Java --lambda 表达式

使用

(params) -> expression
(params) -> statement
(params) -> { statements }

注意：
1.lambda表达式有个限制，那就是只能引用 final 或 final 局部变量，这就是说不能在lambda内部修改定义在域外的变量。

List<Integer> primes = Arrays.asList(new Integer[]{2, 3,5,7});
int factor = 2;
primes.forEach(element -> { factor++; }); 

Compile time error : "local variables referenced from a lambda expression must be final or effectively final"

1.列表操作

1.简单循环列表

//初始化数据
   List<Books> books=Arrays.asList(new Books("西游记",15),new Books("java",20),
        new Books("金瓶梅",10),new Books("水湖庄",30));
  //循环书名
 books.forEach(books1 -> System.out.println("书名:"+books1.getName()+" 价格:"+books1.getPrice()));

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2.过滤数据

//过滤价格
 List<Books> highPrice=books.stream().filter(books1 -> books1.getPrice()>15).collect(Collectors.toList());

 highPrice.forEach(highbook-> System.out.println("价格高于15的书："+highbook.getName()));

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3.排序

 System.out.println("从低到高排序");
List<Books> sortBooks=books.stream().sorted(Comparator.comparing(Books::getPrice)).collect(Collectors.toList());

sortBooks.forEach(book-> System.out.printf("书名：%s,价格:%s\n",book.getName(),book.getPrice()));

System.out.println("从高到低排序");
 List<Books> sortBooks2=books.stream().sorted(Comparator.comparing(Books::getPrice).reversed()).collect(Collectors.toList());
sortBooks2.forEach(book-> System.out.printf("书名：%s,价格:%s\n",book.getName(),book.getPrice()));

image.png

4.书本价格相加

 int totalPrice=books.stream().map(Books::getPrice).reduce(0,(a,b)->a+b);
System.out.println(totalPrice);

5.去重

 //使用distinct 方法去重
List<Integer> numbers = Arrays.asList(9, 10, 3, 4, 7, 3, 4);
List<Integer> distinct = numbers.stream().map( i -> i*i).distinct().collect(Collectors.toList());
System.out.printf("Original List : %s,  Square Without duplicates : %s %n", numbers, distinct);

image.png

替代内部类

  //替代内部类
    public void test2(){
        new Thread(new Runnable() {
            @Override
            public void run() {
                System.out.println("Before Java8, too much code for too little to do");
            }
        }).start();

        new Thread( () -> System.out.println("In Java8, Lambda expression rocks !!") ).start();
    }

简单的用可以，如果链条太长的话，有时候会让代码反而更加难看懂