collections

问题 In a test class using AssertJ, I have code similar to the following: public void someTest() { assertThat(getNames()).has(sameNamesAs(getExpectedNames())); assertThat(getNames()).doesNotHave(sameNamesAs(getOtherNames())); } private List<String> getNames() { return null; } private List<String> getExpectedNames() { return null; } private List<String> getOtherNames() { return null; } private Condition<List<String>> sameNamesAs(List<String> rhs) { return new Condition<List<String>>("same names as

问题 I have a Set of expensive objects. These objects have IDs and the equals uses these IDs for equality. These objects' type has two constructors; one for the expensive object, and one that just sets the ID. So I can check if a particular ID is in the Set using Set.contains(new Object(ID)) . However, having determined the object is in the set, I cannot get the object instance in the set. How can I get the exact object that the set contains? 回答1: Consider using the UnifiedSet class in Eclipse

问题 I can do this quite easily, and cleanly, using a for loop. For instance, if I wanted to traverse a Seq from every element back to itself I would do the following: val seq = Seq(1,2,3,4,5) for (i <- seq.indices) { for (j <- seq.indices) { print(seq(i + j % seq.length)) } } But as I'm looking to fold over the collection, I'm wondering if there is a more idiomatic approach. A recursive approach would allow me to avoid any var s. But basically, I'm wondering if something like the following is

问题 When is it acceptable for an indexer to automatically add items to a collection/dictionary? Is this reasonable, or contrary to best practices? public class I { /* snip */ } public class D : Dictionary<string, I> { public I this[string name] { get { I item; if (!this.TryGetValue(name, out item)) { item = new I(); this.Add(name, item); } return item; } } } Sample of how this may be used in a collection: public class I { public I(string name) {/* snip */} public string Name { get; private set; }

问题 This question already has answers here : Incompatible types List of List and ArrayList of ArrayList (6 answers) Initialize List<List<Integer>> in Java (2 answers) Closed 2 years ago . I want to understand the difference between the two definitions and why the correct one is correct and the wrong is wrong. The one showing me the compile-error List<List<Integer>> arr2 = new ArrayList<ArrayList<Integer>>(); The error it gave me : try2.java:8: error: incompatible types: ArrayList<ArrayList

问题 I have below this two classes .. class Emp //implements Comparable { String name,job; public String getName() { return name; } public void setName(String name) { this.name = name; } public String getJob() { return job; } public void setJob(String job) { this.job = job; } public int getSalary() { return salary; } public void setSalary(int salary) { this.salary = salary; } int salary; public Emp(String n,String j,int sal) { name=n; job=j; salary=sal; } public void display() { System.out.println

问题 This takes around 1 second (1 to 1000000).map(_+3) While this gives java.lang.OutOfMemoryError: Java heap space (1 to 1000000).par.map(_+3) EDIT: I have standard scala 2.9.2 configuration. I am typing this on scala prompt. And in the bash i can see [ -n "$JAVA_OPTS" ] || JAVA_OPTS="-Xmx256M -Xms32M" AND i dont have JAVA_OPTS set in my env. 1 million integers = 8MB, creating list twice = 16MB 回答1: It seems definitely related to the JVM memory option and to the memory required to stock a

问题 Is there a fast way to copy a generic TList? Copy.Capacity := List.Count; for Item in List do Copy.Add (Item); is very slow. There seems to be no way to use CopyMemory since I can't get the memory adress of the internal array (which is obvious from an information hiding viewpoint). I miss something like List.Copy (Copy); which uses the knowledge of the internal representation to improve performance. Can it be done? 回答1: For the generic TList<T> it is simply not possible to implement the

问题 Is there a fast way to copy a generic TList? Copy.Capacity := List.Count; for Item in List do Copy.Add (Item); is very slow. There seems to be no way to use CopyMemory since I can't get the memory adress of the internal array (which is obvious from an information hiding viewpoint). I miss something like List.Copy (Copy); which uses the knowledge of the internal representation to improve performance. Can it be done? 回答1: For the generic TList<T> it is simply not possible to implement the

问题 I have some code with Map<String, Map<String, String>> objects, which works (it is instantiated as a HashMap of HashMaps), but I wonder whether there is a better way to represent this data structure in Guava. I have considered Multimap , but while there is ListMultimap and SetMultimap in Guava, I have found no "MapMultimap". I have also checked Table, which seems to be more like it, but its name is making me uncomfortable: what I have is definitely not a table but a tree. (There is no overlap