在Java中如何用lambda表达式实现IntFunction？

IntFunction接口是Java8中的函数接口，定义在java.util.function包中。此接口接受整值参数作为输入，并返回R类型的值。IntFunction接口可用作lambda表达式或引用方法的赋值目标，并且只包含一个抽象方法Apply()。

语法

@FunctionalInterface public interface IntFunction<R> { R apply(int value); }

示例

import java.util.HashMap; import java.util.Map; import java.util.function.IntFunction; public class IntFunctionTest { public static void main(String[] args) { IntFunction<String> getMonthName = monthNo -> { // lambda 表达式 Map<Integer, String> months = new HashMap<>(); months.put(1, "January"); months.put(2, "February"); months.put(3, "March"); months.put(4, "April"); months.put(5, "May"); months.put(6, "June"); months.put(7, "July"); months.put(8, "August"); months.put(9, "September"); months.put(10, "October"); months.put(11, "November"); months.put(12, "December"); if(months.get(monthNo)!= null) { return months.get(monthNo); } else { return "The number must between 1 to 12"; } }; int input = 1; String month = getMonthName.apply(input); System.out.println("Month number "+ input +" is: "+ month); input = 10; System.out.println("Month number "+ input +" is: "+ getMonthName.apply(input)); input = 15; System.out.println("Month number "+ input +" is: "+ getMonthName.apply(input)); } }

输出结果

Month number 1 is: JanuaryMonth number 10 is: OctoberMonth number 15 is: The number must between 1 to 12