JAVA: How to join a HashTable with itself? -

what elegant way join 2 hashtables?

i have hashtable , cannot use array or list or set instead, because messes dealing custom-class. @ least that's think.

        **hashtable<itemset, integer> frequentitemsetl1 = new hashtable<>();**         (map.entry<itemset, integer> entry : candidateitemsetc1.entryset()) {         if (entry.getvalue() >= supportthreshold) {             frequentitemsetl1.put(entry.getkey(), entry.getvalue());         } 

which contains: key-value-pairs.

• key = number of itemset
• value = number of occurrences of itemset in data

looks this:

{1}, 3 {2}, 23 {3}, 7 {4}, 18 .....  

i need keys of frequentitemsetl1 join themselves;

result should be:

{1, 2} {1, 3} {1, 4} {2, 3} {2, 4} {3, 4} 

i experimented 2 for-loops , keysets did not far. need fresh ideas.

tried this:

for (int = 0; < frequentitemsetl1.size(); i++) {         integer item1 = frequentitemsetl1.get(i);         (int j = + 1; j < frequentitemsetl1.size(); j++) {             integer item2 = frequentitemsetl1.get(j);              // create new candidate combining itemset1 , itemset2             candidateitemsetc2.put(item1, item2);         } 

since nobody able help, clarify , others, looking this:

list<itemset> candidateitemsetc2 = new arraylist<>();     hashtable<itemset, integer> frequentitemsetl2 = new hashtable<>();     // each itemset i1 , i2 of level k-1     (itemset : frequentitemsetl1.keyset()) {         (itemset is2 : frequentitemsetl1.keyset()) {             if (is.equals(is2)) {                 continue;             }             if (is.set.length != is2.set.length) {                 continue;             }             boolean shouldjoin = true;             (int = 0; < is.set.length - 1; i++) {                 if (is.set[i] != is2.set[i]) {                     shouldjoin = false;                 }             }              if (shouldjoin == false) {                 continue;             }              int[] join = new int[is.set.length + 1];             (int = 0; < is.set.length; i++) {                 join[i] = is.set[i];             }             join[join.length - 1] = is2.set[is2.set.length - 1];             arrays.sort(join);             itemset joinedset = new itemset(join);              if (!candidateitemsetc2.contains(joinedset)) {                 candidateitemsetc2.add(joinedset);             }               (int p = 0; p < candidateitemsetc2.size(); p++) {                 //system.out.print(candidateitemsetc2.get(p));             }           }