前语
Lambda表达式是一种在现代编程语言中越来越常见的特性，能够简化代码、提高生产力。这篇文章将介绍10个有必要掌握的Lambda表达式，这些表达式涵盖了在实际编程中经常用到的常见场景，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，你将愈加深化地了解函数式编程的思维，能够愈加高效地编写代码。
1. 运用Lambda表达式进行集合遍历
未运用Lambda表达式：
List<String> list = Arrays.asList("apple", "banana", "orange");
for (String fruit : list) {
System.out.println(fruit);
}
运用Lambda表达式：
List<String> list = Arrays.asList("apple", "banana", "orange");
list.forEach(fruit -> System.out.println(fruit));
2. 运用Lambda表达式进行排序
未运用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);
}
});
运用Lambda表达式：
List<String> list = Arrays.asList("apple", "banana", "orange");
Collections.sort(list, (s1, s2) -> s1.compareTo(s2));
3. 运用Lambda表达式进行过滤
未运用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);
}
}
运用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. 运用Lambda表达式进行映射
未运用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());
}
运用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. 运用Lambda表达式进行归约
未运用Lambda表达式：
List<Integer> list = Arrays.asList(1, 2, 3, 4, 5);
int sum = 0;
for (int i : list) {
sum += i;
}
运用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. 运用Lambda表达式进行分组
未运用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);
}
运用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. 运用Lambda表达式进行函数式接口的完成
未运用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");
运用Lambda表达式：
MyInterface myObject = input -> System.out.println(input);
myObject.doSomething("Hello World");
8. 运用Lambda表达式进行线程的创立
未运用Lambda表达式：
Thread thread = new Thread(new Runnable() {
public void run() {
System.out.println("Thread is running.");
}
});
thread.start();
运用Lambda表达式：
Thread thread = new Thread(() -> System.out.println("Thread is running."));
thread.start();
9. 运用Lambda表达式进行Optional的操作
未运用Lambda表达式：
String str = "Hello World";
if (str != null) {
System.out.println(str.toUpperCase());
}
运用Lambda表达式：
Optional<String> str = Optional.ofNullable("Hello World");
str.map(String::toUpperCase).ifPresent(System.out::println);
10. 运用Lambda表达式进行Stream的流水线操作
未运用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);
运用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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