hashmap

问题 I've just started learning about hash tables and I understand how to insert but not how to search. These are the algorithms I'll be basing this question off: Hashing the key int Hash (int key) { return key % 10; //table has a max size of 10 } Linear probing for collision resolution. Suppose I call insert twice with the keys 1, 11, and 21. This would return slot 1 for all 3 keys. After collision resolution the table would have the values 1, 11, and 21 at slots 1, 2, and 3. This is what I

问题 In the implementation details of HashMap , I can read: When using comparators on insertion, to keep a * total ordering (or as close as is required here) across * rebalancings, we compare classes and identityHashCodes as * tie-breakers. If I have constant hashCode and fine equals and my class doesn't implement Comparable how exactly it will break the ties and how the tree will be constructed? I mean - bucket will transform to a tree and will use System.identityHashCode to break a tie. Then I

问题 public class Dashboard { int REQUEST_ID, PRICE, PROCESSED; String LOGIN_USER; public int getREQUEST_ID() { return REQUEST_ID; } public void setREQUEST_ID(int rEQUEST_ID) { REQUEST_ID = rEQUEST_ID; } //all getters and setters public class DBConnection { public ArrayList<Dashboard> getStoreResult() { ArrayList<Dashboard> dashRec; try{ Class.forName(""); Connection con=DriverManager.getConnection(""); Statement st=con.createStatement(); ResultSet rs=st.executeQuery(""); HashMap<Object, List

问题 public class Dashboard { int REQUEST_ID, PRICE, Status; String LOGIN_USER; public int getREQUEST_ID() { return REQUEST_ID; } public void setREQUEST_ID(int rEQUEST_ID) { REQUEST_ID = rEQUEST_ID; } //all getters and setters public class MapKey { private Integer id; private String name; public MapKey(Integer id, String name) { this.id = id; this.name = name; } @Override Hashcode and equals public class DBConnection { public ArrayList<Dashboard> getStoreResult() { ArrayList<Dashboard> dashRec;

问题 New to hashtables with a simple question. For some reason googling hasn't gotten me a straight answer. Say I've got an <int,String> hashtable set up: myHashtable.put(1,"bird"); myHashtable.put(2,"iguana"); and I want to change "bird" to "fish" (and leave the index the same). Can I just do a simple put , or do I need to delete the entry, or what? 回答1: Yes. If a mapping to the specified key already exists, the old value will be replaced (and returned). See Hashtable.put(). For multi-threaded

问题 New to hashtables with a simple question. For some reason googling hasn't gotten me a straight answer. Say I've got an <int,String> hashtable set up: myHashtable.put(1,"bird"); myHashtable.put(2,"iguana"); and I want to change "bird" to "fish" (and leave the index the same). Can I just do a simple put , or do I need to delete the entry, or what? 回答1: Yes. If a mapping to the specified key already exists, the old value will be replaced (and returned). See Hashtable.put(). For multi-threaded

问题 New to hashtables with a simple question. For some reason googling hasn't gotten me a straight answer. Say I've got an <int,String> hashtable set up: myHashtable.put(1,"bird"); myHashtable.put(2,"iguana"); and I want to change "bird" to "fish" (and leave the index the same). Can I just do a simple put , or do I need to delete the entry, or what? 回答1: Yes. If a mapping to the specified key already exists, the old value will be replaced (and returned). See Hashtable.put(). For multi-threaded

问题 I need to iterate through a BucketMap and get all keys but how do I get to something like buckets[i].next.next.next.key for instance without doing it manually as I tried here: public String[] getAllKeys() { int j = 0; //index of string array "allkeys" String allkeys[] = new String[8]; for(int i = 0; i < buckets.length; i++) { //iterates through the bucketmap if(buckets[i] != null) { //checks wether bucket has a key and value allkeys[j] = buckets[i].key; //adds key to allkeys j++; // counts up

问题 If I want to write an object / HashTable to disk and load it up again later does PowerShell support that? 回答1: Sure, you can use PowerShell's native CliXml format: @{ a = 1 b = [pscustomobject]@{ prop = "value" } } | Export-Clixml -Path hashtable.ps1xml Deserialize with Import-CliXml: PS C:\> $ht = Import-CliXml hashtable.ps1xml PS C:\> $ht['b'].prop -eq 'value' True 回答2: The answer may depend on the data in your hashtable. For relatively simple data Export-Clixml and Import-CliXml is the

问题 I have a CSV file that contains roughly 500,000 rows and 22 columns of flight data. The 5th Column contains the tail number of each plane for each flight. The 22nd column contains the distance traveled for each flight. I'm attempting to sum the total distance traveled (column 22) for each tail number (column 5). I created a HashMap containing all data named map1 . I created a 2nd HashMap named planeMileages to place each flight number and its total distance traveled into. I'm using a nested