Java8新特性 - Lambda表达式 - Functional Interfaces

Mapper.java

package corejava8.lambda;

@FunctionalInterface
public interface Mapper<T> {
	// An abstract method
	int map(T source);

	// A generic static method
	public static <U> int[] mapToInt(U[] list, Mapper<? super U> mapper) {
		int[] mappedValues = new int[list.length];
		for (int i = 0; i < list.length; i++) {
			// Map the object to an int
			mappedValues[i] = mapper.map(list[i]);
		}
		return mappedValues;
	}
}

MapperTest.java

package corejava8.lambda;

public class MapperTest {
	public static void main(String[] args) {
		// Map names using their length
		System.out.println("Mapping names to their lengths:");
		String[] names = { "David", "Li", "Doug" };
		int[] lengthMapping = Mapper.mapToInt(names,
				(String name) -> name.length());
		printMapping(names, lengthMapping);
		System.out.println("\nMapping integers to their squares:");
		Integer[] numbers = { 7, 3, 67 };
		int[] countMapping = Mapper.mapToInt(numbers, (Integer n) -> n * n);
		printMapping(numbers, countMapping);
	}

	public static void printMapping(Object[] from, int[] to) {
		for (int i = 0; i < from.length; i++) {
			System.out.println(from[i] + " mapped to " + to[i]);
		}
	}
}

运行结果:
Mapping names to their lengths:
David mapped to 5
Li mapped to 2
Doug mapped to 4

Mapping integers to their squares:
7 mapped to 49
3 mapped to 9
67 mapped to 4489