1、【Functional Interface】:一個接口僅有一個抽象方法,比如Runnable、Comparator等。在任何一個需要Functional Interface對象的地方,都可以使用lambda表達式。
2、【Method Reference】:將lambda表達式的參數作爲參數傳遞給一個方法,他們的執行效果是相同的,則該lambda表達式
可以使用Method Reference表達,以下兩種方式是等價的:
(x) -> System.out.println(x)
System.out::println
Method Reference主要有三種形式:
1.Object::instanceMethod
2.Class::staticMethod
3.Class::instanceMethod
對於前兩種方式,對應的lambda表達式的參數和method的參數是一致的,比如:
System.out::println
(x) -> System.out.println(x)
Math::pow
(x, y) -> Math.pow(x, y)
對於第三種方式,對應的lambda表達式的語句體中,第一個參數作爲對象,調用method,將其它參數
String::compareToIgnoreCase
(s1, s2) -> s1.compareToIgnoreCase(s2)
Constructor Reference與Method Reference類似,只不過是特殊的method:new,具體調用的是哪個構造函數,由上下文環境決定,比如:
List<String> labels = ...;
Stream<Button> stream = labels.stream().map(Button::new);
Button::new等價於(x) -> Button(x),所以調用的構造函數是:Button(x);
除了創建單個對象,也可以創建對象數組,如下面兩種方式等價:
int[]::new
(x) -> new int[x]
====== Map ======
1、map遍歷
itemsMap.forEach((k,v)->System.out.println("Item : " + k + " Count : " + v));
====== List ======
1、List排序
1)、list升序
//原始版
words.sort((Word first, Word second) -> first.getName().compareTo(second.getName()));
//精簡版
Collections.sort(words, Comparator.comparing(Word::getName));
//精簡版,推薦使用這種
words.sort(Comparator.comparing(Word::getName));
//多重排序(連個都升序)
words.sort(Comparator.comparing(Word::getName).thenComparingInt(Word::getCountry));
//多重排序(第一個升,第二個降)
words.sort(Comparator.comparing(Word::getName).reversed().thenComparingInt(Word::getCountry).reversed());
2)、list降序
words.sort(Comparator.comparing(Word::getName).reversed());
2、list遍歷
words.forEach(System.out::println);
3、list轉Map(key去重)
Map<String, Word> wordMapMap = wordList.stream().collect(Collectors.toMap(Word::getName, k -> k, (k1, k2) -> k1));
list轉Map(key不能重複)
Map<Integer,Word> userMap = wordList.stream().collect(Collectors.toMap(Word::getCountry, k -> k));
4、分組
Map<String, List<Word>> groupMap = wordList.stream().collect(Collectors.groupingBy(Word::getName));
多重分組
Map<String, Map<Integer, List<Word>>> map2 = words.stream().collect(Collectors.groupingBy(Word::getName,Collectors.groupingBy(Word::getCountry)));
5、匹配過濾
List<Word> filterList = wordList.stream().filter(v -> v.getName().equals("tiger")).collect(Collectors.toList());
wordList.stream().filter(v -> v.getName().contains("老")).forEach(System.out::println);
List<Word> filterList = wordList.stream().filter(v -> v.getCountry() > 2).collect(Collectors.toList());
Predicate<Word> equals1 = v -> v.getCountry().equals(1);
Predicate<Word> contains1 = v -> v.getName().contains("tiger");
List<Word> filterList = wordList.stream().filter(contains1.and(equals1)).collect(Collectors.toList());
List<Double> filteredCost = cost.stream().filter(x -> x > 25.0).collect(Collectors.toList());
6、list統計求和
int sum = wordList.stream().mapToInt(Word::getCountry).sum();
double sum = words.stream().mapToDouble(Word::getCountry).sum();
7、分組統計個數
Map<String, Long> collectCnt = wordList.stream().collect(Collectors.groupingBy(Word::getName, Collectors.counting()));
8、分組統計
Map<String, LongSummaryStatistics> map3 = words.stream().collect(Collectors.groupingBy(Word::getName,Collectors.summarizingLong(Word::getCountry)));
多重分組統計
Map<String, Map<Integer, LongSummaryStatistics>> map3 = words.stream().collect(Collectors.groupingBy(Word::getName,Collectors.groupingBy(Word::getCountry,Collectors.summarizingLong(Word::getCountry))));
9、去重(需根據實際情況重寫Word的equals與hashCode)
List<Word> list1= list.stream().distinct().collect(Collectors.toList());
10、數據拼裝
String result = words.stream().map(Word::getName).collect(Collectors.joining("," , "[" , "]"));
12、對象集合轉屬性集合
List<String> result = words.stream().map(Word::getName).collect(Collectors.toList());
List<String> result = words.stream().map(y -> y.getName().concat(".jpg")).collect(Collectors.toList());
====== 數組 ======
1、數組排序
1)、數組升序->原始版
Arrays.sort(people, (first, second) -> Integer.compare(first.length(), second.length()));
數組升序->精簡版
Arrays.sort(people, Comparator.comparingInt(String::hashCode));
2)、數組降序
Arrays.sort(people, (second, first) -> Integer.compare(first.length(), second.length()));
2、數組統計某元素個數
long num = Arrays.stream(name).filter(x -> x.equals("tiger")).count();
3、數組去重過濾並轉化成集合
List<String> filterList = Arrays.stream(name).filter(x -> !x.equals("趙強")).collect(Collectors.toList());
4、數組過濾,並對元素加後綴
List<String> filterList = Arrays.stream(name).filter(x -> !x.equals("tiger")).map(y -> y.concat(".jpg")).collect(Collectors.toList());
5、數組統計求和
int num = Arrays.stream(arr).reduce(0, Integer::sum);
double sum = Arrays.asList(10.0, 20.0, 30.0).stream().map(x -> x + x * 0.05).reduce(Double::sum).get();
double sum = Stream.of(10.0, 20.0, 30.0).map(x -> x + x * 0.05).reduce(Double::sum).get();
int sum = Stream.of(1, 2, 3, 4, 5).map(x -> x + x * 5).reduce(Integer::sum).get();
====== 求和 ======
BinaryOperator<Integer> add = Integer::sum;
Integer x = add.apply(20, 30);
====== 線程 ======
private static void lambdaRunnable() {
int age = 20;
Runnable r2 = () -> {
System.out.println(age);
System.out.println("Hello world two!"+age);
};
r2.run();
}