Java Lambda 表達式的幾各形式

一、Lambda表達式的組成主要有傳入參數列表（參數1，參數2，...），箭頭 ->，及返回值，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表達式時：

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();

}
}</pre> 






加入了Lambda表達式后可以寫成（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();
}

}</pre> 






看完后是不是很激動。 



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));

}
}</pre> 






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));

}
}</pre> 






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));

} 
}</pre> 






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));

}


}</pre> 






在jkd8中Java加入了激動人心的函數式編程方法Lambda表達式，這使得代碼更加簡潔。