JUC-11. 四种函数式接口_java 11函数式编程自带的函数式接口

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11. 四种函数式接口

• 在Java8支持Lambda表达式以后，为了满足Lambda表达式的一些典型使用场景，JDK为我们提供了大量常用的函数式接口。它们主要在java.util.function包中。

• 可以大致分为四种类型：

  

  • Function：功能型函数接口

  • Predicate：断言型接口

  • Suppier：供给型接口

  • Consumer：消费型接口

1. Function接口

• Function接口是对实例进行处理转换的接口，定义了一个名叫apply()的抽象方法，传入一个泛型T对象，并返回一个泛型R对象

  

• 案例

  public class FunctionTest {
      public static void main(String[] args) {
          //传入一个数字，返回平方
          Function<Integer, Integer> function = (num) -> {
              return num * num;
          };
          System.out.println(function.apply(10));//100
      }
  }
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• 与Function相关的接口

  接口名称	方法名称	方法前面
  Function	apply	(T) => R
  BiFunction	apply	(T, U) => R
  DoubleFunction	apply	(double) => R
  DoubleToIntFunction	applyAsInt	(double) => int
  DoubleToLongFunction	applyAsLong	(double) => long
  IntFunction	apply	(int) => R
  IntToDoubleFunction	applyAsDouble	(int) => double
  IntToLongFunction	applyAsLong	(int) => long
  LongFunction	apply	(long) => R
  LongToDoubleFunction	applyAsDouble	(long) => double
  LongToIntFunction	applyAsInt	(long) => int
  ToDoubleFunction	applyAsDouble	(T) => double
  ToDoubleBiFunction	applyAsDouble	(T, U) => double
  ToIntFunction	applyAsInt	(T) => int
  ToIntBiFunction	applyAsInt	(T, U) => int
  ToLongFunction	applyAsLong	(T) => long
  ToLongBiFunction	applyAsLong	(T, U) => long

2. Predicate接口

• Predicate接口是判断是与否的接口，定义了一个名叫test的抽象方法，传入一个泛型T对象，并返回一个boolean类型

  

• 案例

  public class PredicateTest {
      public static void main(String[] args) {
          Predicate predicate = (Object str)->{
              return "a".equals(str);
          };
  
          System.out.println(predicate.test("a"));//true
          System.out.println(predicate.test("A"));//false
      }
  }
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• 与Predicate相关的接口

  接口名称	方法名称	方法签名
  Predicate	test	(T) => boolean
  BiPredicate	test	(T, U) => boolean
  DoublePredicate	test	(double) => boolean
  IntPredicate	test	(int) => boolean
  LongPredicate	test	(long) => boolean

3. Supplier接口

• Supplier接口是对象实例的提供者，定义了一个名叫get的抽象方法，它不用传入参数，并返回一个泛型T对象

  

• 案例

  public class FunctionInterfaceTest {
      public static void main(String[] args) {
          Supplier<Car> supplier = ()->{
              return new Car("奔驰",1000);
          };
          //用supplier的get方法创建car对象
          Car car = supplier.get();
          System.out.println(car.getName() + "的价钱为：" + car.getPrice());
      }
  }
  
  //一个汽车类，有两个属性：车名和价钱
  class Car{
      private String name;
      private Integer price;
  
      public Car(String name, Integer price) {
          this.name = name;
          this.price = price;
      }
  
      public String getName() {
          return name;
      }
  
      public void setName(String name) {
          this.name = name;
      }
  
      public Integer getPrice() {
          return price;
      }
  
      public void setPrice(Integer price) {
          this.price = price;
      }
  }
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• 与Supplier相关的接口

  接口名称	方法名称	方法签名
  Supplier	get	() => T
  BooleanSupplier	getAsBoolean	() => boolean
  DoubleSupplier	getAsDouble	() => double
  IntSupplier	getAsInt	() => int
  LongSupplier	getAsLong	() => long

4. Consumer接口

• Consumer接口是一个类似消费者的接口，定义了一个名叫accept的抽象方法，传入一个泛型T对象，没有返回值

  

• 案例

  public class FunctionInterfaceTest {
  
      public static void main(String[] args) {
          Supplier<Car> supplier = ()->{
              return new Car("奔驰",1000);
          };
          Consumer<Car> consumer = (Car car)->{
              System.out.println(car.getName() + "的价钱为：" + car.getPrice());
          };
          consumer.accept(supplier.get());
      }
  }
  
  //一个汽车类，有两个属性：车名和价钱
  class Car{
      private String name;
      private Integer price;
  
      public Car(String name, Integer price) {
          this.name = name;
          this.price = price;
      }
  
      public String getName() {
          return name;
      }
  
      public void setName(String name) {
          this.name = name;
      }
  
      public Integer getPrice() {
          return price;
      }
  
      public void setPrice(Integer price) {
          this.price = price;
      }
  }
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• 与Consumer相关的接口

  接口名称	方法名称	方法签名
  Consumer	accept	(T) => void
  DoubleConsumer	accept	(double) => void
  IntConsumer	accept	(int) => void
  LongConsumer	accept	(long) => void
  ObjDoubleConsumer	accept	(T, double) => void
  ObjIntConsumer	accept	(T, int) => void
  ObjLongConsumer	accept	(T, long) => void