java lambda表达式示例

落日映苍穹つ 2022-06-14 11:12 211阅读 0赞

# java lambda表达式示例 #

1、本文主要介绍lambda表达式的使用。

package com.xueyou.demo.lambda;
    
    import org.junit.Test;
    
    import java.util.Arrays;
    import java.util.IntSummaryStatistics;
    import java.util.List;
    import java.util.function.Predicate;
    import java.util.stream.Collectors;
    
    public class LambdaTest {
        @Test
        public void tt() {
            //foreach 使用
            List<String> list = Arrays.asList("23", "2622", "3", "4444444");
            System.out.println("======foreach的使用======");
            list.forEach(x -> System.out.print(x + "\t"));
            System.out.println("");
            list.forEach(x -> System.out.print(x.length() + "\t"));
            System.out.println("");
            list.forEach(x -> System.out.print(dealStr(x) + "\t"));
            System.out.println("");
    
    
            //filter的使用
            System.out.println("======filter的使用======");
            list.stream().filter(new Predicate<String>() {
                @Override
                public boolean test(String s) {
                    if (Integer.valueOf(s) > 100) {
                        return true;
                    } else {
                        return false;
                    }
                }
            }).forEach(x -> System.out.print(x + "\t"));
            System.out.println("");
    
            list.stream().filter(this::selfCondition).forEach(x -> System.out.print(x + "\t"));
            System.out.println("");
    
            //返回长度大于1且长度小于5的
            System.out.println("filter返回长度在1和5之间的数据");
            Predicate<String> lenthBiggerThan1 = (n) -> n.length() > 1;
            Predicate<String> lenthLessThan5 = (n) -> n.length() < 5;
            list.stream().filter(lenthBiggerThan1.and(lenthLessThan5)).forEach(x -> System.out.print(x + "\t"));
            System.out.println("");
    
            //过滤后转换成新的List
            System.out.println("过滤后生成一个新的list");
            List<String> newList = list.stream().filter(lenthBiggerThan1.and(lenthLessThan5)).collect(Collectors.toList());
            newList.forEach(x -> System.out.print(dealStr(x) + "\t"));
            System.out.println("");
    
            //map使用
            System.out.println("======map使用======");
            list.stream().map(x -> Integer.valueOf(x.toString()) * 2).forEach(x -> System.out.print(x + "\t"));
            System.out.println("");
            //这里传递的参数是一个函数，这个函数把String转换成任意类型
            list.stream().map(this::strToInt).forEach(x -> System.out.print(x + "\t"));
            System.out.println("");
    
            //map之后，生成一个新的list
            System.out.println("======map之后，生成一个新的list======");
            List<Integer> newIntList = list.stream().map(this::strToInt).collect(Collectors.toList());
            newIntList.forEach(x -> System.out.print(x + "\t"));
            System.out.println("");
    
    
            //统计
            System.out.println("======统计最大值最小值等======");
            List<Integer> primes = Arrays.asList(2, 3, 5, 7, 11, 13, 17, 19, 23, 29);
            IntSummaryStatistics statistics = primes.stream().mapToInt((x) -> x).summaryStatistics();
            System.out.println(statistics.getAverage());
            System.out.println(statistics.getCount());
            System.out.println(statistics.getMax());
            System.out.println(statistics.getMin());
            System.out.println(statistics.getSum());
        }
    
        public String dealStr(String str) {
            return str + "xxxx";
        }
    
        public boolean selfCondition(String s) {
            if (Integer.valueOf(s) > 100) {
                return true;
            } else {
                return false;
            }
        }
    
        public int strToInt(String c) {
            return Integer.valueOf(c);
        }
    
    }

运行结果：

![Center][]

多余的不解释，看上边的程序和执行结果。

[Center]: /images/20220614/ceafbbf47be74f27941d070d252a55e5.png