java-stream

问题 I wanted to do some performance measurements and comparisons of simple for loops and equivalent streams implementations. I believe it's the case that streams will be somewhat slower than equivalent non-streams code, but I wanted to be sure I'm measuring the right things. I'm including my entire jmh class here. import java.util.ArrayList; import java.util.List; import org.openjdk.jmh.annotations.Benchmark; import org.openjdk.jmh.annotations.Scope; import org.openjdk.jmh.annotations.Setup;

问题 I want to determine if a list is anagram or not using Java 8. Example input: "cat", "cta", "act", "atc", "tac", "tca" I have written the following function that does the job but I am wondering if there is a better and elegant way to do this. boolean isAnagram(String[] list) { long count = Stream.of(list) .map(String::toCharArray) .map(arr -> { Arrays.sort(arr); return arr; }) .map(String::valueOf) .distinct() .count(); return count == 1; } It seems I can't sort char array with Stream.sorted()

问题 This question already has answers here : Stream intermediate operations ordering (2 answers) Closed last year . I have been trying to find clear contract from official Java documentation as to in which order Java streams, once a terminal operation is called, process the elements and call intermediate operations. For example lets look at these examples that use both Java stream version and plain iteration version (both producing same outcome) . Example1: List<Integer> ints = Arrays.asList(1, 2

问题 I am building an object with a simple loop: WebTarget target = getClient().target(u); for (Entry<String, String> queryParam : queryParams.entrySet()) { target = target.queryParam(queryParam.getKey(), queryParam.getValue()); } I want to do the same thing using the Java8 Stream API but I cannot figure out how to do it. What makes me struggle is that target is reassigned every time, so a simple .forEach() will not work. I guess I need to use a .collect() or reduce() since I am looking for a

问题 List<Integer> integer = Stream.generate(new Supplier<Integer>() { int i = 0 ; @Override public Integer get() { return ++i; } }).filter(j -> j < 5) .limit(10) // Note the call to limit here .collect(Collectors.toList()); Counter to my expectation, the collect call never returns. Setting limit before filter produces the expected result. Why? 回答1: Since there are only 4 elements that pass the filter, limit(10) never reaches 10 elements, so the Stream pipeline keeps generating new elements and

问题 I am using java 8 stream API to perform action on a list of Store objects. Store takes a String argument and a Mapper object. Mapper will be same for all Store object. Question: How can I pass Mapper object when I initialize Store here .map(Store::new) ? public class Store { public Store(String name, Mapper mapper) { } } public class Mapper { } public class Test { public static void main(String[] args) { List<String> names = new ArrayList<String>(); Mapper mapper = new Mapper(); // compile

问题 I want to determine the minimum area required to display a collection of points. The easy way is to loop through the collection like this: int minX = Integer.MAX_VALUE; int maxX = Integer.MIN_VALUE; int minY = Integer.MAX_VALUE; int maxY = Integer.MIN_VALUE; for (Point point: points) { if (point.x < minX) { minX = point.x; } if (point.x > maxX) { maxX = point.x; } if (point.y < minY) { minY = point.y; } if (point.y > maxY) { maxY = point.y; } } I am getting to know streams. To do the same,

问题 I'm working on spring-boot application with JPA. In the code I found a really suspicious part which does something like (simplified example, the code otherwise contains a lot of clutter): entityRepository.findAll().parallel() // The findAll returns already a stream, it's a CrudRepository from Spring .filter (...) .map(e -> { OtherDbObject other = service.getOtherDbObjectBasedOn(e); boolean hasSomething = other.getProperties().stream() //properties is fetch type EAGER @OneToMany collection in

问题 I'm a novice Java programmer at university. I discovered something today that broke one of my conceptions about how Java syntax works. public class testClass { ArrayList <String> persons = new ArrayList <String> (); public void run(){ Stream <String> personstream = persons.stream(); }} The method stream() is not found in the ArrayList class, yet it might appear as if it's there. When I move my mouse over the stream() -method in Eclipse, it says it's part of Collections, but I don't find the

问题 Steps: Go to the site > https://www.toolsqa.com/automation-practice-switch-windows/ Get a list of buttons from that page Print the name of the buttons that are displayed on the page. Code trial: package com.practice; import java.util.List; import org.openqa.selenium.By; import org.openqa.selenium.WebDriver; import org.openqa.selenium.WebElement; import org.openqa.selenium.chrome.ChromeDriver; public class Buttons { public static void main(String[] args) throws InterruptedException { System