十个必须掌握的lambda表达式，一行代码写一个逻辑，简化代码堪比Python

?好处

1. 简洁：lambda表达式可以使代码更加简洁，减少冗余的匿名内部类。
2. 函数式编程：lambda表达式支持函数式编程，可以方便地将函数作为参数传递给其他方法。
3. 并行处理：lambda表达式可以与Java 8中的Stream API结合使用，实现并行处理，提高程序性能。
4. 延迟执行：lambda表达式可以实现延迟执行，只有在需要时才会执行相应的操作。
5. 易于阅读：lambda表达式的语法更加清晰，易于阅读和理解。

举例子对比

假设我们有一个需求，需要对一个整数列表进行排序，可以使用传统的匿名内部类实现

List<Integer> numbers = Arrays.asList(5, 3, 8, 1, 6); 
numbers.sort(new Comparator<Integer>() {
 @Override
 public int compare(Integer o1, Integer o2) { return o1 - o2; } 
});

使用Lambda表达式后，代码变得更加简洁：

List<Integer> numbers = Arrays.asList(5, 3, 8, 1, 6); 
numbers.sort((o1, o2) -> o1 - o2);

另外，Lambda表达式还可以用于实现Runnable接口，例如：

Runnable runnable = () -> System.out.println("Hello, World!"); runnable.run();

从上面可以看出使用lambda表达式之后对于可读性和代码简洁度方面都有提升。

十种用法

那么以下举一些用法：

1. 使用Lambda表达式进行集合遍历

List<String> list = Arrays.asList("apple", "banana", "orange");

for (String fruit : list) {

System.out.println(fruit);

}

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List<String> list2 = Arrays.asList("apple", "banana", "orange");

list2.forEach(fruit -> System.out.println(fruit));

?2. 使用Lambda表达式进行排序

?List<String> list2 = Arrays.asList("apple", "banana", "orange");

?Collections.sort(list2, new Comparator<String>() {

?public int compare(String s1, String s2) {

?return s1.compareTo(s2);

?}

?});

?List<String> list = Arrays.asList("apple", "banana", "orange");

?Collections.sort(list, (s1, s2) -> s1.compareTo(s2));

?

?3. 使用Lambda表达式进行过滤

List<String> list = Arrays.asList("apple", "banana", "orange");

?List<String> filteredList = new ArrayList<String>();

?for (String fruit : list) {

?if (fruit.startsWith("a")) {

?filteredList.add(fruit);

?}

?}

?List<String> list2 = Arrays.asList("apple", "banana", "orange");

?List<String> filteredLists = list2.

?stream().

?filter(fruit -> fruit.startsWith("a")).

?collect(Collectors.toList());

?

?4. 使用Lambda表达式进行映射

List<String> list = Arrays.asList("apple", "banana", "orange");

?List<Integer> lengths = new ArrayList<Integer>();

?for (String fruit : list) {

?lengths.add(fruit.length());

?}

?List<String> lists = Arrays.asList("apple", "banana", "orange");

?List<Integer> lengthss = lists.stream().map(fruit -> fruit.length())

?.collect(Collectors.toList());

?

?5. 使用Lambda表达式进行归约

List<Integer> list = Arrays.asList(1, 2, 3, 4, 5);

?int sum = 0;

?for (int i : list) {

?sum += i;

?}

?

?List<Integer> list2 = Arrays.asList(1, 2, 3, 4, 5);

?int sum2 = list2.stream().reduce(0, (a, b) -> a + b);

? ?

?6. 使用Lambda表达式进行分组

?List<String> list = Arrays.asList("apple", "banana", "orange");

?Map<Integer, List<String>> grouped = new HashMap<Integer, List<String>>();

?for (String fruit : list) {

?int length = fruit.length();

?if (!grouped.containsKey(length)) {

?grouped.put(length, new ArrayList<String>());

?}

?grouped.get(length).add(fruit);

?}

?List<String> lists = Arrays.asList("apple", "banana", "orange");

?Map<Integer, List<String>> groupeds = lists.stream().collect(Collectors.groupingBy(fruit -> fruit.length()));

?

?7. 使用Lambda表达式进行函数式接口的实现

MyInterface myObject = new MyInterface() {

?public void doSomething(String input) {

?System.out.println(input);

?}

?};

?myObject.doSomething("Hello World");

?MyInterface myObject = input -> System.out.println(input);

?myObject.doSomething("Hello World");

?

8. 使用Lambda表达式进行线程的创建

Thread thread = new Thread(new Runnable() {

?public void run() {

?System.out.println("Thread is running.");

?}

?});

?thread.start();

?Thread threads = new Thread(() -> System.out.println("Thread is running."));

?threads.start();

?

?9. 使用Lambda表达式进行Optional的操作

?String str = "Hello World";

?if (str != null) {

?System.out.println(str.toUpperCase());

?}

?Optional<String> strs = Optional.ofNullable("Hello World");

?strs.map(String::toUpperCase).ifPresent(System.out::println);

?

?10. 使用Lambda表达式进行Stream的流水线操作

List<String> list = Arrays.asList("apple", "banana", "orange");

List<String> filteredList = new ArrayList<String>();

for (String fruit : list) {

if (fruit.startsWith("a")) {

filteredList.add(fruit.toUpperCase());

}

}

Collections.sort(filteredList);

List<String> lists = Arrays.asList("apple", "banana", "orange");

List<String> filteredLists = lists.stream().filter(fruit -> fruit.startsWith("a")).map(String::toUpperCase).sorted().collect(Collectors.toList());

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