private static List<User> list = new ArrayList<User>();
public static void main(String[] args) {
list = Arrays.asList(
new User(1, "a", 10),
new User(4, "d", 19),
new User(5, "e", 13),
new User(2, "b", 14),
new User(3, "a", 10),
new User(6, "f", 16)
);
long start = System.currentTimeMillis();
order();
println(String.format("耗时[%s]毫秒", (System.currentTimeMillis() - start)));
}
/**
* 多条件去重
* @param list
*/
public static void order() {
list.stream().collect(Collectors.collectingAndThen(
Collectors.toCollection(() -> new TreeSet<>(
Comparator.comparing(o -> o.getAge() + ";" + o.getName()))), ArrayList::new)).forEach(u -> println(u));
}
public static void group() {
Map<Integer, List<User>> collect = list.stream().collect(Collectors.groupingBy(User::getAge));
System.out.println(collect);
}
/**
* filter过滤
* @param list
*/
public static void filterAge() {
list.stream().filter(u -> u.getAge() == 10).forEach(u -> println(u));
}
/**
* sorted排序
*/
public static void stord() {
list.stream().sorted(Comparator.comparing(u-> u.getAge())).forEach(u -> println(u));
}
/**
* limit方法限制最多返回多少元素
*/
public static void limit() {
list.stream().limit(2).forEach(u -> println(u));
}
/**
* 不要前多n个元素，n大于满足条件的元素个数就返回空的流
*/
public static void skip() {
list.stream().skip(2).forEach(u -> println(u));
}
// 最大值 最小值
public static void statistics() {
Optional<User> min = list.stream().min(Comparator.comparing(User::getUserId));
println(min);
Optional<User> max = list.stream().max(Comparator.comparing(User::getUserId));
println(max);
}
// 统计
public static void summarizingInt(){
IntSummaryStatistics statistics = list.stream().collect(Collectors.summarizingInt(User::getAge));
double average = statistics.getAverage();
long count = statistics.getCount();
int max = statistics.getMax();
int min = statistics.getMin();
long sum = statistics.getSum();
println(average);
println(count);
println(min);
println(sum);
println(max);
}
/**
* 转set
*/
public static void toSet() {
Set<User> collect = list.stream().collect(Collectors.toSet());
Iterator<User> iterator = collect.iterator();
while(iterator.hasNext()) {
System.out.println(iterator.next().getUserId());
}
}
/**
* 转map
*/
public static void toMap() {
Map<Integer, User> collect = list.stream().collect(Collectors.toMap(User::getUserId, u -> u));
for (Integer in : collect.keySet()) {
User u = collect.get(in);//得到每个key多对用value的值
println(u);
}
}
/**
*map
*/
public static void map() {
list.stream().map(User::getUserId).forEach(userId -> println(userId));
list.stream().mapToInt(User::getAge).forEach(userId -> println(userId));
list.stream().mapToDouble(User::getUserId).forEach(userId -> println(userId));
list.stream().mapToLong(User::getUserId).forEach(userId -> println(userId));
}
/**
* 查找与匹配
* allMatch方法与anyMatch差不多，表示所有的元素都满足才返回true。noneMatch方法表示没有元素满足
*/
public static void anyMatch() {
boolean anyMatch = list.stream().anyMatch(u -> u.getAge() == 100);
boolean allMatch = list.stream().allMatch(u -> u.getUserId() == 10);
boolean noneMatch = list.stream().noneMatch(u -> u.getUserId() == 10);
println(anyMatch);
println(allMatch);
println(noneMatch);
}
/**
* reduce操作
*/
public static void reduce() {
Optional<Integer> sum = list.stream().map(User::getAge).reduce(Integer::sum);
Optional<Integer> max = list.stream().map(User::getAge).reduce(Integer::max);
Optional<Integer> min = list.stream().map(User::getAge).reduce(Integer::min);
println(sum);
println(max);
println(min);
}
/**
* 公共输出
* @param c
*/
public static void println(Object c) {
System.out.println(c.toString());
}