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Lambda 表达式的常见用法

使用Lambda表达式集合遍历

/*遍历集合*/
List<String> fruitList = Arrays.asList("apple","banana","orange","mango","grape");
//传统方式
for (String s : fruitList) {System.out.println(s);
}
//lambda
fruitList.forEach(System.out::println);

使用Lambda表达式排序

        /*集合排序*/List<String> fruitList = Arrays.asList("apple","banana","orange","mango","grape");//传统方式Collections.sort(fruitList, new Comparator<String>() {@Overridepublic int compare(String o1, String o2) {return o1.compareTo(o2);}});//lambdaCollections.sort(fruitList, ((o1, o2) -> o1.compareTo(o2)));

使用Lambda表达式过滤

        /*集合过滤 拿到首字母是 a 的元素*/List<String> fruitList = Arrays.asList("apple","banana","orange","mango","grape");//传统List<String> list1 = new ArrayList<>();for (String s : fruitList) {if (s.startsWith("a")) {list1.add(s);}}//lambdaList<String> list2 = fruitList.stream().filter(s -> s.startsWith("a")).collect(Collectors.toList());

使用Lambda表达式映射

        /*集合映射 映射出字段的长度*/List<String> fruitList = Arrays.asList("apple","banana","orange","mango","grape");//传统List<Integer> list1 = new ArrayList<>();for (String s : fruitList) {list1.add(s.length());}//lambdaList<Integer> list2 = fruitList.stream().map(s -> s.length()).collect(Collectors.toList());

使用Lambda表达式归约

        /*集合归约 list 所有字段累加*/List<Integer> sumList = Arrays.asList(1,2,3,4,5,6,8);//传统int sum1 = 0;for (Integer v : sumList) {sum1 += v;}//lambdaInteger sum2 = sumList.stream().reduce(0, (a, b) -> a + b);

使用Lambda表达式分组

        /*集合分组 list字段的长度进行分组*/List<String> fruitList = Arrays.asList("apple","banana","orange","mango","grape");//传统Map<Integer, List<String>> group1 = new HashMap<>();for (String s : fruitList) {if (!group1.containsKey(s.length())){group1.put(s.length(), new ArrayList<>());}group1.get(s.length()).add(s);}//lambdaMap<Integer, List<String>> group2 = fruitList.stream().collect(Collectors.groupingBy(String::length));

使用Lambda表达式函数式接口的实现

        //接口interface MyInterface {public void doSomething(String s);}/*实现接口*///传统方法MyInterface myInterface1 = new MyInterface() {@Overridepublic void doSomething(String s) {System.out.println(s);}};//lambdaMyInterface myInterface2 = (s) -> System.out.println(s);//或者MyInterface myInterface3 = System.out::println;

使用Lambda表达式线程的创建

        /*创建线程  实际开发中不要显示创建线程，最好用线程池*///传统Thread thread = new Thread(new Runnable() {@Overridepublic void run() {System.out.println("Hello World");}});thread.start();//lambdaThread thread1 = new Thread(() -> System.out.println("Hello World"));Thread thread2 = new Thread(System.out::println);Thread thread3 = new Thread(LambdaUsefullness::listreduceSum);

/*使用线程池举例*/ThreadPoolExecutor executor = new ThreadPoolExecutor(2, 5, 2L, TimeUnit.SECONDS, new LinkedBlockingDeque<>(4), Executors.defaultThreadFactory(), new ThreadPoolExecutor.AbortPolicy());executor.execute(() ->{for (int i = 0; i < 10 ; i++) {System.out.println("Hello World分支线程===="+i);}});

使用Lambda表达式进行Optional 操作

        /*Lambda 方式配合Optional 操作*/String str = "Hello world";//传统校验if (!str.isEmpty()) {System.out.println(str.toUpperCase());}//lambdaOptional.ofNullable(str).map(String::toUpperCase).ifPresent(System.out::println);

使用Lambda表达式进行Stream的流操作

        /*lambda流操作 过滤包含 n 的字符串，并转大写，最后排序*/List<String> fruitList = Arrays.asList("apple","banana","orange","mango","grape");//传统List list1 = new ArrayList();for (String s : fruitList) {if (s.contains("n")) {list1.add(s.toUpperCase());}}Collections.sort(list1);//lambdaList<String> list2 = fruitList.stream().filter(s -> s.contains("n")).map(String::toUpperCase).sorted().collect(Collectors.toList());