测试java的Lambda语法

import org.junit.Test;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.IntSummaryStatistics;
import java.util.List;
import java.util.function.Consumer;
import java.util.function.Predicate;
import java.util.function.Supplier;
import java.util.stream.Collectors;

public class LambdaTest {

    @Test
    public void test1() {
        // 用匿名内部类的方式来创建线程
        new Thread(new Runnable() {
            @Override
            public void run() {
                System.out.println("用匿名内部类的方式来创建线程！");
            }
        }).start();

        // 使用Lambda来创建线程
        new Thread(() -> System.out.println("使用Lambda来创建线程！")).start();
        Runnable runnable = () -> System.out.println("Lambda语法实现runnable");
        new Thread(runnable).start();

        List<String> items = new ArrayList<>();
        items.add("A");
        items.add("B");
        items.add("C");
        items.add("D");
        items.add("E");

        //lambda
        //Output : A,B,C,D,E
        items.forEach(item->System.out.println(item));

    }

    @Test
    public void test2(){
        // Consumer 一个入参，无返回值
        Consumer<String> consumer = s -> System.out.println(s);
        consumer.accept("Lambda语法Consumer案例！");

        Consumer<String> consumer1 = System.out::println;
        consumer.accept("Lambda语法Consumer案例2！");

        // Supplier 无入参，有返回值
        Supplier<String> supplier = () -> "Lambda语法Supplier案例！";
        String s = supplier.get();
        System.out.println(s);

        //Supplier<Category> categorySupplier = Category::new;
        //System.out.println(categorySupplier);
    }

    @Test
    public void test3(){
        //lambda表达式和函数式接口Predicate
        List<String> languages = Arrays.asList("Java", "Scala", "C++", "Haskell", "Lisp");

        System.out.println("Languages which starts with J :");
        //调用自己方法filter 第一个参数为集合，第二个过滤条件
        filter(languages, (str) -> ((String)str).startsWith("J"));

        System.out.println("Languages which ends with a ");
        filter(languages, (str) -> ((String)str).endsWith("a"));

        System.out.println("Print all languages :");
        filter(languages, (str) -> true);

        System.out.println("Print no language : ");
        filter(languages, (str) -> false);

        System.out.println("streamFilter Test : ");
        testFilter(languages);

        //map
    }
    public static void filter(List<String> names, Predicate condition) {
       /* names.forEach(s -> {
            if (condition.test(s)){
                System.out.println(s);
            }
        });*/
        //filter()方法是获得一个新的列表，且其每个元素符合过滤原则
        names.stream().filter(condition).forEach(System.out::println);

    }

    //lambda表达式中加入Predicate
    public static void testFilter(List<String> names){
        Predicate<String> startsWithJ = (n) -> n.startsWith("J");
        Predicate<String> fourLetterLong = (n) -> n.length() == 4;
        names.stream()
                .filter(startsWithJ.and(fourLetterLong)) //filter 验证是否符合该过滤条件 and or ..
                .forEach((n) -> System.out.print("nName, which starts with 'J' and four letter long is : " + n));
    }

    @Test
    public void strTest(){
        List<String> strList = Arrays.asList("abc", "bcd", "defg", "jk");
        // 创建一个字符串列表，每个字符串长度大于2 filter()生成一个新的集合
        List<String> filtered = strList.stream().filter(x -> x.length()> 2).collect(Collectors.toList());
        System.out.printf("Original List : %s, filtered list : %s %n", strList, filtered);
    }

    @Test
    public void mapTest(){
        //使用lambda表达式的Map和Reduce示例
        List<Integer> costBeforeTax = Arrays.asList(100, 200, 300, 400, 500);
        //map替换array值并遍历
        costBeforeTax.stream().map((cost) -> cost + .12*cost).forEach(System.out::println);

        //使用lambda表达式的Map示例 map替换值之后 reduce计算list的总和
        double bill = costBeforeTax.stream().map((cost) -> cost + .12*cost)
                .reduce((sum, cost) -> sum + cost).get();
        System.out.println("总和："+bill);
    }

    //流的distinct()方法去重
    @Test
    public void distinctTest(){
        // 用所有不同的数字创建一个正方形列表
        List<Integer> numbers = Arrays.asList(9, 10, 3, 4, 7, 3, 4);
        List<Integer> distinct = numbers.stream().distinct().collect(Collectors.toList());
        System.out.printf("Original List : %s,  Square Without duplicates : %s %n", numbers, distinct);
    }

    //集合操作
    @Test
    public void operateTest(){
        //获取数字的个数、最小值、最大值、总和以及平均值
        List<Integer> primes = Arrays.asList(2, 3, 5, 7, 11, 13, 17, 19, 23, 29);
        IntSummaryStatistics stats = primes.stream().mapToInt((x) -> x).summaryStatistics();
        System.out.println("Highest prime number in List : " + stats.getMax());
        System.out.println("Lowest prime number in List : " + stats.getMin());
        System.out.println("Sum of all prime numbers : " + stats.getSum());
        System.out.println("Average of all prime numbers : " + stats.getAverage());

    }

}