java - Merge Sort on Object Linked List (ascending order) -

i working on homework assignment , after days of effort cannot figure out why, after mergesort implemented, list contains last object in linked list. not output entire linked list, last object. how can change code stop list turning null after 1 object.

please note: though call them cubes, know not since have random lengths, widths, , heights. assignment specifies called cubes, these random data fields. please ignore this.

public class sortingcubes {     public static void main(string[] args) {         system.out.println(" ");         system.out.println("-----my linked list-----");         cube headcubell = new cube();                           //create head cube         int llnum = 5;                                          //change number of linked list items desired here         for(int = 0; < llnum; i++) {             headcubell.length = math.random() * 99 + 1;         //create random l,w,h each cube (between 1-100)             headcubell.width = math.random() * 99 + 1;             headcubell.height = math.random() * 99 + 1;             headcubell.next = null;                             //sets end of list null             if(headcubell.next == null) {                       //creates new cube until desired number reached in loop                 cube curr = new cube(headcubell.length, headcubell.width, headcubell.height);                 headcubell = curr;             }             headcubell.next = null;                             //sets last cube (next) null end list.             system.out.println(headcubell.tostring() + " ");    //print linked list until end         }         system.out.println(" ");         system.out.println("-----new linked list after merge sort method implemented (asending order volume)-----");         long starttimemergesort = system.nanotime();         mergesort(headcubell);         long timeelapsedmergesort = (system.nanotime()- starttimemergesort);         printlist(headcubell);  //method print linked list                 system.out.println("objects in list " + count(headcubell));         long starttimeinsertionsort = system.nanotime();          system.out.println(" ");         system.out.println("time record: ");         system.out.println("time elapsed merge sort on linked list: " + timeelapsedmergesort + " nanos");       }       //end of main      public static void printlist(cube headcubell){         while(headcubell != null){             system.out.println(headcubell.tostring() + " ");             headcubell = headcubell.next;         }         system.out.println();     }      public static int count(cube head){         int count = 0;         while(head != null){             //system.out.println(head);             count++;             head = head.next;         }         return count;     }      public static cube mergesort(cube headcubell) {          if(headcubell == null || headcubell.next == null) {     //checking list null             return headcubell;         }         int count = 0;                  //to count total number of elements         cube temp = headcubell;         //temporary head of list          while(temp != null) {           //break list 2 parts             count++;                    //while not empty, count 1 , move temp temp.next evaluate             temp = temp.next;         }         int middle = count/2;           //create integer called middle , divide length of list (count) 2         cube = headcubell;            //another temp head cube 1st split list         cube b = null;                  //another cube null         cube temp2 = headcubell;        //create temp head cube 2nd list              int counthalf = 0;              //start @ half 0 again          while(temp2 != null) {          //while temp have 2nd list not null....              counthalf++;                    //add count length of linked list             cube thenext = temp2.next;      //create new cube assigned cube after head             if(counthalf == middle) {       //once reaches middle number                 temp2.next = null;          //end list (set head.next null list 2)                  b = thenext;                //take empty null cube , assign end null.              }             temp2 = thenext;                //otherwise - move along , temp head temp head.next         }         //now have 2 parts, list , list b.          cube half1 = mergesort(a);          //recursively call sort each half         cube half2 = mergesort(b);          //merge         cube merged = merge(half1, half2);  //call 2nd method merge 2 halves         //system.out.println(merged.tostring());     //print l,w,h , volume of each cube in array          return merged;      //return merged list.      }      public static cube merge(cube a, cube b) {      //parameters 2 half's of original list         cube pt1 = a;                   //2 parts going merge ascending lists according volume         cube pt2 = b;          cube temphead = new cube();         //temp head of new list cubes merged         cube ptnew = temphead;              //temp head list new list          while(pt1 != null || pt2 != null) {     //while either list not empty             if(pt1 == null) {                   //but if first null                   ptnew.next = new cube(pt2.cubevolume());    //create new cube every cube volume                 pt2 = pt2.next;                 //loop             }             else if(pt2 ==null){                //but if 2nd null                 ptnew.next = new cube(pt1.cubevolume());    //create new cube every cube volume                 pt1 = pt1.next;                 //loop                 ptnew = ptnew.next;             //move on assigning moving next cube creating when pt2 == null             }             else {                 if(pt1.cubevolume() < pt2.cubevolume()) {       //moving while merging - comparing volumes of head of each list                     ptnew.next = new cube(pt1.cubevolume());    //when 1 greater new cube creating in new list , cube placed accordingly                     pt1 = pt1.next;         //loop                     ptnew = ptnew.next;     //loop through new merged list next comparison                 }                 else if(pt1.cubevolume() == pt2.cubevolume()) { //statement if cubes volumes equal                     ptnew.next = new cube(pt1.cubevolume());                     ptnew.next.next = new cube(pt1.cubevolume());                     ptnew = ptnew.next.next;                     pt1 = pt1.next;             //place 1 next other                     pt2 = pt2.next;                 }                 else {                     ptnew.next = new cube(pt2.cubevolume());        //else made new cube in new list , place pt2 head                     pt2 = pt2.next;             //loop                       ptnew = ptnew.next;             //loop                 }              }         }         return temphead.next;           //return new merged list     }  }   //end of class 

my cube class: (all correct reference)

public class cube {      double length;     double width;     double height;     cube next = null;      public cube() { //default constructor     }     public cube(double volume) {         volume = this.cubevolume();     }      public cube(double length, double width, double height) {         this.length = length;         this.width = width;         this.height = height;         this.next = next;     }      public string tostring() {      //print string         return "cube volume: (" + cubevolume() + ") ----- cube length: ("+ this.length +") ----- cube width (" + this.width + ") ----- cube height (" + this.height + ")";     }     //set length     public void setlength(double length) {         this.length = length;     }      //get length     public double getlength() {         return this.length;     }      //set width     public void setwidth(double width) {         this.width = width;      }      //get width     public double getwidth() {         return this.width;     }      //set height     public void setheight(double height) {         this.height = height;     }      //set height     public double setheight() {         return this.height;     }      //set next     public void setnext(cube next) {         this.next = next;     }      //get next     public cube getnext() {         return this.next;     }      public double cubevolume () {         double volume = (length*width*height);         //system.out.println("test: " + volume);         return volume;     }  }       //end of class 

output

-----my linked list----- cube volume: (14550.645379921463) ----- cube length: (19.526751823368887) ----- cube width (54.77537177724803) ----- cube height (13.604009167732666)  cube volume: (1631.5144309742377) ----- cube length: (40.72878317573845) ----- cube width (22.07526604887876) ----- cube height (1.8146109949933575)  cube volume: (17837.576670179817) ----- cube length: (4.606784797762423) ----- cube width (78.5447210731351) ----- cube height (49.29704940251802)  cube volume: (113668.01972101796) ----- cube length: (24.366242383656253) ----- cube width (54.33809524521938) ----- cube height (85.85099307890556)  cube volume: (432771.5800393206) ----- cube length: (83.95704403819472) ----- cube width (56.0616051224998) ----- cube height (91.94668276748753)   -----new linked list after merge sort method implemented (asending order volume)----- cube volume: (432771.5800393206) ----- cube length: (83.95704403819472) ----- cube width (56.0616051224998) ----- cube height (91.94668276748753)   objects in list 1  time record:  time elapsed merge sort on linked list: 11831 nanos 

the problem in main method, not sorting methods. block

        headcubell.next = null;                             //sets end of list null         if(headcubell.next == null) {                       //creates new cube until desired number reached in loop             cube curr = new cube(headcubell.length, headcubell.width, headcubell.height);             headcubell = curr;         }         headcubell.next = null;    

will go if section. you're not setting next field of curr @ all. when assign curr headcubell, lose previous value of headcubell. means there ever 1 object in list. throwing away object each time create new one.

you need

• remove final headcubell.next = null;
• add new line curr.setnext(headcubell); after object curr created.

that way, previous headcubell remembered, next element of new object created.