Can someone explain lambdas?
Java for AWS Lambda
What is the breakdown for Java's lambda syntax? - Stack Overflow
Any tips for understanding and practicing Java lambda expressions?
So I’m reading a book on Java, and it’s talking about lambdas. The syntax seems simple enough, but the author hasn’t described why you would use them over a regular function. They’re being used in the context of functions that don’t have bodies (abstracts, I think?), but I don’t understand why I would use those either.
Hi,
What is the best way to run lambda functions using Java, I have read numerous posts on reddit and other blogs and now I am more confused what would be a better choice?
Our main use case is to parse files from S3 and insert data into RDS MySQL database.
If we use Java without any framework, we dont get benefits of JPA, if we use Spring Boot+JPA then application would perform poorly? Is Quarkus/Micronaut with GraalVM a better choice(I have never used Quarkus/Micronaut/GraalVM, does GraalVM require paid license to be used in production?), or can Quarkus/Micronaut be used without GraalVM, and how would be the performance?
Syntax is:
arguments -> body
where arguments can be either
()a single variable if the type of that variable can be inferred from the context
a sequence of variables, with or without types (or since Java 11, with
var), in parentheses.
Examples:(x),(x, y),(int x, int y),(var x, var y)(Java 11+).
The following are invalid:(int x, y),(x, var y),(var x, int y)
and body can be either an expression or a {...} block with statements. The expression (other than a method or constructor call) is simply returned, i.e. () -> 2 is equivalent to () -> {return 2;}
In case of lambda expressions like () -> f() (the body is a method or constructor call expression):
if
f()returnsvoid, they are equivalent to() -> { f(); }otherwise, they are equivalent to either
() -> { f(); }or() -> { return f(); }). The compiler infers it from the calling context, but usually it will prefer the latter.
Therefore, if you have two methods: void handle(Supplier<T>) and void handle(Runnable), then:
handle(() -> { return f(); })andhandle(() -> x)will call the first one,handle(() -> { f(); }will call the second one, andhandle(() -> f()):if
f()returnsvoidor a type that is not convertible toT, then it will call the second oneif
f()returns a type that is convertible toT, then it will call the first one
The compiler tries to match the type of the lambda to the context. I don't know the exact rules, but the answer to:
What would happen if there were two SwingUtilities.invokeLater methods which differ only in parameter list?
is: it depends on what would be those parameter lists. If the other invokeLater had also exactly one parameter and that parameter would be of type that is also an interface with one method of type void*(), well, then it would complain that it cannot figure out which method you mean.
Why are they written as they are? Well, I think it's because syntax in C# and Scala is almost the same (they use => rather than ->).
The syntax is
(parameter_list_here) -> { stuff_to_do; }
The curly braces can be omitted if it's a single expression. The regular parentheses around the parameter list can be omitted if it's a single parameter.
The syntax only works for all functional interfaces. The @FunctionalInterface annotation tells the compiler that you intend to write such an interface and gives a compile error if you do not meet the requirement(s) - for example it must only have 1 overrideable method.
@FunctionalInterface
interface TestInterface {
void dostuff();
}
Runnable is also declared like that. Other interfaces are not, and they cannot be used with lambda functions.
Now that we've made a new functional interface with a method that takes no parameters, how about we test the question you had about "collision" in the signatures?
public class Main {
private void test(Runnable r) {
}
private void test(TestInterface ti) {
}
public static void main(String[] args) {
test(() -> { System.out.println("test");})
}
@FunctionalInterface
interface TestInterface {
void dostuff();
}
}
Result: compile error: ambigouous call to method test.
You see, the compiler/VM(if done runtime) finds the appropriate methods and their parameter list and sees if the parameter is a functional interface and if it is it creates an anonymous implementation of that interface. Technically (in byte code) it's different from an anonymous class, but otherwise identical (you won't see Main$1.class files).
Your example code (courtesy of Netbeans) can also be replaced with
SwingUtilities.invokeLater(MainAppJFrame::new);
Btw. :)
Hey guys, I need some help with Java lambda expressions. I kind of get how they work, but I don’t really know how to practice or get better at using them. How did you all learn and get comfortable with lambdas? Any advice or recommendations?