package common;

import org.hibernate.dialect.Ingres9Dialect;
import org.junit.Test;

import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class StreamDemo1 {
 @Test
 public void t1() {
 Stream<Integer> iterate = Stream.iterate(0, (x) -> x + 2);
 iterate.limit(10).forEach(System.out::println);
 }

 @Test
 public void t2() {
 ArrayList<Integer> list = new ArrayList<>();
 for (int i=0; i<20; i+=2) {
 list.add(i);
 }
 System.out.println(list);
 }

 @Test
 public void t3() {
 ArrayList<Integer> list = new ArrayList<>();
 for (int i=0; i<20; i+=2) {
 list.add(i);
 }
// list.forEach(v -> System.out.println(v));
 list.forEach(System.out::println);
 }

 public List<Integer> generate(int n) {
 Stream<Integer> generate = Stream.generate(() -> (int)(Math.random()*10));
 return generate.limit(n).collect(Collectors.toList());
 }

 @Test
 public void dis() {
 List<Integer> list = generate(10);
 System.out.println("before");
 System.out.println(list);
 List<Integer> list2 = list.stream().distinct().collect(Collectors.toList());
 System.out.println("distinct");
 System.out.println(list2);
 }

 @Test
 public void filter() {
 List<Integer> list = generate(10);
 System.out.println("before");
 System.out.println(list);
 List<Integer> list2 = list.stream()
 .filter(v -> v % 2 ==0)
 .distinct()
 .collect(Collectors.toList());
 System.out.println("distinct");
 System.out.println(list2);
 }

 @Test
 public void map() {
 List<Integer> list = generate(10);
 System.out.println("before");
 System.out.println(list);
 List<Double> list2 = list.stream()
 .distinct()
 .filter(v -> v%2==0)
 .map(v -> Math.sqrt(v))
 .collect(Collectors.toList());
 System.out.println("distinct");
 System.out.println(list2);
 }

 @Test
 public void sort() {
 List<Integer> list = generate(10);
 System.out.println("before");
 System.out.println(list);
 List<Integer> list2 = list.stream()
// .sorted(new Comparator<Integer>() {
// @Override
// public int compare(Integer o1, Integer o2) {
// return o2.intValue() - o1.intValue();
// }
// })
 .sorted((o1, o2) -> o2 - o1)
 .collect(Collectors.toList());
 System.out.println("sort");
 System.out.println(list2);
 int a;
 Integer b;
 }

 @Test
 public void groupby1() {
 // 按照奇偶数分组
 List<Integer> list = generate(10);
 System.out.println("before");
 System.out.println(list);
 Map<Boolean, List<Integer>> m1 = list.stream()
 .collect(Collectors.groupingBy(v->v%2==0));
 System.out.println(m1);

 Map<Boolean, Long> m2 = list.stream()
 .collect(Collectors.groupingBy(v->v%2==0, Collectors.counting()));
 System.out.println(m2);

 Map<String, Long> m3 = list.stream()
 .collect(Collectors.groupingBy(v->v%2==0?"偶数":"奇数", Collectors.counting()));
 System.out.println(m3);
 }
}