Functions cheat sheet
Functional interface will have single abstract method and they provide target types for lambda expressions. There are many functional interfaces in Java and they all are available in java.util.function package. I tried to organize all of them with a logical diagram and table. Table contains interface name and abstract method. You can refer this article to get an idea of available functions and its variants.
Consumer
Consumer takes input and always returns void. You can use this to perform some action with out returning anything.
| Consumer | void accept(T t) |
| DoubleConsumer | void accept(double value) |
| IntConsumer | void accept(int value) |
| LongConsumer | void accept(long value) |
| BiConsumer | void accept(T t, U t) |
| ObjDoubleConsumer | void accept(T t, double value) |
| ObjIntConsumer | void accept(T t, int value) |
| ObjLongConsumer | void accept(T t, long value) |
Function
Function takes input and produces different kind of output.
| Function | R apply(T t) |
| IntFunction | R apply(int value) |
| LongFunction | R apply(long value) |
| DoubleFunction | R apply(double value) |
| DoubleToIntFunction | int applyAsInt(double value) |
| DoubleToLongFunction | long applyAsLong(double value) |
| IntToDoubleFunction | double applyAsDouble(int value) |
| IntToLongFunction | long applyAsLong(int value) |
| LongToDoubleFunction | double applyAsDouble(long value) |
| LongToIntFunction | int applyAsInt(long value) |
| ToDoubleFunction | double applyAsDouble(T value) |
| ToIntFunction | int applyAsInt(T value) |
| ToLongFunction | long applyAsLong(T value) |
| BiFunction | R apply(T t, U t) |
| ToDoubleBiFunction | double applyAsDouble(T t, U t) |
| ToIntBiFunction | int applyAsInt(T t, U t) |
| ToLongBiFunction | long applyAsLong(T t, U t) |
Operator
Operator is a special kind of function where it always accepts and produces same type.
| UnaryOperator | T apply(T t) |
| DoubleUnaryOperator | double applyAsDouble(double operand) |
| IntUnaryOperator | int applyAsInt(int operand) |
| LongUnaryOperator | long applyAsLong(long operand) |
| BinaryOperator | R apply(T t, U t) |
| DoubleBinaryOperator | double applyAsDouble(double left, double right) |
| IntBinaryOperator | int applyAsInt(int left, int right) |
| LongBinaryOperator | long applyAsLong(long left, long right) |
Predicate
Predicate always returns a boolean so you can this in conditional evaluations.
| Predicate | boolean test(T t) |
| DoublePredicate | boolean test(double value) |
| IntPredicate | boolean test(int t) |
| LongPredicate | boolean test(long t) |
| BiPredicate | boolean test(T t, U u) |
Supplier
Supplier always returns a value. This can be used to generate random values or data from some source.
| Supplier | T get() |
| BooleanSupplier | boolean getAsBoolean() |
| DoubleSupplier | double getAsDouble() |
| IntSupplier | int getAsInt() |
| LongSupplier | long getAsLong() |