函数式编程 - 方法引用

方法引用有助于通过方法名称指向方法。方法引用使用"::"符号描述。方法引用可用于指向以下类型的方法 −

• 静态方法 - 可以使用 ClassName::Method 名称表示法引用静态方法。

//方法引用 - 静态方式
Factory vehicle_factory_static = VehicleFactory::prepareVehicleInStaticMode;

• 实例方法 - 可以使用 Object::Method 名称表示法引用实例方法。

//方法引用 - 实例方式
Factory vehicle_factory_instance = new VehicleFactory()::prepareVehicle;

以下示例展示了方法引用在 Java 8 及更高版本中的工作方式。

interface Factory {
   Vehicle prepare(String make, String model, int year);
}

class Vehicle {
   private String make;
   private String model;
   private int year;

   Vehicle(String make, String model, int year){
      this.make = make;
      this.model = model;
      this.year = year;
   }

   public String toString(){
      return "Vehicle[" + make +", " + model + ", " + year+ "]";
   }    
}

class VehicleFactory {
   static Vehicle prepareVehicleInStaticMode(String make, String model, int year){
      return new Vehicle(make, model, year);
   }

   Vehicle prepareVehicle(String make, String model, int year){
      return new Vehicle(make, model, year);
   }
}

public class FunctionTester {    
   public static void main(String[] args) {               
      //Method Reference - Static way
      Factory vehicle_factory_static = VehicleFactory::prepareVehicleInStaticMode;        
      Vehicle carHyundai = vehicle_factory_static.prepare("Hyundai", "Verna", 2018);
      System.out.println(carHyundai);

      //Method Reference - Instance way
      Factory vehicle_factory_instance = new VehicleFactory()::prepareVehicle;        
      Vehicle carTata = vehicle_factory_instance.prepare("Tata", "Harrier", 2019);
      System.out.println(carTata); 
   } 
}

输出

Vehicle[Hyundai, Verna, 2018]
Vehicle[Tata, Harrier, 2019]