我正在探索scala和Java 1.8，但无法在Java 1.8 Lambda表达式中找到等效的代码。
Scala代码：
object Ex1 extends App {
def single(x:Int):Int =x
def square(x:Int):Int = x * x
def cube(x:Int):Int = x*x*x
def sum(f:Int=>Int,a:Int,b:Int):Int=if (a>b) 0 else f(a) + sum(f,a+1,b)
def sumOfIntegers(a:Int,b:Int)=sum(single,a,b)
def sumOfSquares(a:Int,b:Int)=sum(square,a,b);
def sumOfCubes(a:Int,b:Int)=sum(cube,a,b);
println(sumOfIntegers(1,4));
println(sumOfSquares(1,4));
println(sumOfCubes(1,4));
}
output:
10
30
100
Java的
public class Test1{
public int single(int x){
return x;
}
public int square(int x){
return x * x;
}
public int cube(int x){
return x * x * x;
}
// what's next? How to implement sum() method as shown in Scala?
// Stuck in definition of this method, Stirng s should be function type.
public int sum( Sring s , int a, int b){
// what will go here?
}
public int sumOfIntegers(int a, int b){
return sum("single<Function> how to pass?",a,b);
}
public int sumOfSquares(int a, int b){
return sum("square<Function> how to pass?",a,b);
}
public int sumOfCubes(int a, int b){
return sum("cube<Function> how to pass?",a.b);
}
}
使用JDK 1.8是否可以实现相同的目的？
最佳答案
您将需要定义将要使用的方法。 Java随附的唯一一个是Function<X,Y>，它（与Integer一起使用）可用于single，square和cube，而BiFunction<T,Y, R>可以用于三个sumOf。
interface Sum {
Integer apply(Function<Integer, Integer> func, int start, int end);
}
单个，正方形和多维数据集可以是类中的方法（请参见
cube或内联（请参见其他两个）。它们是Fuction s。然后可以将此函数传递给其他方法，并使用variableName.apply进行调用。 class Test
{
private static Integer sum(Function<Integer, Integer> func, int a, int b) {
if (a>b)
return 0;
else return func.apply(a) + sum(func,a+1,b);
}
private static Integer cube(Integer a) {
return a * a * a;
}
public static void main (String[] args) throws java.lang.Exception
{
Function<Integer,Integer> single = a -> a;
Function<Integer,Integer> square = a -> a * a;
Function<Integer,Integer> cube = Test::cube;
// You can not do the sum in-line without pain due to its recursive nature.
Sum sum = Test::sum;
BiFunction<Integer, Integer, Integer> sumOfIntegers = (a, b) -> sum.apply(single, a, b);
BiFunction<Integer, Integer, Integer> sumOfSquares = (a, b) -> sum(square, a, b); // You could just use the static method directly.
BiFunction<Integer, Integer, Integer> sumOfCubes = (a, b) -> sum(cube, a, b);
System.out.println(sumOfIntegers.apply(1,4));
System.out.println(sumOfSquares.apply(1,4));
System.out.println(sumOfCubes.apply(1,4));
}
}