jdk1.8 List 去重

元素去重

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;
public class DistinctSimpleDemo {
    public static void main(String[] args) {
        List<String> list = Arrays.asList("AA", "BB", "CC", "BB", "CC", "AA", "AA");
        long l = list.stream().distinct().count();
        System.out.println("No. of distinct elements:"+l);
        String output = list.stream().distinct().collect(Collectors.joining(","));
        System.out.println(output);
    }
}

输出

No. of distinct elements:3
AA,BB,CC

通过对象中的某个属性进行去重

import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.function.Function;
import java.util.function.Predicate;
public class DistinctByProperty {
    public static void main(String[] args) {
        List<Book> list = new ArrayList<>();
        {
        	list.add(new Book("Core Java", 200));
        	list.add(new Book("Core Java", 300));
        	list.add(new Book("Learning Freemarker", 150));
        	list.add(new Book("Spring MVC", 200));
        	list.add(new Book("Hibernate", 300));
        }
        list.stream().filter(distinctByKey(b -> b.getName()))
              .forEach(b -> System.out.println(b.getName()+ "," + b.getPrice()));   
    }
    private static <T> Predicate<T> distinctByKey(Function<? super T, ?> keyExtractor) {
        Map<Object,Boolean> seen = new ConcurrentHashMap<>();
        return t -> seen.putIfAbsent(keyExtractor.apply(t), Boolean.TRUE) == null;
    }
}

输出

Core Java,200
Learning Freemarker,150
Spring MVC,200
Hibernate,300

参考：https://blog.csdn.net/haiyoung/article/details/80934467