java lambda常用api

柔情只为你懂 2023-06-07 10:53 47阅读 0赞

** 1、循环遍历**

** **      和普通for循环一样，如果在循环内部没有通讯相关的耗时操作，建议使用原始的for循环。

lists.stream().forEach(l->{
          System.out.println(l);
     });

Map<String,String> map =  new HashMap<>();
    map.forEach((k,v)->{
         System.out.println(k);
         System.out.println(v);
    });

**2、函数式接口**

@FunctionalInterface
    public interface Callback {
    
        void  callback();
    }

public static void addCallback(Callback callback){
          callback.callback();
     }

addCallback(()->{
         System.out.println("12345");
     });

**3、mapping获取  获取集合对象中指定属性的值**

List<String> names = tests.stream().map(Test::getName).collect(Collectors.toList());

**4、filter过滤  过滤集合对象中指定存在某些规则的对象**

List<Order> ret = orders.stream().filter(o->o.getPrice() > 10).collect(Collectors.toList());

过滤订单集合中价格大于10的订单，返回集合

**5、列表每个元素应用函数**

List<String> G7 = Arrays.asList("USA", "Japan", "France", "Germany", "Italy", "U.K.","Canada");
    String G7Countries = G7.stream().map(x -> x.toUpperCase()).collect(Collectors.joining(", "));

**6、去除重复**

List<String> strs = Lists.newArrayList("12","13","12","13");
    strs = strs.stream().distinct().collect(Collectors.toList());

**7、计算集合中最大值，最小值，总和，平均值**

List<Integer> primes = Arrays.asList(2, 3, 5, 7, 11, 13, 17, 19, 23, 29);
    IntSummaryStatistics stats = primes.stream().mapToInt((x) -> x).summaryStatistics();
    System.out.println("Highest prime number in List : " + stats.getMax());
    System.out.println("Lowest prime number in List : " + stats.getMin());
    System.out.println("Sum of all prime numbers : " + stats.getSum());
    System.out.println("Average of all prime numbers : " + stats.getAverage());

**8、分组**

Test test = new Test("apple",1);
    Test test1 = new Test("apple",2);
    Test test2 = new Test("apple",3);
    
    Test test3 = new Test("date",3);
    Test test4 = new Test("date",4);
    List<Test> tests = Lists.newArrayList(test,test1,test2,test3,test4);
    Map<String,List<Integer>> value = tests.stream().
                    collect(Collectors.groupingBy(Test::getName, Collectors.mapping(Test::getPrice,Collectors.toList())));
    Map<String,IntSummaryStatistics> result = tests.stream().
                    collect(Collectors.groupingBy(Test::getName, Collectors.summarizingInt(Test::getPrice)));