functional programming - Functional Interfaces with More Arguments_java 8 function with more arguments-优快云博客

本文探讨了Java8中TriFunction接口的使用方法，通过具体示例展示了如何定义和使用带有三个参数的函数式接口。文章还讨论了lambda表达式的正确使用方式，以及类型不匹配时可能出现的编译错误。

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// functional/TriFunction.java
// (c)2017 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.

@FunctionalInterface
public interface TriFunction<T, U, V, R> {
  R apply(T t, U u, V v);
}

test above code:

// functional/TriFunctionTest.java
// (c)2017 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.

public class TriFunctionTest {
  static int f(int i, long l, double d) {
    return 99;
  }

  public static void main(String[] args) {
    TriFunction<Integer, Long, Double, Integer> tf = TriFunctionTest::f;
    tf = (i, l, d) -> 12; // [1]
    System.out.println(tf);
    System.out.println(tf.apply(1, 1L, 1.1));
  }
}
/* My Output:
TriFunctionTest$$Lambda$2/1915318863@4c873330
12
*/

when change [1] to

tf = (i, l, d) -> System.out.println(123);

It shows compile error:

functional/TriFunctionTest.java:13: error: incompatible types: bad return type in lambda expression
    tf = (i, l, d) -> System.out.println("123");
                                        ^
    void cannot be converted to Integer
1 error

references:

1. On Java 8 - Bruce Eckel

2. https://stackoverflow.com/questions/18400210/java-8-where-is-trifunction-and-kin-in-java-util-function-or-what-is-the-alt

3. https://github.com/wangbingfeng/OnJava8-Examples/blob/master/functional/TriFunction.java

4. https://github.com/wangbingfeng/OnJava8-Examples/blob/master/functional/TriFunctionTest.java