lambda

案例

案例1

new Threaad(new Runable(){public void run(){System.out.println("xxx"):}
}).start();

new Thread(()->{System.out.println("xxx")；}
).star();

案例2

public static int calculateNum(IntBinaryOperator operator){int a = 10;int b = 200;return operator.applyAsInt(a,b);
}
public void main(String[] args){calculateNum( (a,b)-> a*b );
}

案例3

public static void printNum(Inpredicate predicate){int[] arr = {1,2,3,4,5,6,7,8,9,10};for(int i: arr){if(predicate.test(i)){System.out.println(i);}}
}public void main(String[] args){printNum(x->{return x%2==0;})
}

案例4

public static  R typeConver(Function function){String str = "12345";R result = function.apply(str);return result;
}public void main(String[] args){Integer result = typeConver(x->Integer.valueOf(x));
}

案例5

public static void foreachArr(IntConsumer consumer){int[] arr = {1,2,3,4,5,6,7,8};for(int i:arr){consumer.accept(i);}
} public void main(String[] args){foreachArr(x->System.out.println(x));
}

Stream

案例

• 数据准备

public class Author{private Long id;private String name;private Integer age;private String intro;private List books;
}public class Book{private Long id;private String name;private String category;private Integer score;private String intro;
}

private static List getAutors(){Author a1 = new Author(1l,"xx",22,"xxx",null);Author a2 = new Author(2l,"xx",33,"xxx",null);Author a3 = new Author(3l,"xx",44,"xxx",null);Author a4 = new Author(4l,"xx",55,"xxx",null);List b1 = new ArrayList<>();List b2 = new ArrayList<>();List b3 = new ArrayList<>();b1.add(new Book(1l,"xxxx","xxx",88,"xxxxxxxxx"));b1.add(new Book(2l,"xxxx","xxx",89,"xxxxxxxxx"));b1.add(new Book(3l,"xxxx","xxx",90,"xxxxxxxxx"));b2.add(new Book(4l,"xxxx","xxx",91,"xxxxxxxxx"));b2.add(new Book(5l,"xxxx","xxx",92,"xxxxxxxxx"));b2.add(new Book(6l,"xxxx","xxx",95,"xxxxxxxxx"));b3.add(new Book(7l,"xxxx","xxx",98,"xxxxxxxxx"));b3.add(new Book(8l,"xxxx","xxx",99,"xxxxxxxxx"));b3.add(new Book(9l,"xxxx","xxx",100,"xxxxxxxxx"));a1.setBooks(b1);a2.setBooks(b2);a3.setBooks(b3);a4.setBooks(b3);List authorList = new ArrayList<>(Arrays.asList(a1,a2,a3,a4));return authorList;}

创建流

// 年龄小于18 去重 打印
List authors = getAuthors();
authors.stream().distinct().filter(x->x.getAge()<18).forEach(x->System.out.println(x.getName()));// 数组创建
Integer[] arr = {1,2,3,4,5};
Arrays.stream(arr).distinct().forEach(x->System.out.println(x));
Stream.of(arr);
// Set
HashMap map=new HashMap<>();
Set> set=map.entrySet();
set.stream();
// Map
Map map = new HashMap();
map.entrySet().stream();

中间操作

// filter
// 打印姓名长度大于1
authors.stream().filter(x->x.getName().length()>1).forEach(x->System.out.println(x.getName()));// map
// 打印所有姓名
authors.stream().forEach(x->System.out.println(x.getName()));
authors.stream().map(x->x.getName()).forEach(x->System.out.println(x));// distinct
// 打印所有姓名 去重
authors.stream().distinct().map(x->x.getName()).forEach(x->System.out.println(x));// sorted
// 姓名去重 年龄排序
// implements Comparable
// public int compareTo(Author o){} 
authors.stream().distinct().sorted((a,b)->a.getAge()-b.getAge()).forEach(x->System.out.println(x.getAge() ));// limit
// 排序后限制2个
authors.stream().distinct().sorted((a,b)->a.getAge()-b.getAge()).limit(2).forEach(x->System.out.println(x.getName() ));// skip
// 排序 跳过1个
authors.stream().distinct().sorted((a,b)->b.getAge()-a.getAge()).skip(1).forEach(x->System.out.println(x.getName() ));// flatMap
authors.stream().flatMap(x->x.getBooks().stream()).distinct().forEach(x->System.out.println(x.getName() );

终结操作

// forEach
authors.stream().forEach(x->System.out.println(x.getName()));// count
authors.stream().flatMap(x->x.getBooks().stream()).distinct().count();// min max
authors.stream().distinct().flatMap(x->x.getBooks().stream()).map(x->x.getSocre()).max((a,b)->a-b).get();
authors.stream().distinct().flatMap(x->x.getBooks().stream()).map(x->x.getSocre()).min((a,b)->a-b).get();// collect
// list
authors.stream().map(x->x.getName()).collect(Collectors.toList());
// set
authors.stream().map(x->x.getName()).collect(Collectors.toSet());
// map
authors.stream().collect(Collectors.toMap(x->x.getName(),x->x.getBooks())) ;// anyMatch
authors.stream().anyMatch(x->x.getAge()>10);// allMatch
authors.stream().allMatch(x->x.getAge()>10);// noneMatch
authors.stream().noneMatch(x->x.getAge()>10);// findAny
// 随机获取
authors.stream().filter(x->x.getAge()>18).findAny();// findFirst
authors.stream().sorted((a,b)->a.getAge()-b.getAge()).findFirst();// reduce
// 求和
authors.stream().distinct().map(x->x.getAge()).reduce(0,(a,b)->a+b);
// 最大值
authors.stream().distinct().map(x->x.getAge()).reduce(0,(a,b)->a>b?a:b);
authors.stream().distinct().map(x->x.getAge()).reduce((a,b)->a>b?a:b);
// 最小值
authors.stream().distinct().map(x->x.getAge()).reduce(100,(a,b)->a>b?b:a);
authors.stream().distinct().map(x->x.getAge()).reduce((a,b)->a>b?b:a);

optional

创建

// 不确定author是否为空
Optional op = Optional.ofNullable(author);
// 确定object不为空
Optional.of(object);
// 返回空
Optional.empty()''

操作

// 如果存在
op.ifPresent(x->System.out.println(x.getName()));// 获取 
// 如果没有 创建默认值
op.orElseGet(()->new Author());
// 如果没有 抛出异常
op.orElseThrow(()->new Exception("xxx"));// 过滤
// 返回一个OPtional对象
op.fliter(x->x.getAge()>18);// 判断
op.isPresent();// 数据转换
op.map(x->x.getBooks()).ifPresent(x->System.out.println(x.size());

函数式接口

• 注解

  • @FunctionalInterface

• 接口

  • Consumer
    • void accept(T t)
    • BiConsumer
      • void accept(T t,U u)
  • Function
    • R apply(T t)
    • BiFunction
      • R accept(T t,U u)
  • Predicate
    • boolean test(T t)
    • BiPredicate
      • boolean accept(T t,U u)
  • Supplier
    • T get()
    • BooleanSupplier
      • boolean getAsBoolean()

• 默认方法

// Predicate and()
authors.stream().filter((x->x.getAge()>17).and(x->x.getName().length()>1)).forEach(x->System.out.println(x.getAge()));
// Predicate negate()
// 取反
// 取不大于17
authors.stream().filter((x->x.getAge()>17).negate()).forEach(x->System.out.println(x.getAge()));

方法引用

• 类名或对象名::方法名
  • 不会的话可以使用idea自动生成。。。

数据类型转换

// mapToInt
authors.stream().mapToInt(x->x.getAge()).fotEach(System.out::println);

并行流

// parallel() 开启并行流
// 或直接list.parallelStream()
// peek() 调试
Stream stream = Stream.of(1,2,3,4,5,6,7,8,9);
stream.parallel().peek(x->System.out.println(x+Thread.currentThread().getName())).filter(x->x>5).reduce((result,ele)->result+ele).get();