java8學習

package com.cyh.java8;

import org.junit.Assert;
import org.junit.BeforeClass;
import org.junit.Test;

import java.util.*;
import java.util.stream.IntStream;
import java.util.stream.Stream;

public class Demo {

	private static List<Integer> list = new ArrayList<>(5);

	@BeforeClass
	public static void init(){
		for (int i = 0; i < 5; i++) {
			list.add(i);
		}
	}
	/**
	 * filter和findAny方法連用獲取集合中匹配的值
	 *
	 */
	@Test
	public void findAny(){
		Optional<Integer> any = list.stream().filter(x -> x.intValue() == 4).findAny();
		Assert.assertTrue(any.isPresent());
		if (any.isPresent()){
			System.out.println(any.get());
		}
	}
	/**
	 * anyMatch 方法測試
	 * 其中至少一個知足條件
	 */
	@Test
	public void anyMatch(){
		Assert.assertTrue(list.stream().anyMatch(x->x.intValue()<2));
	}
	/**
	 * anyMatch 方法測試
	 * 所有知足條件
	 */
	@Test
	public void allMatch(){
		Assert.assertTrue(list.stream().allMatch(x->x.intValue()<5));
	}
	/**
	 * noneMatch 方法測試
	 * 所有都不知足條件
	 */
	@Test
	public void noneMatch(){
		Assert.assertTrue(list.stream().noneMatch(x->x.intValue()>5));
	}
	/**
	 * noneMatch 方法測試
	 * 所有都不知足條件
	 */
	@Test
	public void optionalInt(){
		//將封裝類型轉化爲基本類型
		IntStream intStream = list.stream().mapToInt(x->x);
		int[] ints = intStream.toArray();
		//批量轉型
		long[] longs = list.stream().mapToInt(x -> x).asLongStream().toArray();
		double[] doubles = list.stream().mapToInt(x -> x).asDoubleStream().toArray();
		System.out.println(Arrays.toString(ints));
		System.out.println(Arrays.toString(longs));
		System.out.println(Arrays.toString(doubles));
		//將基礎類型劉轉化爲封裝類型流
		Stream<Integer> boxed = list.stream().mapToInt(x -> x).boxed();
		Integer[] integers = boxed.toArray(Integer[]::new);
		System.out.println(Arrays.toString(integers));
		//OptionalInt 基礎類型option		OptionalInt
		OptionalInt any = list.stream().mapToInt(x -> x).findAny();
		System.out.println(any.isPresent());

		List<Integer> lst = new ArrayList<>();
		OptionalInt any1 = lst.stream().mapToInt(x -> x).findAny();
		System.out.println(any1.isPresent());
		/**
		 *     private static final OptionalInt EMPTY = new OptionalInt();
		 *
		 *     private final boolean isPresent;
		 *     private final int value;
		 *
		 *     private OptionalInt() {
		 *         this.isPresent = false;
		 *         this.value = 0;
		 *     }
		 *
		 *     public static OptionalInt empty() {
		 *         return EMPTY;
		 *     }
		 *
		 *     private OptionalInt(int value) {
		 *         this.isPresent = true;
		 *         this.value = value;
		 *     }
		 *
		 *
		 *     public static OptionalInt of(int value) {
		 *         return new OptionalInt(value);
		 *     }
		 *
		 *     能夠看出OptionalInt並非判斷是否爲0；使用of獲取的對象均爲true
		 */
	}

}