如何在Java中使用Lambda表达式实现ToDoubleFunction ？
ToDoubleFunction<T>是java.util.function包中定义的功能接口 。该功能接口期望参数作为输入并产生双值结果。它用作lambda表达式 或方法 引用的分配目标。ToDoubleFunction<T> 接口仅包含一种抽象方法applyAsDouble()。
语法
@FunctionalInterface
public interface ToDoubleFunction<T> {
double applyAsDouble(T value);
}示例1
import java.util.function.ToDoubleFunction;
public class ToDoubleFunctionTest1 {
public static void main(String args[]) {
ToDoubleFunction<String> strLength = s -> s.length(); // lambda expression System.out.println("The length of a given String using lambda expression is: " + strLength.applyAsDouble("nhooo"));
ToDoubleFunction<String> innerClassImplementation = new ToDoubleFunction<String>() {
@Override // anonymous inner class public double applyAsDouble(String value) {
return value.length();
}
};
System.out.println("The length of a given string using anonymous inner class is: " + innerClassImplementation.applyAsDouble("Tutorix"));
}
}输出结果
The length of a given String using lambda expression is: 14.0 The length of a given string using anonymous inner class is: 7.0
示例2
import java.util.*;
import java.util.stream.*;
import java.util.function.ToDoubleFunction;
public class ToDoubleFunctionTest2 {
public static void main(String[] args) {
List<String> marksList = new ArrayList<String>();
marksList.add("98");
marksList.add("95");
marksList.add("90");
marksList.add("75");
marksList.add("70");
ToDoubleFunction<String> function = (String score) -> Double.valueOf(score); // lambda marksList.stream()
.mapToDouble(function)
.forEach(System.out::println); // method reference }
}输出结果
98.0 95.0 90.0 75.0 70.0
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