///Java对象类
package cn.missbe.random.demo.study;
import com.xiaoleilu.hutool.util.RandomUtil;
public class Dish {
public enum Level{DIET,NORMAL,FAT}
public enum Type{MEAT,FISH,OTHER}
private final String name = RandomUtil.randomString(7);
private final int calories;
private final boolean vegetarian;
private final Type type;
public Dish(int calories, boolean vegetarian, Type type) {
this.calories = calories;
this.vegetarian = vegetarian;
this.type = type;
}
public boolean isVegetarian() {
return vegetarian;
}
public Type getType() {
return type;
}
public int getCalories() {
return calories;
}
public String getName() {
return name;
}
@Override
public String toString() {
return "Dish{" +
"name='" + name + '\'' +
", calories=" + calories +
", vegetarian=" + vegetarian +
", type=" + type +
'}';
}
}
//JUnit测试
package cn.missbe.random.demo.study;
import com.sun.org.apache.xpath.internal.operations.Bool;
import org.junit.Before;
import org.junit.Test;
import java.util.*;
import java.util.function.Predicate;
import java.util.stream.Collectors;
import java.util.stream.IntStream;
import java.util.stream.Stream;
public class DishTest {
List<Dish> menu;
@Before
public void before(){
menu = new ArrayList<>();
menu.add(new Dish(24,true, Dish.Type.FISH ));
menu.add(new Dish(34, true, Dish.Type.MEAT ));
menu.add(new Dish(34, false, Dish.Type.OTHER ));
menu.add(new Dish(22, true, Dish.Type.MEAT ));
menu.add(new Dish(65, false, Dish.Type.FISH ));
menu.add(new Dish(565,true, Dish.Type.OTHER ));
menu.add(new Dish(565, false, Dish.Type.FISH ));
menu.add(new Dish(55, true, Dish.Type.FISH ));
menu.add(new Dish(595, false, Dish.Type.MEAT ));
}
@Test
public void oldMethod(){
List<Dish> lowCaloricDisher = new ArrayList<>();
for(Dish d : menu){
if(d.getCalories() < 400){
lowCaloricDisher.add(d);
}
}
System.out.println(lowCaloricDisher);
}
@Test
public void optional(){
Comparator<Dish> dishCaloriesComparator = Comparator.comparing(Dish::getCalories);
Optional<Dish> mostCalorieDish = menu.stream().max(dishCaloriesComparator);
mostCalorieDish.ifPresent(System.out::println);
}
@Test
public void streamTest(){
Predicate<Dish> predicate = d->d.getCalories() < 400;
List<Integer> lowCaloricDisher = menu.stream().filter(predicate.negate())
.sorted(Comparator.comparing(Dish::getCalories))
.map(Dish::getCalories)
.collect(Collectors.toList());
System.out.println(lowCaloricDisher);
String names = menu.parallelStream().filter(predicate)
.map(Dish::getName)
.collect(Collectors.joining(","));
System.out.println("name:" + names);
}
@Test
public void parallelStreamTest(){
Predicate<Dish> predicate = d->d.getCalories() < 400;
List<Integer> lowCaloricDisher = menu.parallelStream().filter(predicate.negate())
.sorted(Comparator.comparing(Dish::getCalories))
.map(Dish::getCalories)
.distinct()
.skip(1)
.limit(2)
.collect(Collectors.toList());
System.out.println(lowCaloricDisher);
long count = menu.parallelStream().filter(d->d.getCalories() < 400)
.distinct()
.limit(3)
.count();
System.out.println(count);
}
@Test
public void consumer(){
List<String> title = Arrays.asList("java8", "in", "action");
Stream<String> s = title.stream();
s.forEach(System.out::println);
//流只能消费一次
//stream has already been operated upon or closed
s.forEach(System.out::println);
}
@Test
public void map_reduce(){
List<Dish> vegetarianMenu = menu.stream().filter(Dish::isVegetarian)
.collect(Collectors.toList());
System.out.println(vegetarianMenu);
int totalCalories = menu.stream().map(Dish::getCalories).reduce(0, (i, j) -> j + j);
System.out.println(totalCalories);
}
private Dish.Level getLevel(Dish dish) {
if(dish.getCalories() <= 400)
return Dish.Level.DIET;
else if(dish.getCalories() <= 500){
return Dish.Level.NORMAL;
}else{
return Dish.Level.FAT;
}
}
@Test
public void group(){
//一级分类
Map<Dish.Type, List<Dish>> dishesByType = menu.stream().collect(Collectors.groupingBy(Dish::getType));
System.out.println(dishesByType);
Map<Dish.Level,List<Dish>> dishesByLevel = menu.stream().collect(Collectors.groupingBy(this::getLevel));
System.out.println(dishesByLevel);
///二级分类
Map<Dish.Type,Map<Dish.Level,List<Dish>>> dishesByTypeLevel = menu.stream().collect(Collectors.groupingBy(Dish::getType,Collectors.groupingBy(this::getLevel)));
System.out.println(dishesByTypeLevel);
///按子组收集类别多少
Map<Dish.Type, Long> typesLong = menu.stream().collect(Collectors.groupingBy(Dish::getType, Collectors.counting()));
System.out.println(typesLong);
}
@Test
public void partitioned(){
Map<Boolean, List<Dish>> partitionedMenu = menu.stream().collect(Collectors.partitioningBy(Dish::isVegetarian));
System.out.println(partitionedMenu);
Map<Boolean, Long> partitionedCount = menu.stream().collect(Collectors.partitioningBy(Dish::isVegetarian, Collectors.counting()));
System.out.println(partitionedCount);
}
@Test
public void primeTest(){
Map<Boolean, List<Integer>> primeMap = partitionPrimes(100);
System.out.println(primeMap);
}
private boolean isPrime(int candidate){
return IntStream.range(2,candidate).noneMatch(i->candidate % i==0);
}
public Map<Boolean,List<Integer>> partitionPrimes(int n){
return IntStream.rangeClosed(2, n).boxed()
.collect(Collectors.partitioningBy(this::isPrime));
}
@Test
public void peek(){
List<Integer> numbers = Arrays.asList(2, 3, 4, 5);
List<Integer> result =
numbers.stream()
.peek(x -> System.out.println("from stream: " + x))
.map(x -> x + 17)
.peek(x -> System.out.println("after map: " + x))
.filter(x -> x % 2 == 0)
.peek(x -> System.out.println("after filter: " + x))
.limit(3)
.peek(x -> System.out.println("after limit: " + x))
.collect(Collectors.toList());
System.out.println(result);
}
}
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