[問題] 找得到內容卻print不出來

看板java作者miyabichan (miyabichan)時間11年前 (2013/11/28 00:05)推噓1(1推 0噓 14→)

留言15則, 7人參與討論串1/1

這個作業我們要自己實作只能存正整數 integer 的一個 chained hash table, 然後寫四個 Method 分別是 insert, delete, lookup 跟 print.. 我的問題在 print 這個部份。資料結構我選擇用 Hashmap, 用 Hash function 算出來的雜湊數存成 Key, Value 則用 LinkedList.. 測試的時候 insert 跟 lookup 都沒問題，但我要把他 print 出來的時候卻說所有 Hashmap 的 value (= LinkedList) 是 null.. 我想了很久找不出盲點在哪裡，可不可以請厲害的眾板友指點我一下？先謝過了！（以下程式碼我就略過 main Method..） public class HashTable { private int a, n, m; private Map<Long, LinkedList<Integer>> ht = new HashMap<Long, LinkedList<Integer>>(); /** * Constructor * @param a, n, m: the parameters for hash function: * h(x) = (a*x mod n) mod m. * and the hashtable should have size of m */ public HashTable(int a, int n, int m){ this.a = a; this.n = n; this.m = m; for(long i = 0; i < m; i++){ ht.put(i, new LinkedList<Integer>()); } } /** * @return ture if x positiv, otherwise false. */ public boolean positiv(int x){ return (x >= 0); } /** * @param value: the object to be inserted in the hashtable * insert the number in the hash table, * index calculate through the hash function given. */ public void insert(int value){ if(positiv(value)){ long key = (a * value % n) % m; ht.get(key).add(value); } } /** * @param value: the object to be found * @return true if the value in the hashtable */ public boolean lookup(int value){ if(!positiv(value)){ return false; } long key = ((a * value) % n) % m; return ht.get(key).contains(value); } /** * @param value: the object to be deleted * Removes the (first) occurrence of the specified element * from this hashtable, if it is present */ public void delete(int value){ if(positiv(value)){ long key = ((a * value) % n) % m; ht.get(key).remove((Object) value); // if not with Object typecasting, // program will "see" the value (int) as an index // (better solution ?) } } /** * print out the hashtable */ public void print(){ for(int key = 0; key < m; key++){ System.out.print(key + " "); // output index if(ht.get(key) != null){ for(int i = 0; i < ht.get(key).size(); i++){ System.out.print(ht.get(key).get(i) + " "); } } System.out.println(); } } -- ※ 發信站: 批踢踢實業坊(ptt.cc) ◆ From: 134.93.102.77

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PsMonkey

11/28 00:16, , 1^F

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miyabichan

11/28 00:18, , 2^F

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miyabichan

11/28 00:19, , 3^F

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