Equivalent for Python's lambda functions in Java?

Question

Can someone please tell me if there is an equivalent for Python\'s lambda functions in Java?

Answer 1

As already pointed out, lambda expressions were introduced in Java 8.

If you're coming from python, C# or C++, see the excellent example by Adrian D. Finlay, which I personally found much easier to understand than the official documentation.

Here's a quick peek based on Adrian's example, created using a jupyter notebook with the python kernel and IJava java kernel.

Python:

# lambda functions
add = lambda x, y : x + y
multiply = lambda x, y : x * y
# normal function. In python, this is also an object.
def add_and_print_inputs(x, y):
    print("add_and_print inputs : {} {}".format(x,y))
    return x + y
print(add(3,5), multiply(3,5), add_and_print_inputs(3,5))

Output:

add_and_print inputs : 3 5
8 15 8

Java lambda functions can be multiline, whereas in python they are a single statement. However there is no advantage here. In python, regular functions are also objects. They can be added as parameters to any other function.

# function that takes a normal or lambda function (myfunc) as a parameter
def double_result(x,y,myfunc):
    return myfunc(x,y) * 2
double_result(3,5,add_and_print_inputs)

Output:

add_and_print inputs : 3 5
16

Java:

// functional interface with one method
interface MathOp{
    int binaryMathOp(int x, int y);
}
// lambda functions
MathOp add = (int x, int y) -> x + y;
MathOp multiply = (int x, int y) -> x * y;
// multiline lambda function
MathOp add_and_print_inputs = (int x, int y) -> {
    System.out.println("inputs : " + x + " " + y);
    return x + y;};// <- don't forget the semicolon
// usage
System.out.print("" +
add.binaryMathOp(3,5) + " " +
multiply.binaryMathOp(3,5) + " " + 
add_and_print_inputs.binaryMathOp(3,5))

Output:

inputs : 3 5
8 15 8

And when used as a parameter:

// function that takes a function as a parameter
int doubleResult(int x, int y, MathOp myfunc){
    return myfunc.binaryMathOp(x,y) * 2;
}
doubleResult(3,5,add_and_print_inputs)

Output:

inputs : 3 5
16