java 8 複合Lambda 表達式

comparator  比較器複合

//排序

Comparator.comparing(Apple::getWeight);
List<Apple> list = Stream.of(new Apple(1, "a"), new Apple(2, "b"), new Apple(3, "c"))
        .collect(Collectors.toList());

list.sort(Comparator.comparing(Apple::getWeight));  //按重量排序

list.stream()
        .sorted(Comparator.comparing(Apple::getName))
        .collect(Collectors.toList());

//先按重量倒序,若是重量同樣,再按名稱排序
list.sort(Comparator.comparing(Apple::getWeight)
        .reversed()
        .thenComparing(Apple::getName));

 

Predicate 謂詞 複合

//判斷是蘋果b
Predicate<Apple> isBApple = apple -> Objects.equals("b", apple.getName());

isBApple.negate();      //不是蘋果b


//不是蘋果b,而且蘋果重量大於1  -->  apple.name != "b" && apple.weight > 1
isBApple.negate().and(apple -> apple.getWeight() > 1);

// ((apple.name != "b") && apple.weight > 1)  or apple.weight==0
isBApple.negate()
        .and(apple -> apple.getWeight() > 1)
        .or(apple -> apple.getWeight()==0);

Function 函數複合

//f(x) = x+1
Function<Integer, Integer> f = x -> x + 1;
//g(x) = x*2
Function<Integer, Integer> g = x -> x * 2;
// g(f(x))
Function<Integer, Integer> h = f.andThen(g);
// f(g(x))
Function<Integer, Integer> z = f.compose(g);