Jdk8 高阶函数的简单使用：map，reduce，filter，sorted

柔光的暖阳◎ 2022-04-17 05:17 323阅读 0赞

转载地址：[https://blog.csdn.net/rongrong\_love\_lc/article/details/72845528][https_blog.csdn.net_rongrong_love_lc_article_details_72845528]

备份下：

package test;
    
    
    import java.util.ArrayList;
    import java.util.IntSummaryStatistics;
    import java.util.stream.Collectors;
    
    import org.junit.Test;
    
    public class LambdaTest {
    
    	static ArrayList<Integer> a = new ArrayList<Integer>();
    	static ArrayList<Integer> b = null;
    	static {
    		a.add(4);
    		a.add(3);
    		a.add(2);
    		a.add(1);
    		a.add(6);
    		a.add(7);
    		a.add(8);
    		a.add(5);
    		a.add(9);
    		a.add(0);
    	}
    
    	@Test
    	public void testMap_forEach() {
    		System.out.println("mmmmmmmmmmmmmmmmmmmmmmmmmmm");
    		a.stream().map((x) -> (x + 100)).forEach((num) -> {
    			System.out.print(num + ",");
    		});
    		a.forEach(System.out::print);
    		System.out.println();
    	}
    
    	@Test
    	public void testMap_collect() {
    		System.out.println("mmmmmmmmmmmmmmmmmmmmmmmmmmm1111");
    		b = (ArrayList<Integer>) a.stream().map((x) -> (x + 100)).collect(Collectors.toList());
    		a.forEach(System.out::print);
    		System.out.println();
    		b.forEach(System.out::print);
    	}
    
    	@Test
    	public void testReduce() {
    		System.out.println("rrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr");
    		int b = a.stream().reduce((x, y) -> x + y).get();
    		a.stream().forEach(System.out::print);
    		System.out.println();
    		System.out.println("sum = " + b);
    	}
    
    	@Test
    	public void testFilter() {
    		System.out.println("ffffffffffffffffffffffff");
    		b = (ArrayList<Integer>) a.stream().filter((y) -> y % 2 != 0).collect(Collectors.toList());
    		
    		b.forEach((x) -> System.out.print(x + ","));
    		System.out.println();
    	}
    
    	@Test
    	public void testSort() {
    		System.out.println("ssssssssssssssssssssssssssss");
    		b = (ArrayList<Integer>) a.stream().sorted().collect(Collectors.toList());
    		b.forEach((x) -> System.out.print(x + ","));
    		System.out.println();
    	}
    
    	@Test
    	public void testSort1() {
    		System.out.println("ssssssssssssssssssssssssssss11111111");
    		b = (ArrayList<Integer>) a.stream().sorted((x, y) -> {
    			if (x > y) {
    				return -1;
    			} else if (x == y) {
    				return 0;
    			} else {
    				return 1;
    			}
    		}).collect(Collectors.toList());
    		b.forEach((x) -> System.out.print(x + ","));
    		System.out.println();
    	}
    
    	@Test
    	public void testSort2() {
    		System.out.println("ssssssssssssssssssssssssssss2222222222222222");
    		b = (ArrayList<Integer>) a.stream().sorted((x, y) -> (x.compareTo(y))).collect(Collectors.toList());
    		b.forEach((x) -> System.out.print(x + ","));
    		System.out.println();
    	}
    
    	@Test
    	public void testSort3() {
    		System.out.println("ssssssssssssssssssssssssssss3333333333333333333");
    		b = (ArrayList<Integer>) a.stream().sorted((x, y) -> (-x.compareTo(y))).collect(Collectors.toList());
    		b.forEach((x) -> System.out.print(x + ","));
    		System.out.println();
    	}
    
    	@Test
    	public void testSummaryStatistics() {
    		System.out.println("================SummaryStatistics====================");
    		IntSummaryStatistics statistics = a.stream().mapToInt((x) -> x).summaryStatistics();
    		System.out.println("最大值:" + statistics.getMax());
    		System.out.println("最小值:" + statistics.getMin());
    		System.out.println("平均值:" + statistics.getAverage());
    		System.out.println("总数:" + statistics.getCount());
    		System.out.println("和:" + statistics.getSum());
    	}
    
    	@Test
    	public void testParallelStream() {
    		System.out.println("*******************ParallelStream**********************");
    		// 以下使用有错误
    		// IntStream intStream = a.parallelStream().mapToInt((x)->x);
    		// System.out.println("最大值:"+intStream.max());
    		// System.out.println("最小值:"+intStream.min());
    		// System.out.println("平均值:"+intStream.average());
    		// System.out.println("总数:"+intStream.count());
    		// System.out.println("和:"+intStream.sum());
    		System.out.println("最大值:" + a.parallelStream().mapToInt((x) -> x).max());
    		System.out.println("最小值:" + a.parallelStream().mapToInt((x) -> x).min());
    		System.out.println("平均值:" + a.parallelStream().mapToInt((x) -> x).average());
    		System.out.println("总数:" + a.parallelStream().mapToInt((x) -> x).count());
    		System.out.println("和:" + a.parallelStream().mapToInt((x) -> x).sum());
    	}
    
    }

[https_blog.csdn.net_rongrong_love_lc_article_details_72845528]: https://blog.csdn.net/rongrong_love_lc/article/details/72845528