Java8 lambda表达式详解

Java8 lambda表达式详解

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Java8 lambda表达式详解

下文笔者讲述Java8中lambda的简介说明,如下所示:

实现Runnable线程

可以使用下面语法实现Lambda:

 (params) -> expression(params) -> statement(params) -> { statements }

例

方法接受两个方法参数
(int t1, int t2) -> t1 + t2
可简写
(int a, int b) -> a + b

例: 多线程示例

Java8之前
new Thread(new Runnable() {@Overridepublic void run() {System.out.println("Java8之前代码写法!");}
}).start();Java8:new Thread(() -> System.out.println("java8")).start();

遍历List集合

Java8 之前
List<String> numbers = Arrays.asList("j", "a", "v", "a");
for (String number : numbers) {System.out.println(number);
}Java8:
List<String> numbers = Arrays.asList("j", "a", "v", "a");
numbers.forEach(n -> System.out.println(n));或使用方法引用操作符号“::”
List<String> numbers = Arrays.asList("j", "a", "v", "a");
numbers.forEach(System.out::println);

使用过滤方法

filter过滤数组中大于3的数字
List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5);
numbers.stream().filter((n) -> n > 3).forEach(System.out::println);

复杂的条件

java.util.function.Predicate提供and(), or() 和 xor()可以进行逻辑操作。List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5);
Predicate<Integer> greater2 = (n) -> n > 2;
Predicate<Integer> less4 = (n) -> n < 4;
numbers.stream().filter(greater2.and(less4)).forEach(System.out::println);

实现 Map 和 Reduce

.map 改变集合元素List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5);
numbers.stream().map((n) -> n * n).forEach(System.out::println);.reduce 将计算集合中所有值。List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5);
Integer count = numbers.stream().map((n) -> n * n).reduce((sum, n) -> sum + n).get();
System.out.println(count);

集合转换

.collect 变为另一个集合。List<Integer> oldNumbers = Arrays.asList(1, 2, 3, 4, 5);
List<Integer> list = oldNumbers.stream().map((n) -> n * n).List());
list.forEach(System.out::println);

整合集合中所有元素为一个字符串

将字符串转换为大写
使用逗号串起来
List<String> strList = Arrays.asList("j", "a", "v","a");
String str = strList.stream().map(String::toUpperCase).collect(Collectors.joining(", "));
System.out.println(str);

去除重复的元素

distinct()去除重复元素List<String> stringList = Arrays.asList("a", "b", "c", "a", "b");
String str = stringList.stream().map(String::toUpperCase).distinct().collect(Collectors.joining(", "));
System.out.println(str);

计算List中元素的最大值，最小值，和，平均值

List<Integer> numbers = Arrays.asList(2, 3, 5, 7, 11, 12, 14, 16, 17, 18);
IntSummaryStatistics stats = numbers.stream().mapToInt((x) -> x).summaryStatistics();
System.out.println("集合中最大值 : " + Max());
System.out.println("集合中最小值 : " + Min());
System.out.println("集合中元素之和 : " + Sum());
System.out.println("集合中元素平均值 : " + Average());

排序

创建三个 User 对象，进行姓名排序。List<User> userList = Arrays.asList(new User("A", 12, Sex.MAN, 2011, 60.5, Arrays.asList("swim","running")),new User("C", 23, Sex.MAN, 2012, 54.3, Arrays.asList("music","riding")),new User("B", 30, Sex.WOMAN, 2010, 48.2, Arrays.asList("swim","programme"))
);userList.stream().sorted(Comparatorparing(User::getName)).forEach(System.out::println);

取最小值

取最小值，不为空则打印
List<User> userList = Arrays.asList(new User("A", 12, Sex.MAN, 2011, 60.5, Arrays.asList("swim","running")),new User("C", 23, Sex.MAN, 2012, 54.3, Arrays.asList("music","riding")),new User("B", 30, Sex.WOMAN, 2010, 48.2, Arrays.asList("swim","programme"))
);userList.stream().min(Comparatorparing(User::getAge)).ifPresent(System.out::println);

取其中一个字段并排序

取其中一个字段并排序
List<User> userList = Arrays.asList(new User("A", 12, Sex.MAN, 2011, 60.5, Arrays.asList("swim","running")),new User("C", 23, Sex.MAN, 2012, 54.3, Arrays.asList("music","riding")),new User("B", 30, Sex.WOMAN, 2010, 48.2, Arrays.asList("swim","programme"))
);userList.stream().map(User::getName).sorted().forEach(System.out::println);

是否符合条件

allMatch是否全部符合条件，是则返回true,但凡有一个不满足则返回false.List<User> userList = Arrays.asList(new User("A", 12, Sex.MAN, 2011, 60.5, Arrays.asList("swim","running")),new User("C", 23, Sex.MAN, 2012, 54.3, Arrays.asList("music","riding")),new User("B", 30, Sex.WOMAN, 2010, 48.2, Arrays.asList("swim","programme"))
);boolean tmp = userList.stream().allMatch(u -> u.getAge() < 35);
System.out.println(tmp);