java-8

问题 I'm trying to use Java 1.8 with lambda expressions with Idea UI Designer , I have in maven: <plugin> <groupId>org.codehaus.mojo</groupId> <artifactId>ideauidesigner-maven-plugin</artifactId> <executions> <execution> <goals> <goal>javac2</goal> </goals> </execution> </executions> <configuration> <fork>true</fork> <debug>true</debug> <failOnError>true</failOnError> </configuration> </plugin> and dependency <dependency> <groupId>com.intellij</groupId> <artifactId>forms_rt</artifactId> <version>7

问题 When I see code snippets like interface A { void a(); void b() default { System.out.println("b"); }; void c() final { System.out.println("c"); }; } I have one question. Haven't we already got enough sh*t in Java? Why one might need this? 回答1: I suggest you to look at this conference : http://medianetwork.oracle.com/media/show/16999 This explain everything. The most interesting thing to do is to allow an interface to evolve without rewritting your whole codebase. This is key to allow a big

问题 Basically I look for a way to avoid working with entry -> entry.getValue and entry -> entry.getKey similar to what Map.forEach() does. If only I could get a way to work as map.stream().filter((k,v) -> ) ... and so on It seems the interface is called BiConsumer. Perhaps with a converter to BiConsumer or a Stream.generate() someway 回答1: Since this is a repeating question, I will throw a full solution into the ring. It’s a PairStream type that is by default a simple wrapper around an ordinary

问题 I am going through the lambda expression in java 8 when i changed the code of thread it's working fine new Thread(new Runnable() { @Override public void run() { System.out.println("run"); } }).start(); is converted to lambda expression as new Thread( () -> System.out.println("Hello from thread") ).start(); But i am not able to convert the FilenameFilter Expression File file = new File("/home/text/xyz.txt"); file.list(new FilenameFilter() { @Override public boolean accept(File dir, String name

问题 For the Collectors.groupingBy() that returns Map<K,List<T>> is it implied that the List<T> is in order that the stream is evaluated? I see no explicit description of the ordering of the list, whereas the concurrent version explicitly states no ordering. If it weren't ordered somehow, I'd expect it to be a Collection though, and I don't see what other ordering it could possibly be, other than order received. I'm hoping it's guaranteed that the last value in each list is the last value received

问题 I have a List of Integer say list1, and I want to get another list list2 which will contain the cumulative sum up until the current index from start. How can I do this using Stream API java 8 ? List<Integer> list1 = new ArrayList<>(); list1.addAll(Arrays.asList(1, 2, 3, 4)); List<Integer> list2 = new ArrayList<>(); // initialization list2.add(list1.get(0)); for(int i=1;i<list1.size();i++) { // increment step list2.add(list2.get(i-1) + list1.get(i)); } How can I change above imperative style

问题 I would like to merge two Map with JAVA 8 Stream: Map<String, List<String>> mapGlobal = new HashMap<String, List<String>>(); Map<String, List<String>> mapAdded = new HashMap<String, List<String>>(); I try to use this implementation: mapGlobal = Stream.of(mapGlobal, mapAdded) .flatMap(m -> m.entrySet().stream()) .collect(Collectors.groupingBy(Map.Entry::getKey, Collectors.mapping(Map.Entry::getValue, Collectors.toList()) )); However, this implementation only create a result like: Map<String,

问题 Below is the code that defines enum type. enum Company{ EBAY(30), PAYPAL(10), GOOGLE(15), YAHOO(20), ATT(25); private int value; private Company(int value){ super(this.name()); this.value = value; } public int getValue(){ return value; } } that gets internally compiled to, final class Company extends Enum<Company>{ public final static Company EBAY = new Company(30); public final static Company PAYPAL = new Company(10); public final static Company GOOGLE = new Company(15); public final static

问题 Reading about what kind of bytecode Java 8 produces from lambdas, it came to my mind the time when Java 5 was released. Back then there was Retroweaver and other tools for converting bytecode compiled with JDK 5 to run on JRE 1.4. Has anybody yet created such a backporting tool for Java 8 lambdas? It would let Java developers start using lambdas already today on production-quality Java 7 JREs, without having to wait 6-12 months for Java 8's GA release. Here is my analysis of why such as

问题 Reading about what kind of bytecode Java 8 produces from lambdas, it came to my mind the time when Java 5 was released. Back then there was Retroweaver and other tools for converting bytecode compiled with JDK 5 to run on JRE 1.4. Has anybody yet created such a backporting tool for Java 8 lambdas? It would let Java developers start using lambdas already today on production-quality Java 7 JREs, without having to wait 6-12 months for Java 8's GA release. Here is my analysis of why such as