函数式接口 @FunctionalInterface
package com.demo; import java.util.Arrays; import java.util.Comparator; public class Demo { public static void main(String[] args) { String[] array = new String[]{"pig", "cat", "dog"}; Arrays.sort(array, new Comparator<String>(){ @Override public int compare(String s1, String s2) { return s1.compareTo(s2); } }); System.out.println(Arrays.toString(array)); // [cat, dog, pig] } }
Lambda表达式
package com.demo; import java.util.Arrays; public class Demo { public static void main(String[] args) { String[] array = new String[]{"pig", "cat", "dog"}; Arrays.sort(array, (s1, s2) -> { return s1.compareTo(s2); }); System.out.println(Arrays.toString(array)); // [cat, dog, pig] } }
引用静态方法
package com.demo; import java.util.Arrays; public class Demo { public static void main(String[] args) { String[] array = new String[]{"pig", "cat", "dog"}; Arrays.sort(array, Demo::compareTo); System.out.println(Arrays.toString(array)); // [cat, dog, pig] } public static int compareTo(String s1, String s2){ return s1.compareTo(s2); } }
引用实例方法
// public int compareTo(String anotherString) // 相当于： // public static int compareTo(String this, String anotherString) Arrays.sort(array, String::compareTo);
引用构造方法
class Person { private String name; public Person(String name) { this.name = name; } }
package com.demo; import java.util.ArrayList; import java.util.Arrays; import java.util.List; public class Demo { public static void main(String[] args) { List<String> names = Arrays.asList("Tom", "Jack", "Steve"); List<Person> persons = new ArrayList<>(); for (String name : names) { persons.add(new Person(name)); } } }
简写
package com.demo; import java.util.Arrays; import java.util.List; import java.util.stream.Collectors; public class Demo { public static void main(String[] args) { List<String> names = Arrays.asList("Tom", "Jack", "Steve"); List<Person> persons = names.stream() .map(Person::new) .collect(Collectors.toList()); } }
创建Stream
String[] pets = new String[]{"pig", "dog", "cat"}; Stream<String> stream = Arrays.stream(pets); Stream<String> stream = Stream.of("pig", "dog", "cat"); Stream<String> stream = Arrays.asList("pig", "dog", "cat").stream();
// 映射 Stream<Integer> stream = Stream.of(1, 2, 3); stream.map(x -> x * x).forEach(System.out::println); // 1 4 9 // 过滤，留下偶数 Stream<Integer> stream = Stream.of(1, 2, 3); stream.filter(x -> x % 2 == 0).forEach(System.out::println); // 2 // 聚合 Stream<Integer> stream = Stream.of(1, 2, 3); int ret = stream.reduce(0, (sum, x) -> sum + x); System.out.println(ret); // 2
Stream提供的常用操作有：
转换操作：map()，filter()，sorted()，distinct()；
合并操作：concat()，flatMap()；
并行处理：parallel()；
聚合操作：reduce()，collect()，count()，max()，min()，sum()，average()；
其他操作：allMatch(), anyMatch(), forEach()。
