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Java8 常用函数式接口及例子

Java8Testpackage com.smile.zhou;

import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.Test;

import java.util.Arrays;
import java.util.Comparator;
import java.util.List;
import java.util.function.IntBinaryOperator;
import java.util.function.Supplier;
import java.util.stream.Collectors;

public class Java8Test {
	@Test
	void testPredicate() {
		List<Character> characters = Arrays.asList('A', 'b', 'C', 'd', 'E', 'f');
		Assertions.assertTrue(characters.stream().filter(Character::isUpperCase).collect(Collectors.toSet()).containsAll(Arrays.asList('A', 'C', 'E')));
		Assertions.assertTrue(characters.stream().filter(Character::isLowerCase).collect(Collectors.toSet()).containsAll(Arrays.asList('b', 'd', 'f')));
	}

	@Test
	void testSupplier() {
		class X {
		}
		Supplier<X> supplier = () -> new X();
		X x1 = supplier.get();
		X x2 = supplier.get();
		System.out.println(x1);
		System.out.println(x2);
	}

	@Test
	void testConsumer() {
		List<Character> characters = Arrays.asList('A', 'b', 'C', 'd', 'E', 'f');
		characters.forEach(System.out::println);
	}

	@Test
	void testBinaryOperator() {
		IntBinaryOperator add = (x, y) -> x + y;
		IntBinaryOperator sub = (x, y) -> x - y;
		calc("+", add);
		calc("-", sub);
		calc("*", (int x, int y) -> x * y);
		calc("/", (int x, int y) -> x / y);
	}

	private void calc(String op, IntBinaryOperator operator) {
		int a = 2, b = 1;
		System.out.println(String.format("%d %s %d = %d", a, op, b, operator.applyAsInt(a, b)));
	}

	@Test
	void testComparator() {
		List<Character> characters = Arrays.asList('A', 'b', 'C', 'd', 'E', 'f');
		System.out.println("顺序：" + Arrays.toString(characters.stream().sorted().toArray()));
		System.out.println("逆序：" + Arrays.toString(characters.stream().sorted(Comparator.reverseOrder()).toArray()));
	}

}

这里只是简单的做个笔记，方便以后查阅。