Java Lambda 運算式的幾各形式

標籤：

一、Lambda運算式的組成主要有傳入參數列表（參數1，參數2，...），箭頭 ->，及傳回值，可以是某個值，或者結構體。

如下舉一個小小的例子：

在沒有使用Lambda運算式時：

import java.util.stream.Stream;/** * * @author Kangjun */public class Demo {    public static void  main(String[] args){        Dog dog1 = new Dog("dog1",2);        Dog dog2 = new Dog("dog2",1);        Dog dog3 = new Dog("dog3",3);                Dog[] dogs = {dog1,dog2,dog3};        printDogs(dogs);                Arrays.sort(dogs, new Comparator<Dog>(){            @Override            public int compare(Dog t, Dog t1) {                return t.getWeight()-t1.getWeight();            }                    });               printDogs(dogs);            }        public static void printDogs(Dog[] dogs){        for(Dog d : dogs){            System.out.println(d);        }        System.out.println();    }}

加入了Lambda運算式後可以寫成（下面以3種方法實現）：

import java.util.stream.Stream;/** * * @author Kangjun */public class Demo {    public static void  main(String[] args){        Dog dog1 = new Dog("dog1",2);        Dog dog2 = new Dog("dog2",1);        Dog dog3 = new Dog("dog3",3);                Dog[] dogs = {dog1,dog2,dog3};        printDogs(dogs);               // Arrays.sort(dogs,(m,n)->m.getWeight()-n.getWeight()); //Lambda方法一        //Arrays.sort(dogs,(Dog m,Dog n)->Integer.compare(m.getWeight(), n.getWeight()));//Lambda方法二        //printDogs(dogs);                //方法三        Stream<Dog> dogStream = Stream.of(dogs);        Stream<Dog> sortedDogStream = dogStream.sorted((Dog m, Dog n) -> Integer.compare(m.getWeight(), n.getWeight()));        sortedDogStream.forEach(d -> System.out.print(d));            }        public static void printDogs(Dog[] dogs){        for(Dog d : dogs){            System.out.println(d);        }        System.out.println();    }}

看完後是不是很激動。

下面再放幾個例子，參才其實現方式：

import java.util.Arrays;/** * * @author Kangjun */public class StandardSyntaxLambda {   private static final String[] arr = {"program", "creek", "is", "a", "java", "site"};        public static void main(String[] args){        Arrays.sort(arr, (String a,String b) -> Integer.compare(a.length(), b.length()) );        System.out.println(Arrays.toString(arr));    }}

import java.util.Arrays;/** * * @author Kangjun */public class ParameterTypeInferredLambda {    private static final String[] arr = {"program", "creek", "is", "a", "java", "site"};        public static void main(String[] args){        Arrays.sort(arr,(m,n) -> Integer.compare(m.length(), n.length()));        System.out.println(Arrays.toString(arr));    }}

import java.util.Arrays;/** * * @author Kangjun */public class MultipleLinesCodeLambda {    private static final String[] arr = {"program", "creek", "is", "a", "java", "site"};        public static void main(String[] args){        Arrays.sort(arr,(String m,String n) -> {            return m.length() - n.length();        });                System.out.println(Arrays.toString(arr));    } }

import java.util.stream.Stream;/** * * @author Kangjun */public class SingleParameterInferredTypeLambda {    private static final String[] arr = {"program", "creek", "is", "a", "java", "site"};    public static void main(String[] args) {        Stream<String> arrStream = Stream.of(arr);        Stream<String> sortedStream = arrStream.sorted((a, b) -> a.length() - b.length());        sortedStream.forEach(x -> System.out.println(x));    }}

Java Lambda 運算式的幾各形式