前言
Lambda表达式是一种在古代编程语言中越来越常见的个性，能够简化代码、进步生产力。这篇文章将介绍10个必须把握的Lambda表达式，这些表达式涵盖了在理论编程中常常用到的常见场景，例如列表操作、函数组合、条件筛选等。通过学习这些Lambda表达式，你将更加深刻地了解函数式编程的思维，可能更加高效地编写代码。
1. 应用Lambda表达式进行汇合遍历
未应用Lambda表达式：
List<String> list = Arrays.asList("apple", "banana", "orange");for (String fruit : list) { System.out.println(fruit);}应用Lambda表达式：
List<String> list = Arrays.asList("apple", "banana", "orange");list.forEach(fruit -> System.out.println(fruit));2. 应用Lambda表达式进行排序
未应用Lambda表达式：
List<String> list = Arrays.asList("apple", "banana", "orange");Collections.sort(list, new Comparator<String>() { public int compare(String s1, String s2) { return s1.compareTo(s2); }});应用Lambda表达式：
List<String> list = Arrays.asList("apple", "banana", "orange");Collections.sort(list, (s1, s2) -> s1.compareTo(s2));3. 应用Lambda表达式进行过滤
未应用Lambda表达式：
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); }}应用Lambda表达式：
List<String> list = Arrays.asList("apple", "banana", "orange");List<String> filteredList = list.stream().filter(fruit -> fruit.startsWith("a")).collect(Collectors.toList());4. 应用Lambda表达式进行映射
未应用Lambda表达式：
List<String> list = Arrays.asList("apple", "banana", "orange");List<Integer> lengths = new ArrayList<Integer>();for (String fruit : list) { lengths.add(fruit.length());}应用Lambda表达式：
List<String> list = Arrays.asList("apple", "banana", "orange");List<Integer> lengths = list.stream().map(fruit -> fruit.length()).collect(Collectors.toList());5. 应用Lambda表达式进行归约
未应用Lambda表达式：
List<Integer> list = Arrays.asList(1, 2, 3, 4, 5);int sum = 0;for (int i : list) { sum += i;}应用Lambda表达式：
List<Integer> list = Arrays.asList(1, 2, 3, 4, 5);int sum = list.stream().reduce(0, (a, b) -> a + b);6. 应用Lambda表达式进行分组
未应用Lambda表达式：
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);}应用Lambda表达式：
List<String> list = Arrays.asList("apple", "banana", "orange");Map<Integer, List<String>> grouped = list.stream().collect(Collectors.groupingBy(fruit -> fruit.length()));7. 应用Lambda表达式进行函数式接口的实现
未应用Lambda表达式：
public interface MyInterface { public void doSomething(String input);}MyInterface myObject = new MyInterface() { public void doSomething(String input) { System.out.println(input); }};myObject.doSomething("Hello World");应用Lambda表达式：
MyInterface myObject = input -> System.out.println(input);myObject.doSomething("Hello World");8. 应用Lambda表达式进行线程的创立
未应用Lambda表达式：
Thread thread = new Thread(new Runnable() { public void run() { System.out.println("Thread is running."); }});thread.start();应用Lambda表达式：
Thread thread = new Thread(() -> System.out.println("Thread is running."));thread.start();9. 应用Lambda表达式进行Optional的操作
未应用Lambda表达式：
String str = "Hello World";if (str != null) { System.out.println(str.toUpperCase());}应用Lambda表达式：
Optional<String> str = Optional.ofNullable("Hello World");str.map(String::toUpperCase).ifPresent(System.out::println);10. 应用Lambda表达式进行Stream的流水线操作
未应用Lambda表达式：
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);应用Lambda表达式：
List<String> list = Arrays.asList("apple", "banana", "orange");List<String> filteredList = list.stream().filter(fruit -> fruit.startsWith("a")).map(String::toUpperCase).sorted().collect(Collectors.toList());结尾
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