Java Lambda 表达式的几各形式

一、Lambda表达式的组成主要有传入参数列表（参数1，参数2，...），箭头 ->，及返回值，可以是某个值，或者结构体。

如下举一个小小的例子：

在没有使用Lambda表达式时：

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表达式后可以写成（下面以3种方法实现）：

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();
    }
}

看完后是不是很激动。

下面再放几个例子，参才其实现方式：

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));
    }

}