method reference in Java.

For example,

Arrays.sort(strings, String::compareToIgnoreCase)

does what you think it does. But lambda expressions are more powerful. Look at Kernighan & Ritchie's example for function pointers:

qsort((void**) lineptr, 0, nlines-1, (int (*)(void*,void*))(numeric ? numcmp : strcmp));

Here, strcmp is the equivalent of String::compare. And numcmp is a function that they wrote elsewhere. But in C, you must write it as a separate function. With lambda expressions, you can write

(s, t) -> Integer.compare(Integer.parseInt(s), Integer.parseInt(t))

and then just pass it to Arrays.sort.

Cheers,

Cay