The problem with this question is that it's not clear whether you see the purpose of a Function, which has a method apply(T t).
The value of all the functional types is that you can pass code around like data. One common use of this is the callback, and until Java 8, we used to have to do this with anonymous class declarations:
ui.onClick(new ClickHandler() {
public void handleAction(Action action) {
// do something in response to a click, using `action`.
}
}
Now with lambdas we can do that much more tersely:
ui.onClick( action -> { /* do something with action */ });
We can also assign them to variables:
Consumer clickHandler = action -> { /* do something with action */ };
ui.onClick(clickHandler);
... and do the usual things we do with objects, like put them in collections:
Map<String,Consumer> handlers = new HashMap<>();
handlers.put("click", handleAction);
A BiFunction is just this with two input parameters. Let's use what we've seen so far to do something useful with BiFunctions:
Map<String,BiFunction<Integer,Integer,Integer>> operators = new HashMap<>();
operators.put("+", (a,b) -> a + b);
operators.put("-", (a,b) -> a - b);
operators.put("*", (a,b) -> a * b);
...
// get a, b, op from ui
ui.output(operators.get(operator).apply(a,b));
Baeldung
baeldung.com › home › java › core java › guide to java bifunction interface
Guide to Java BiFunction Interface | Baeldung
March 26, 2025 - We’ve looked at how to pass BiFunctions using lambdas and method references, and we’ve seen how to compose functions. The Java libraries only provide one- and two-parameter functional interfaces.
Oracle
docs.oracle.com › javase › 8 › docs › api › java › util › function › BiFunction.html
BiFunction (Java Platform SE 8 )
3 weeks ago - Returns a composed function that first applies this function to its input, and then applies the after function to the result. If evaluation of either function throws an exception, it is relayed to the caller of the composed function. ... Java™ Platform Standard Ed.
java - What do we need the BiFunction interface for? - Stack Overflow
The definition of the BiFunction interface contains a method apply(T t, U u), which accepts two arguments. However, I don't understand the use or purpose of this interface and method. What do we need More on stackoverflow.com
In what real scenario would one use BiFunction and TriFunction method?
Please ensure that: Your code is properly formatted as code block - see the sidebar (About on mobile) for instructions You include any and all error messages in full You ask clear questions You demonstrate effort in solving your question/problem - plain posting your assignments is forbidden (and such posts will be removed) as is asking for or giving solutions. Trying to solve problems on your own is a very important skill. Also, see Learn to help yourself in the sidebar If any of the above points is not met, your post can and will be removed without further warning. Code is to be formatted as code block (old reddit: empty line before the code, each code line indented by 4 spaces, new reddit: https://imgur.com/a/fgoFFis ) or linked via an external code hoster, like pastebin.com, github gist, github, bitbucket, gitlab, etc. Please, do not use triple backticks (```) as they will only render properly on new reddit, not on old reddit. Code blocks look like this: public class HelloWorld { public static void main(String[] args) { System.out.println("Hello World!"); } } You do not need to repost unless your post has been removed by a moderator. Just use the edit function of reddit to make sure your post complies with the above. If your post has remained in violation of these rules for a prolonged period of time (at least an hour), a moderator may remove it at their discretion. In this case, they will comment with an explanation on why it has been removed, and you will be required to resubmit the entire post following the proper procedures. To potential helpers Please, do not help if any of the above points are not met, rather report the post. We are trying to improve the quality of posts here. In helping people who can't be bothered to comply with the above points, you are doing the community a disservice. I am a bot, and this action was performed automatically. Please contact the moderators of this subreddit if you have any questions or concerns. More on reddit.com
10
14
February 21, 2021Is it possible to define a Java Function or BiFunction w/o lambda expression? - Stack Overflow
In Java, I have only ever defined "method references" Function and BiFunction w/ lambda expressions, like so: private static Function IsEvenFunc = ... More on stackoverflow.com
Partial Functions in Java 8
Essentially this is "the elvis operated" desugared slightly, and also almost feels like the beginning of a lens library maybe? I wonder if https://github.com/rocketscience-projects/javaslang has something covering this yet, the closest I can think off hand is the Try construct which is a monad wrapper for exception handling. More on reddit.com
9
8
January 22, 2015Videos
05:44
3.8 BiFunction Examples | What is BiFunction and how is is going ...
04:58
The Java BiFunction Functional Interface: Case Study ex11 - YouTube
00:44
What is a BiFunction? #java #shorts - YouTube
07:51
Java 8 Tutorial 10 :- BiPredicate Interface | BiFunction interface ...
TutorialsPoint
tutorialspoint.com › article › how-to-use-function-and-bifunction-interfaces-in-lambda-expression-in-java
How to use Function and BiFunction interfaces in lambda expression in Java?
July 13, 2020 - Java Object Oriented Programming Programming · The Function interface is a pre-defined functional interface that can be used as an assignment target for a lambda expression or method reference.
Medium
medium.com › @poojaauma › mastering-function-interfaces-in-java-beyond-basics-with-bifunction-noargsfunction-and-ed5c0892efd4
Mastering Function Interfaces in Java: Beyond Basics with BiFunction, NoArgsFunction, and TriFunction💻 | by Umadevi R | Medium
November 1, 2024 - Java’s Function and BiFunction interfaces are commonly used to represent functions that take one or two inputs and return a result.
GeeksforGeeks
geeksforgeeks.org › java › java-bifunction-interface-methods-apply-and-andthen
Java | BiFunction Interface methods - apply() and andThen()
July 11, 2025 - Note: The function being passed as the argument should be of type Function and not BiFunction. ... Parameters: This method accepts a parameter after which is the function to be applied after this function is one. Return Value: This method returns a composed function that first applies the current function first and then the after function. Exception: This method throws NullPointerException if the after function is null. ... // Java Program to demonstrate // BiFunction's andThen() method import java.util.function.BiFunction; public class Main { public static void main(String args[]) { // BiFunc
Top answer 1 of 3
25
The problem with this question is that it's not clear whether you see the purpose of a Function, which has a method apply(T t).
The value of all the functional types is that you can pass code around like data. One common use of this is the callback, and until Java 8, we used to have to do this with anonymous class declarations:
ui.onClick(new ClickHandler() {
public void handleAction(Action action) {
// do something in response to a click, using `action`.
}
}
Now with lambdas we can do that much more tersely:
ui.onClick( action -> { /* do something with action */ });
We can also assign them to variables:
Consumer clickHandler = action -> { /* do something with action */ };
ui.onClick(clickHandler);
... and do the usual things we do with objects, like put them in collections:
Map<String,Consumer> handlers = new HashMap<>();
handlers.put("click", handleAction);
A BiFunction is just this with two input parameters. Let's use what we've seen so far to do something useful with BiFunctions:
Map<String,BiFunction<Integer,Integer,Integer>> operators = new HashMap<>();
operators.put("+", (a,b) -> a + b);
operators.put("-", (a,b) -> a - b);
operators.put("*", (a,b) -> a * b);
...
// get a, b, op from ui
ui.output(operators.get(operator).apply(a,b));
2 of 3
3
One of usages of BiFunction is in the Map.merge method.
Here is an example usage of the Map.merge method, which uses a BiFunction as a parameter. What merge does is basically replaces the value of the given key with the given value if the value is null or the key does not have a value. Otherwise, replace the value of the given key after applying the BiFunction.
HashMap<String, String> map = new HashMap<>();
map.put("1", null);
map.put("2", "Hello");
map.merge("1", "Hi", String::concat);
map.merge("2", "Hi", String::concat);
System.out.println(map.get("1")); // Hi
System.out.println(map.get("2")); // HelloHi
If a BiFunction were not used, you would have to write a lot more code, even spanning several lines.
Here is a link that shows all the usages of BiFunction in the JDK: https://docs.oracle.com/javase/8/docs/api/java/util/function/class-use/BiFunction.html
Go check it out!
Educative
educative.io › answers › what-is-the-bifunction-functional-interface-in-java
What is the BiFunction functional interface in Java?
BiFunction is a functional interface, which accepts two arguments and returns a result. The interface contains two methods: ... The BiFunction interface is defined in the java.util.function package.
Medium
medium.com › @avinashsoni9829 › function-and-bi-function-in-java-java-internals-part-1-50363d25ba9a
Function and Bi Function in Java [ Java Internals Part — 1 ] | by Avinashsoni | Medium
December 29, 2022 - this again makes sure that the after function function input should be in sync with the output of the function1 which simply says that our after function would be applied after the first function ... default <V> BiFunction<T, U, V> andThen(Function<? super R, ?
YouTube
youtube.com › watch
Java 8 BiFunction Interface Tutorial with Examples | Lambda Expression - YouTube
In this video tutorial, you will learn how to use Java 8 BiFunction functional interface with lambda expression examples.In Java 8, BiFunction is a functiona...
Published April 28, 2020
Mkyong
mkyong.com › home › java8 › java 8 bifunction examples
Java 8 BiFunction Examples - Mkyong.com
February 29, 2020 - In Java 8, BiFunction is a functional interface; it takes two arguments and returns an object.
TopJavaTutorial
topjavatutorial.com › java-8 › java-8-bifunction-functional-interface
Java 8 : BiFunction Functional Interface - TopJavaTutorial
May 21, 2017 - The difference with Function is that while a Function takes a single parameter, a BiFunction takes 2 arguments. @FunctionalInterface public class BiFuntion { R apply(T t, U u); // Performs this operation on the given argument.
Reddit
reddit.com › r/javahelp › in what real scenario would one use bifunction and trifunction method?
r/javahelp on Reddit: In what real scenario would one use BiFunction and TriFunction method?
February 21, 2021 -
Hi all
I saw someone posted about trifunction and did some search about it, now I found out that there are BiFunction and TriFunction that it seems to be helping to write shorter code, that is all that I can summarize. But am I missing anything? What are the benefits of implementing this Bi/TriFunction model for coding Java in real application? Better performance (by much?), simpler codes?
Can someone help explain to me? Thank you in advance for you all.
PS: Sorry for the flair, I cannot seem to see the appropriate flair for this topic.
Top answer 1 of 4
6
TriFunctions are non standard and I haven't seen them actually used. The main purpose of them is to be functional interfaces for lambda expressions. BiFunctions are useful for doing reduce operations and for iterating over map key value pairs. For example, I could do the following: public class Polynomial{ private final double[] coefficients; public Polynomial(double... coefficients ){ this.coefficients = coefficients; } public double eval(double x){ return DoubleStram.of(coefficients).reduce(0d, (res, c) -> x * res + c); } } in which (res, c) -> x * res + c is a bi function as it takes to arguments and returns a value
2 of 4
2
BiFunctions are used in some parts of the Stream API to provide a convenient functional interface for e.g. reduction operations using lambdas. TriFunctions aren't part of the standard API but would ostensibly used for a similar purpose.
freeCodeCamp
freecodecamp.org › news › functional-programming-in-java
Functional Programming in Java
January 20, 2026 - The Java util package contains ... "BiFunction<A, B, C>". The Function interface takes a single input and produces an output, whereas the BiFunction interface takes two inputs and produces an output....
Top answer 1 of 2
3
You can write a class which implements that interface:
class MatchFirstChar implements Function<String,Boolean> {
private final char c;
MatchFirstChar(char c) {
this.c = c;
}
Boolean apply(String s) {
return s.charAt(0) == c;
}
}
and then use it:
System.out.println(names.toStringBy(new MatchFirstChar('J')));
This is more verbose than any of the other ways of doing this, but I think it introduces the minimum of new concepts.
2 of 2
2
You could always just define it as a regular function/method like this:
private static boolean IsEven(int i){
return i % 2 == 0;
}
private static boolean FirstChar(String s, char c){
return s.charAt(0) == c;
}
Medium
medium.com › @kavya1234 › understanding-bifunction-bipredicate-and-biconsumer-in-java-d980094adc00
Understanding BiFunction, BiPredicate and Biconsumer in Java | by Kavya | Medium
June 12, 2024 - BiFunction returns a result of type R. BiPredicate returns a boolean. BiConsumer does not return any result (void). ... These bi-functional interfaces are particularly useful when dealing with pairs of related objects or values, which is common in many real-world applications like e-commerce where you frequently deal with pairs like product and quantity, user and action, or price and discount.
Oracle
docs.oracle.com › en › java › javase › 11 › docs › api › java.base › java › util › function › BiFunction.html
BiFunction (Java SE 11 & JDK 11 )
January 20, 2026 - Package java.util.function · Type ... or method reference. @FunctionalInterface public interface BiFunction<T,U,R> Represents a function that accepts two arguments and produces a result....
Medium
medium.com › @rakesh.mali › java-8-function-and-bifunction-where-do-we-use-in-real-life-applications-846d5865650b
Java 8 Function and BiFunction — Where Do We Use in Real-Life Applications | by Rakesh Mali | Medium
April 15, 2025 - Using Function and BiFunction leads to cleaner, modular, and testable code. These functional interfaces help you express logic in a more declarative and reusable way, especially when paired with Streams, Lambdas, and method references. ... Delivery Lead | Mentor | IEEE Senior Member | SCRS Fellow | Java | Spring Boot|Angular|Full Stack|AWS|AI https://www.linkedin.com/in/rakesh-mali-25997098/
ConcretePage
concretepage.com › java › jdk-8 › java-8-biconsumer-bifunction-bipredicate-example
Java 8 BiConsumer, BiFunction and BiPredicate
All the three interface accepts two arguments. BiConsumer does not return any value but perform the defined operation. BiFunction returns a value. We define the data type for it while declaring BiFunction.
DZone
dzone.com › coding › java › be more functional: java's functional interfaces
Be More Functional: Java's Functional Interfaces - DZone
January 3, 2020 - However, keep in mind that the ... Function’s return type. ... BiFunction is similar to Function, except this accepts two input parameters as opposed to Function , which handles only one input....
Delft Stack
delftstack.com › home › howto › java › bifunction in java
BiFunction Interface in Java | Delft Stack
October 12, 2023 - Unlike the Function interface that takes two generics (one argument type and one return type), BiFunction takes two arguments and produces a result. We can assign a lambda expression or a method reference that takes two arguments and returns ...